# Opinion about transmission service.



## HotRodx10 (Aug 24, 2017)

The vehicles I've heard of that developed problems after a flush were either fairly old or had gone for over 200,000 miles without a flush. 

It's anecdotal, of course, but I had about that many miles on my minivan's transmission when I did the first flush. I didn't cause any problems. It actually shifted a little smoother afterwards.

Would you DIY, or have it done?


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## oggy bleacher (May 3, 2011)

After rebuilding a ford transmission valve body and transmission i really doubt the science behind flushing the transmission without rebuilding the valve body. The tolerance in a valve body is extremely small. No way to force clean fluid through it along with crud..,and the crud in a valve body should be manually cleaned. Almost all shifting problems start in a dirty valve body. I would only flush the transmission if i were going to rebuild the valve body myself or have someone reliable do it. Then i would just change the tranny fluid and filter and pan gasket...add an inline filter....maybe a radiator...and clean the valve body. A transmission rebuild can be $4k but just cleaning the valve body is much less depending on the make and model.
But inspecting the fluid pan for shavings tells a lot.


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## mark sr (Jun 13, 2017)

I'd just drain the fluid, replace the filter along with inspecting the bottom of the pan. That doesn't replace all the fluid but IMO the old remaining fluid isn't a big deal.


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## Mike Milam (Mar 3, 2017)

mark sr said:


> I'd just drain the fluid, replace the filter along with inspecting the bottom of the pan. That doesn't replace all the fluid but IMO the old remaining fluid isn't a big deal.


Been my practice for 50 years and never had one fail as a result.


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## Steve2444 (Sep 28, 2020)

I would drop the pan clean/replace the filter, add fresh fluid.
One thing I have done after that on older cars was to use an oil sucker, topsider, after a few weeks of driving I would use the topsider to remove all the fluid from the oil pan and replace. Repeat after a few weeks of driving.

Gets out some more of the old fluid along with the added new. Makes the concentration of new higher.



Amazon.com


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## raylo32 (Nov 25, 2006)

This is pretty much what I do. Last time I did my truck trans I went a step further and disconnected the trans cooler return line, directed it to a container, and then ran the motor for a bit until I saw air. Then shut it down, topped it up, and repeated 3 times... then did a final fill. This isn't a real flush but gets almost all of the old fluid out. But you will also be OK doing it as below. I would avoid the professional flushes. Not sure they help, and they could actually cause issues.



mark sr said:


> I'd just drain the fluid, replace the filter along with inspecting the bottom of the pan. That doesn't replace all the fluid but IMO the old remaining fluid isn't a big deal.


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## Brainbucket (Mar 30, 2015)

If the fluid is black or dark brown, it's over. You can chance it but be ready to rebuild it. It might drive a mile or 2 then it quits pulling. If the fluid is red, it should take it. I have a BG transmission flush machine and I always tell them this may kill or save your transmission. You never know. I flushed my truck after I built the engine with 100,000 miles but the fluid was red. Did fine.


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## HotRodx10 (Aug 24, 2017)

raylo32 said:


> I did my truck trans I went a step further and disconnected the trans cooler return line, directed it to a container, and then ran the motor for a bit until I saw air. Then shut it down, topped it up, and repeated 3 times... then did a final fill. This isn't a real flush but gets almost all of the old fluid out.


I read that letting it get air in the system is bad for it, so I did a similar thing on my Sienna, except I drained it (the pan has a drain plug, which not all vehicles do), refilled it (about 4 quarts), then took disconnected a cooler line, ran it until about 2 quarts came out (took about 1 minute, so I shifted through all the gears while doing so), put 2 quarts in, repeat until new fluid starts to come out looking new (3 times), reconnected the line, topped it off, and done. It took 12 quarts, which is supposedly the full fluid capacity, so I think I got it nearly all changed.

That was about 70,000 miles ago, and it's been working fine, other than it's starting to get a little sluggish shifting again. I guess it's time to do it again.


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## raylo32 (Nov 25, 2006)

Not really getting air in it. Just shutting it down with remote starter at the first little blip in the steady stream. I did this into a graduated clear container so could easily anticipate this on the second and third instances.



HotRodx10 said:


> I read that letting it get air in the system is bad for it, so I did a similar thing on my Sienna, except I drained it (the pan has a drain plug, which not all vehicles do), refilled it (about 4 quarts), then took disconnected a cooler line, ran it until about 2 quarts came out (took about 1 minute, so I shifted through all the gears while doing so), put 2 quarts in, repeat until new fluid starts to come out looking new (3 times), reconnected the line, topped it off, and done. It took 12 quarts, which is supposedly the full fluid capacity, so I think I got it nearly all changed.
> 
> That was about 70,000 miles ago, and it's been working fine, other than it's starting to get a little sluggish shifting again. I guess it's time to do it again.


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## SoNic (Feb 14, 2021)

Brainbucket said:


> If the fluid is black or dark brown, it's over.


Depends. Some fluids get dark very quick (like about 30-40k miles) because their dye oxidizes fast. Toyota and Hyundai/Kia OE fluids do that. I still hate when I see it, so I never use back the OE fluids.
On my Toyota I use Aisin synthetic WS fluid, on my other Kia and Hyundai I use Castrol.
Never happened to my former Ford vehicles.

I do periodically a drain/refill. That consists of three sets of 4 qt fluid drain/filled (my transmission pan and cooler capacity), separated by 200 mile drives. I think it achieves the same results as the cooler line job, and is way less risky.


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## pumpkin11 (Oct 31, 2020)

jbfan said:


> I'm buying a newer truck with 125K miles, and the transmission has never been flushed.


i don't believe in flushing,

i do regular drain and fills, i suggest you do the same


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## jbfan (Jul 1, 2004)

To answer some questions.
I would have my local shop do the work.
As far as I can tell, it is a closed system, as we could not find a dipstick when the shop inspected the truck for me.
In all my years of owning vehicles, I have flushed one transmission, and that was because it was slipping under load, and that fixed the problem.

Well, I found the dipstick!


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## Steve2444 (Sep 28, 2020)

Uggg, sealed system, just have the shop drop the pan, clean/replace the filter refill.


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## oggy bleacher (May 3, 2011)

F150? All my work trucks are f150 and i am not a fan in any condition. 8 hour job to replace a headlight?


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## SoNic (Feb 14, 2021)

jbfan said:


> As far as I can tell, it is a closed system


Depends of the year. Sometimes they just plugged the former dipstick hole with a rubber/plastic piece.


oggy bleacher said:


> 8 hour job to replace a headlight?


Just an urban legend from Ford haters?

On my Sable, Explorer they had the same system like on this older F150, super easy to replace them, in less than 1 minute:





For newer ones, it takes maybe 5 minutes:


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## papereater (Sep 16, 2016)

Then there is the paper towel test. Take a drop of fluid and drop it on a clean white paper towel. It is miogrates out to over the size of a quarter and is pinkish, it is still good, no need to flush/wherever. It is is brownish, and does NOT migrate out to the size of a quarter is is bad fluid. Here:









How to Check and Add Transmission Fluid (Automatic and Manual)


Regular transmission fluid checks should be part of your maintenance routine. Here's how to do just that whether you have an automatic or manual...




cartreatments.com


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## FM3 (Aug 12, 2019)

The old style of flushing is what isn't recommended. High pressure and/or use of strong cleaning chemicals. I'd certainly do some kind of fluid change at 125,000. Or at 250,000. Fresh fluid is better than 250,000 mile fluid.

125,000 isn't necessarily even that many miles since various manufacturers don't even recommend a trans fluid change until 100,000 or so. Of course, some manufacturers have recommended never changing the fluid and call it "lifetime trans fluid," which is of course ridiculous.

If the pan doesn't already have a drain plug, the first time you drop the pan to clean it (and presumably change the filter) is a good time to consider adding a plug or putting on an aftermarket pan that has one so you don't have to remove 20 little bolts for every drain and fill.

Various manufacturers recommend doing drain and fills instead of full changes. I'd recommend that on high-mileage, neglected trans, with the theory that 1/3rd or so new fluid won't loosen up debris in the trans too fast to get clogged. Do like one drain and fill, gets 1/3rd or so out, drive 500 or whatever miles, do another, repeat again 500 miles later if the fluid still looks terrible. And then do a drain and fill every x thousand miles. Some people do 3x in the same day every 30,000, but seems like one every 10,000 or so miles would be a little better. Kind of nitpicking at that point.

If the miles are high and the fluid has never been changed, too much new fluid can make the trans go crazy. Some (all?) vehicles can have the trans computer setting reset for fresh fluid. Otherwise, the trans shift points being changed by the computer over time to compensate for the old fluid then doesn't know what to do if lots of new fluid is suddenly put in there, and it can take 100 maybe more miles for it to not act like it doesn't know what gear to be in.


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## Old Thomas (Nov 28, 2019)

Let’s look at how an automatic transmission works. The pump picks up fluid through the filter. Some of the oil goes to the high pressure circuits to run the tranny and then it returns to the pan. Remaining oil goes to the low pressure cooling circuit and back to the pan. A flush interrupts a cooling line with the flush equipment. So flushing is like putting a water hose in one end of a swimming pool and a hose removing water at the other end of the pool. It is not a direct 1 to 1 exchange like flushers say. Flushing is favored by providers because they can have a low skilled worker connect the machine, walk away and do something else, then return and unhook it. There is almost no labor=profit. The pan and magnet stay dirty, all the garbage removed is run through the filter and nothing is inspected. I pull the pan, wash and inspect it, replace the filter and put it together. Unless it is really burned, changing all the oil is not necessary. If it is really burned, too late. Oil does not wear out. The additive package and friction modifiers get used up. Changing the oil on a good tranny rejuvenates it. GM issued a TSB a few years ago that said to never use any external filling or flushing machine on any trans ever made by GM. Then they followed it up with another TSB that said dealerships are independently owned and some offer services not approved by GM.


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## oggy bleacher (May 3, 2011)

SoNic said:


> Just an urban legend from Ford haters?


Try it on a 2020. The entire front quarter panel and grill are in the way. Absurd. I love my Ford that was built in August 1969 so im more of a dumbass design hater.


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## SoNic (Feb 14, 2021)

FM3 said:


> Of course, some manufacturers have recommended never changing the fluid and call it "lifetime trans fluid," which is of course ridiculous.


That is a miss-understanding, based on not actually reading the manual. In ALL of those cases you will see a mention about "heavy usage" or similar that will require change of fluid at about 70-100 k miles. That "heavy usage" means usually stop and go traffic or ambient temperatures over 90F. That's like 90% of US cars, especially the ones operated in urban environments, south of Washinton DC latitude.


Old Thomas said:


> It is not a direct 1 to 1 exchange like flushers say.


I have argued about that with people in various places (including BITOG). They think that oil is like a toothpaste, if you push fresh oil on one tube, it will completely push the old oil out, with no mixing inside.
Drain and refills, with drives in between, do the same mixing and refreshing as the "hose" method.


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## FM3 (Aug 12, 2019)

SoNic said:


> That is a miss-understanding, based on not actually reading the manual. In ALL of those cases you will see a mention about "heavy usage" or similar that will require change of fluid at about 70-100 k miles. That "heavy usage" means usually stop and go traffic or ambient temperatures over 90F. That's like 90% of US cars, especially the ones operated in urban environments, south of Washinton DC latitude.


Well, no.
Volvo has been one of the biggest offenders of this.

2000 to 2015 or so era Volvos have big blank spots in the auto trans boxes on the "when to replace fluid" chart that goes up to 150,000 miles.
It even has asterisks that say to only check the fluid if there's a leak.
And then the manual says "Volvo recommends changing automatic transmission fluid every 53,500 miles only on vehicles used for towing."

Recent Volvos say no need to change it under normal conditions. Here's "adverse" conditions:
_Below are some examples of adverse driving conditions._

_towing a caravan or trailer_
_in mountainous regions_
_at high speeds_
_in temperatures colder than -30 °C or hotter than +40 °C._
I doubt that's 90% of US cars.

Transmission manufacturer ZF attacked BMW's lifetime claims years ago to get them to change it:








ZF Transmissions to BMW Automatic owners, "There's no such thing as lifetime fluid." - Alt Car news


Although highly biased, ZF brings up some good points in this video, mainly that there's no such thing as lifetime fluids when it comes to automatics.




tiremeetsroad.com




_An official ZF video surfaced on Reddit earlier today calling out BMW for even putting “lifetime oil” on their automatic transmission-equipped BMWs._
_
Basically, they say you should not listen to BMW’s provided sticker saying their automatic transmission oil is lifetime, and instead, you should probably drain and refill ATF fluid every 100,000 KM’s or 62,000ish miles. 

In the video ZF explains that, if you’ve bought a newer BMW and take a peek underneath at your transmission filter, you’ll probably see a warning sticker from BMW warning you that ATF inside is lifetime. _


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## FM3 (Aug 12, 2019)

Here's a couple fun BMW stories:
_So I went to the stealer today and asked about the auto tranny fluid change (I have 50k miles). I quickly told them not to give me any BS about the lifetime fill, to which the guy in the parts dept replies: no, it is lifetime and I will show you how I know... He says the ATF price for my model is beyond outrageous: $70 CAD per litre (and it takes 9 litres). When I laughed, he proceeds to pull up the price on his computer and he goes, oops, they've raised it to $100 CAD per litre so sir, he says, the fluid alone will run you $900 and that is why I am telling you it is lifetime fluid.

Then I go to the service lady and ask her: I am here to ask for the TRUTH about the auto tranny fluid and no BS please. She looks up my vin and says there is no kits available for the fluid change for my car (incl the filter about which I asked specifically), she says it is lifetime and this is what it means, end of story.

So clearly, they will not change it for me or tell me anything other than lifetime fluid --> get the hell out of here. And if I insist, they will charge me $900 just for the fluid. _

This one is for a manual but it's still amusing:
_I know this is an old thread but my post is still relevant. My first BMW was a 2007 335i 6 speed manual. It also had lifetime fluid. I called ZF and talk to a tech support engineer to find out when I should change it. At first he hesitated to deviate from what BMW claims. Then he said, "is it out of warranty?" I said it was and then he said "change it."_


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## SoNic (Feb 14, 2021)

The manual transmissions are very different than the classic automatics. No need to change that fluid.
The dual-clutch automatic transmissions are the same as manual transmissions, but controlled by electric actuators. So yeah, I can see them being "lifetime". The clutches will wear out firstly.

The classic automatic uses the fluid as clutch, and that's why it gets hot during shifting.

PS: For fun, here's a 52 year old transmission service:


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## WhatsWrongWithMyVehicle (9 mo ago)

Our suggestion would be to change the fluid (via a drain plug or dropping the transmission fluid pan) and change the filter if you can. We don't recommend the old school style of flushing the system.


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## BruceLem (Jan 25, 2020)

oggy bleacher said:


> F150? All my work trucks are f150 and i am not a fan in any condition. 8 hour job to replace a headlight?


8 hours to change a headlight?!

Does that include a 7 hour nap?


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## evermod (May 2, 2018)

The secret to long service life of ANY mechanical device is regular maintenance. For the numerous reasons previously stated "flushing" a transmission is BS, is pretty likely to create problems and was probably invented by a service department that needed something "extra" to sell vs a regular tranny service. Should that last bit of old transmission fluid remaining after a drain and replace really bother you there's nothing stopping you from doing back to back services until you're satisfied that every drop of fluid is "new"; not to say that's going to gain you anything.

Don't get me started on "lifetime" transmissions; NHTSA (or somebody) should crucify every OEM that pulls this. Refer to my opening statement regarding regular maintenance, advances in mechanical and/or fluid technology don't change the laws of physics; things subject to wear are (guess what) STILL gonna wear out. The idea of "lifetime" transmissions owe their existence to two things: lowering the apparent cost of maintenance and planned (hastened) obsolescence.

-Dan O.


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## HotRodx10 (Aug 24, 2017)

evermod said:


> The secret to long service life of ANY mechanical device is regular maintenance. For the numerous reasons previously stated "flushing" a transmission is BS, is pretty likely to create problems and was probably invented by a service department that needed something "extra" to sell vs a regular tranny service. Should that last bit of old transmission fluid remaining after a drain and replace really bother you there's nothing stopping you from doing back to back services until you're satisfied that every drop of fluid is "new"; not to say that's going to gain you anything.


I'm sure I didn't get "every drop of fluid" changed, but the passive flushing I did on my Sienna about 60,000 mile ago got nearly all of it. Much more than just draining the pan and refilling it, which would only get about 1/3 of the fluid changed, and even "back to back services" would only get theoretically just over half of the fluid changed (1/3 on the first + 1/3 of the 2/3 old fluid remaining on the second). Subsequent drain and refill efforts would be even less effective. 

My procedure, which hasn't caused any problems was:

1) Remove drain plug and drain reservoir (about 4 quarts)
2) Replace drain plug; refill reservoir
3) Disconnect a tranny cooler line at rubber to steel transition (remove spring clamp and pull - 2 minutes)
4) Attach rubber tubing to steel line, and put lines into a gallon milk jug.
5) Start the van, and let it run until 2 quarts have been pumped out (about 1 minute), and then turn it off; empty the jug.
6) Add 2 quarts of new fluid.
7) Repeat steps 5 & 6 until new fluid starts coming out in the jug (4 times draining old fluid & 3 times refilling).
8) Reconnect tranny cooler line; add 1 quart of new fluid.
9) Start the van; check and top off fluid as required.

12 quarts (90%+) of fluid changed at a cost of about $60 and an hour of my time.


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## pwcopy (Aug 27, 2017)

What is the year, make and model of the truck? I've lived in Metro Detroit for 27 years and worked in automotive marketing for GM and Ford, where I made friends in their respective engineering departments. Those folks all told me, "Always read and follow the owners manual." Once I had a local shop recommend a trans flush and fill on a 2006 Ford Fusion with 60k on the clock because "the fluid looks and smells bad." I looked in the owner's manual and there was NO service interval for trans fluid. So I called a trans engineer I'd met at Ford, who said, "Yeah, the fluid in that trans goes in at the factory looking and smelling like something that came out a a dirty aquarium. No need to change it." I asked why there was no service interval and he said, "It's a lifetime fill." When I see a shop recommending 5000-mile oil changes on my 2016 Lincoln MKZ when it's owner's manual says every 10k or when the built-in Oil Life Monitor says "Time to change your oil," I steer clear. Sorry guys, but our DIY obsession does not mix well with just about any vehicle built in the last 30 years. By the 1990s, metallurgy, manufacturing tolerances and lubrication chemistry had advanced light years ahead of what your grandpa, dad, shade tree mechanic and local shop guy could ever imagine. And today, they've gone far beyond that. So look in the owner's manual for the correct service interval and follow it. You'll save time and money. And if you insist on following old-fashioned advice: If it ain't broke, don't fix it.


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## pwcopy (Aug 27, 2017)

Don't get me started on "lifetime" transmissions; NHTSA (or somebody) should crucify every OEM that pulls this. Refer to my opening statement regarding regular maintenance, advances in mechanical and/or fluid technology don't change the laws of physics; things subject to wear are (guess what) STILL gonna wear out. The idea of "lifetime" transmissions owe their existence to two things: lowering the apparent cost of maintenance and planned (hastened) obsolescence.

-Dan O.

Absolutely disagree. I've lived in Metro Detroit for 27 years and worked in automotive marketing for GM, Ford, Volkswagen and Audi, spending time in their engineering departments as well. "Planned Obsolescense" is an obsolete concept in the auto industry. Air Quality, Fuel Economy and global competition now drive both the development of vehicles and the transition to EVs. U.S. automakers can't keep making the same engines and drivelines for decades while putting new sheetmetal on top of them like they did from the end of WWII to almost 2000. GM, Ford and Chrysler had almost 100% of the U.S. market to themselves after the war. Their arrogance in believing they knew best what to build and how to build it brought them to their knees in the face of foreign insurgence by the 1980s. Today, GM, Ford and Stellantis split less than 50% among themselves. Global competition doesn't care what we believe. The winners follow facts and proven science. That's what the majority of automakers do today.


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## Old Thomas (Nov 28, 2019)

I understand the concept of a lifetime fluid. But the engineers must have had some time frame in mind, something they won’t tell us. At some point in the development cycle, someone decided that it’s wear characteristics will meet its expected life cycle. If they said the fluid is good for a lifetime, which they consider to be 250,000 miles, I would be able to judge whether to drive it longer based on luck, rebuild it, service it hoping for a longer life, or sell it. I oppose the open ended “lifetime” service life. It is a weasel clause that means it will last till it dies, whenever that happens be.


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## FM3 (Aug 12, 2019)

pwcopy said:


> I've lived in Metro Detroit for 27 years and worked in automotive marketing for GM and Ford, where I made friends in their respective engineering departments. Those folks all told me, "Always read and follow the owners manual." Once I had a local shop recommend a trans flush and fill on a 2006 Ford Fusion with 60k on the clock because "the fluid looks and smells bad." I looked in the owner's manual and there was NO service interval for trans fluid. So I called a trans engineer I'd met at Ford, who said, "Yeah, the fluid in that trans goes in at the factory looking and smelling like something that came out a a dirty aquarium. No need to change it." I asked why there was no service interval and he said, "It's a lifetime fill."


"Lifetime fill." What does "lifetime" mean to a Ford engineer? Engineers should know to use actual numbers. "Lifetime fill" is meaningless unless they actually mean lifetime. 

I already posted a link about BMW claiming "lifetime fill" and then the actual manufacturer of the transmission makes a video showing why they should stop saying that and instead change it at 60k. Should people have believed BMW and the sticker on their trans that says "lifetime fill"?

Here's the scheduled maintenance manual for a 2006 Ford Fusion, and other 2006 Ford vehicles. It say vehicles with 4F5ON and 4F27E transmissions should change the trans fluid at 30k, 60k, 90k, etc. Vehicles with that trans include: Freestar, Taurus, Windstar, Lincoln Continental, Sable, Ford Focus, etc.



https://www.fordservicecontent.com/Ford_Content/catalog/owner_guides/06frdmg3e.pdf



If the "lifetime" fluid is so great, why isn't it in the Ford Taurus and Ford Focus?

Fords with CVTs it says change the fluid at 60k and 120k.

And then, 150,000 miles on that chart, it says change the auto trans fluid on everything (except CVT). The only 2006 Fords I see with a CVT are Freestyle and Five Hundred. So the Ford engineer says "lifetime" for the Ford Fusion, while this says 150,000 miles. Looks like that Ford engineer should have read his own service manual.


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## jbfan (Jul 1, 2004)

The truck is a 108 F150, 3.3 engine. 
The owners manual says to check the fluid (if dipstick provided) every oil change.
At 150 K miles, replace the filter and fluid, change rear axle fluid, and replace the drive belts. 
A ME that deals with cars told me to do only 25% fluid change if I do anything with it.


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## chandler48 (Jun 5, 2017)

Just another horror story. I had a '93 F150 and took it to a dealer for full service, including transmission fluid/filter change. Don't ask why. I was over protective, I guess. I got the truck back and it began to shift very poorly, so I pulled into an independent garage to have the transmission fluid checked. The mechanic called me over when he pulled the dipstick. The fluid was brown, not red. The dealership had introduced good old motor oil into my transmission. It got ugly before it got pretty. The dealership eventually had to rebuild the transmission due to inordinate friction wear due to the oil.


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## pwcopy (Aug 27, 2017)

FM3 said:


> "Lifetime fill." What does "lifetime" mean to a Ford engineer? Engineers should know to use actual numbers. "Lifetime fill" is meaningless unless they actually mean lifetime.
> 
> I already posted a link about BMW claiming "lifetime fill" and then the actual manufacturer of the transmission makes a video showing why they should stop saying that and instead change it at 60k. Should people have believed BMW and the sticker on their trans that says "lifetime fill"?
> 
> ...


You are correct and my memory is going south. It was actually the next car I owned, a 2012 Fusion. Here's the manual. See page 354. The first trans fluid changed is advised @ 150k. I guess that's what Ford calls lifetime. At any rate, I'm a follow-the-manual guy. It's served me well.


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## FM3 (Aug 12, 2019)

Since chandler48 wrote a bad dealer story, here's another one, but it's for a manufacturer not merely a dealer. For I think four years, Volvo's owners manual said to use ATF as power steering fluid. That was a misprint. I wonder how many people ruined their power steering from following the manual.

_"JTF is correct - the manual is unfortunately incorrect - Volvo has addressed it with the dealers. The issue is the mixing of fluids. Pentosin ATF and other generic ATF's are not compatible and it may damage your steering rack seals"_


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## HotRodx10 (Aug 24, 2017)

FM3 said:


> I wonder how many people ruined their power steering from following the manual.


If there had been very many, I think we would have heard about it. there's alot with cars that could happen, but never does, because the systems aren't as sensitive as the 'Type A' think they are.

Many owner's manuals specify power steering fluid for the power steering, but I haven't heard of one case where using ATF in the power steering has caused a failure.

Of course, putting motor oil in an automatic transmission is a completely different matter. I've known of a few cases where people have done it, either from ignorance or desperation, and it ended quicklly and catastrophically every time.


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## Drachenfire (Jun 6, 2017)

mark sr said:


> I'd just drain the fluid, replace the filter along with inspecting the bottom of the pan. That doesn't replace all the fluid but IMO the old remaining fluid isn't a big deal.


Ditto. 

This is also what my mechanic (been going to him for almost 25-years) recommends.

Sold my last truck ('00) Silverado) with 265K on it with the original transmission still working perfectly.

My current truck ('15 Silverado I bought in '18) just turned over 100K and no issues with the transmission.


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## SoNic (Feb 14, 2021)

HotRodx10 said:


> Much more than just draining the pan and refilling it, which would only get about 1/3 of the fluid changed


You used 12 Qt of fluid. A drain and refill uses 4Qt.
Do that drain and refill 3 times (separated by some 50 mile drives) and you will get the same result.


FM3 said:


> "Lifetime fill." What does "lifetime" mean to a Ford engineer?


Same as for a Toyota engineer. Pure BS, covered by small print in the manual about "heavy usage".
Any car used in a Souther US city (stop and go traffic in ambient temps at 90F or higher) will fall under that heavy usage.
My RAV4 was getting more that 200F transmission temps in those conditions, and it's the model with Towing Package! Low speed means no airflow to the radiator, stop and go implies numerous shifts, and drive with an unlocked TQ. The Coolant partially cools transmission too.
I added an auxiliary cooler for transmission after that.


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## HotRodx10 (Aug 24, 2017)

SoNic said:


> You used 12 Qt of fluid. A drain and refill uses 4Qt.
> Do that drain and refill 3 times (separated by some 50 mile drives) and you will get the same result.


No, it doesn't, because once the 4 qts is mixed in, the next time you replace 4 qts, you're replacing some of the new, as well as some of the old. No matter how many times you change 1/3 of the fluid, you'll never get rid of all the old fluid. By the numbers, after 3 times of changing 4 qts at a time, you'll still have 3.55 qts of old fluid left in the system. Even after the 4th time you replace 1/3 of the fluid (for a total of 16 qts paid for), there's still 2.37 qts of old fluid in the system. 

Mathematically, your portion of the old fluid left in the system after any number of times you change 1/3 of the fluid is .66667 raised to a power equal to the number of times (.66667^3 = .2963; 12*.2963 = 3.555)


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## SoNic (Feb 14, 2021)

When you do it your way, the fluid mixes too. Is not toothpaste consistency, in a tube, to push the "old" out.
Inside TQ is plenty of "space" for that mixing to happen. The transmission internal pump ensures that the fluid is thoroughly mixed.


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## HotRodx10 (Aug 24, 2017)

SoNic said:


> When you do it your way, the fluid mixes too.


Very little, actually. It was easy to tell when I got to the new fluid.


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## SoNic (Feb 14, 2021)

Same with drain and refill. When you drain the third time (last of the 12Qt), the fluid is looking as fresh as the one in the bottles.
I did it both ways, on many cars (yes, I own old cars, never bought a new one), and now I don't bother with removal of the hose method.


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## HotRodx10 (Aug 24, 2017)

SoNic said:


> Same with drain and refill. When you drain the third time (last of the 12Qt), the fluid is looking as fresh as the one in the bottles.


If you say so. It's only math; it could be wrong.


SoNic said:


> I did it both ways, on many cars (yes, I own old cars, never bought a new one), and now I don't bother with removal of the hose method.


To each their own. I prefer my method for my vehicles; I think it gets much closer to a full fluid change, which I believe is the best thing for my well-maintained transmisssions. Based on what I've read here and other places, if I acquired a vehicle that had not had regular fluid changes for a long time, I'd probably consider changing it a little at a time.


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