# Bad radiator cap



## Windows on Wash (Aug 30, 2011)

No. The pressure in the system restrains the boiling in this case. Leave the cap on and change it out when you get home or to the auto parts store.


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## Guap0_ (Dec 2, 2017)

No, don't loosen the cap. Try to find a parts store near work. Hopefully, they will sell Stant caps.


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## Nealtw (Jun 22, 2017)

Have the cap check for the pressure it will hold, this could be symptom of a different problem. Check your oil for gray.


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## papereater (Sep 16, 2016)

Guap0_ said:


> No, don't loosen the cap. Try to find a parts store near work. Hopefully, they will sell Stant caps.


Tanks, Guap! Whats a stant cap? (I can google it but rather get it from a fellow member).


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## mark sr (Jun 13, 2017)

Stant is a well known brand of radiator caps.
While it's possible it could be an issue unrelated to the cap, replacing the cap is a good place to start.


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## SeniorSitizen (Sep 10, 2012)

If it's overheating in the winter with the cap completely off there are other problems.


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## papereater (Sep 16, 2016)

Wow, good to know. Guess that is a good place to start, easy too. Then go from there. I did put in a new water pump (recent thread here). No leaks on driveway, or beneath pump like that old bad one. Car's temp has been behaving goofily (a word??). Temp rises a bit off the "ideal spot", then drops, then rises even more threateningly, toward red zone. 

Thought of thermostat, but for now, seeing oozing/steam from cap I will address that first.


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## Nealtw (Jun 22, 2017)

Check that oil.


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## papereater (Sep 16, 2016)

Nealtw said:


> Check that oil.


Geez, almost forgot! Good ttip. Will do that now! Looking for choc milkshake.......


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## iamrfixit (Jan 30, 2011)

papereater said:


> I did put in a new water pump (recent thread here). No leaks on driveway, or beneath pump like that old bad one. Car's temp has been behaving goofily (a word??). Temp rises a bit off the "ideal spot", then drops, then rises even more threateningly, toward red zone.
> 
> Thought of thermostat, but for now, seeing oozing/steam from cap I will address that first.



Sounds to me like you have air in the cooling system. These are all symptoms that would make that seem very likely. 

Does your vehicle have specific cooling system bleeding procedures? 

Were those procedures followed?

Some vehicles are very difficult to get all the air bled out, those with radiators mounted lower than the engine or reverse flow cooling systems may require vacuum filling to get all the air out. It needs to be taken care of right away, you are at risk of cracking a head, if that hasn't happened already. That's a very expensive repair.


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## Nealtw (Jun 22, 2017)

papereater said:


> Geez, almost forgot! Good ttip. Will do that now! Looking for choc milkshake.......


 Gray slime.


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## Brainbucket (Mar 30, 2015)

SeniorSitizen said:


> If it's overheating in the winter with the cap completely off there are other problems.


That's correct for old school vehicles that run 160-180-195 degree thermostats but todays vehicles run at higher temps than the 70 Chevelle. Most vehicles today that have electric fans that turn on at 220-230 degrees. Boiling point is 212. So they use the pressure to raise the boiling point. So you can't 'loosen the cap' as it will boil out the radiator. That's why you see it leaking out the cap as the boiling point is reduced and it wants out. Replace the cap. I use either the dealer or Stant. Stant is a good brand of cap. NEVER remove the cap when cooling system is under pressure. A good way to test is you can remove the cap is to squeeze the radiator hose. If it is hard and hot, it's under pressure. If you can squeeze the hose and it isn't burning your hand, you can remove the cap, SLOWLY! Instant steam will peel your skin right off you. I have seen it happen and it's nothing nice.:vs_cool:


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## papereater (Sep 16, 2016)

Thanks, people. Turned out the oil is "clear", no milkshake, or grey slime, or Starbucks coffee/latte smoothie. So, I went to AZ with friends car, and they looked at my cap and I felt dumb, as it is not the rad cap, but the thermostat housing cap. Sheesh. None in stock. They ordered it to arrive at my AZ closer to home later today, though. After 32 years of ownership I would remember, but not so. 

I called it the rad cap because I always fill rad system through this cap. Oh well......


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## papereater (Sep 16, 2016)

iamrfixit said:


> Sounds to me like you have air in the cooling system. These are all symptoms that would make that seem very likely.
> 
> Does your vehicle have specific cooling system bleeding procedures?
> 
> ...


My haynes manual does not specify any bleeding, as far as I can remember. I have done this before many times (after 32 years) with no hick ups. But one never knows- mistakes happen. Maybe there IS a pocket of air. I will review that manual again at home, to be sure. Thanks for the tip.

The heat never did reach the red zone, if that helps, just headed in that direction. I do watch that needle very closely, and even installed a on/off toggle to turn fan on in case. It works. But yes, one must beware.


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## papereater (Sep 16, 2016)

I will use same old bad cap with rotted blackish goo, but line it with thin teflon sheet, carefully cut out to fit (have some here at work). Figure that should help as rotten rubber surface then would not be in contact with the housing. If no one has any objections to this easy short term fix to get me home, I will proceed. Speak now or forever hold your peace. LOL.


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## Dave Sal (Dec 20, 2012)

You have a cap on your thermostat housing? Sounds odd. Or is it an expansion tank? I have one in my car, and it needs to be filled to the correct level. Fill it too high and there is no room for the coolant to expand and you risk blowing out parts of the cooling system from too much pressure.


What kind of vehicle is this?


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## iamrfixit (Jan 30, 2011)

Check your owners manual and the underhood tags, if there is a bleeding procedure it will usually have info in both those places.


Don't know if the teflon will help much. Careful, you don't want pieces to come off and end up in the coolant, might plug up tubes in the radiator or heater core.


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## papereater (Sep 16, 2016)

Dave Sal said:


> You have a cap on your thermostat housing? Sounds odd. Or is it an expansion tank? I have one in my car, and it needs to be filled to the correct level. Fill it too high and there is no room for the coolant to expand and you risk blowing out parts of the cooling system from too much pressure.
> 
> 
> What kind of vehicle is this?


Sorry, after 32 years of ownership I think its like a part of my body and no need to mention it, but it is a Pontiac Sunbird GT, 1987, non turbo. Yes, it is a therm housing and not an expansion tank, which I also have.


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## papereater (Sep 16, 2016)

WEll, that teflon sheet fit perfectly. Now to drive home...........


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## mark sr (Jun 13, 2017)

Some vehicles are prone to getting air pockets in the cooling system. Both my current jeep and the one I used have are that way. Makes flushing the radiator and changing the coolant more difficult than it should be.


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## papereater (Sep 16, 2016)

Made it home no problem, although, temp went , again, higher than normal, BUT this is no where near the red zone this time. my teflon sheet held up great! No spillage!

Going to p/u my new cap tomorrow, but I dont trust for beans my T stat, so Im going to place in water, heat it up, and watch the temp on a thermometer when it opens up. Then watch it close and note temp. Not sure the spec for my car, but will check my manual. 

I know theyre cheap, but hate to guess/throw away $$. I will advise asap.......

Will also check for how to add coolant.


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## SeniorSitizen (Sep 10, 2012)

papereater said:


> but I dont trust for beans my T stat, so Im going to place in water, heat it up, and watch the temp on a thermometer when it opens up. Then watch it close and note temp.


 **********************************************
A word about checking in water. This happened to me on a 65 ford when I was a pup. 

Loosing about a gallon of water every time I drove it. How did I know. It was cold and the heater wouldn't work. Took stat out, checked in water and sure enough it was open all the way when the water was very hot so assumed it was good. Not really, because that stat should gradually open as the water heats.


If it sticks like mine did and slams from fully closed to fully open with boiling water or a greater temperature, out goes a gallon from the overflow. No puke jugs then, goes on the ground and can readily be seen.


Save yourself possibly a big bundle of money by spending a few bucks on a new Stant thermostat that's recommended for your Pontiac.


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## papereater (Sep 16, 2016)

OK, Senior, youve convinced me. Good to know other peoples experiences. It's such a pain installing one anyway, might as well pop in the new one. It's been years. But, for the record, I will (and for fun) check the old one with a thermometer. That way, even with a new one in I will know if the old one was the cause........

I hope I can get this old one out.


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## papereater (Sep 16, 2016)

Came out easy- then I boiled it. It opened late, meaning it opened at about 96 deg C, (or about 208F. Maybe thats why the thermostat cap was spitting coolant(?). That thing can take only so much pressure, I figure. Anyway, it was old and have new housing cap now. Waiting for T stat tomorrow, and yes, I will boil it too, along side the old/bad one, just to see. 

What else do I have to do????????


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## ChuckF. (Aug 25, 2013)

T-stats usually have the opening temperature stamped on them somewhere. 

Make sure the tube from the radiator neck to the overflow tank doesn't have a small leak. if it does, coolant can dump out into the overflow and most of it will make it past the leak and go into the tank, but when pressure drops and it tries to suck it back it will not be able to because of the small leak. That means you end up with air in the cooling system.


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## Guap0_ (Dec 2, 2017)

If you replace the Tstat, do not buy Fail Safe from AutoZone. Any other brand is ok. Stant is the best.


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## mark sr (Jun 13, 2017)

Guap0_ said:


> If you replace the Tstat, do not buy Fail Safe from AutoZone. Any other brand is ok. Stant is the best.



Why? I've bought several from AZ. I did have one fail but as it's supposed to it failed open and if I remember correctly it was covered by a 1 yr warranty.


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## Guap0_ (Dec 2, 2017)

I had one of them fail too. I don't care about the $5 warranty. I don't want to have to do the job twice in the middle of winter.


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## mark sr (Jun 13, 2017)

What's a $5 warranty?


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## Guap0_ (Dec 2, 2017)

That's the cost of the T Stat. I'm not going to buy an inferior brand just because of the warranty. I stay away from that company. A friend of mine won't even shop at AutoZone at all.


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## mark sr (Jun 13, 2017)

I've had very few issues with AZ and when there is an issue they stand behind the warranty better than most of the local competitors.


Going back to the fail safe thermostats, the only failure I've ever had was the 1st one I installed in my ford 4x4 - it died within a week of installation, it's replacement has worked fine for 5 yrs or so. I don't know how many yrs ago I put one in my tractor.


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## Guap0_ (Dec 2, 2017)

I had the same problem. It died a week later. Never again.


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## papereater (Sep 16, 2016)

i will have to check my receipt if it was a failsafe, it was the one that costed a bit more and was available sooner, so I ordered it. 

But anyway, wanted to let yous know popped all back in and drove to work this morning with no problems like I had Friday. So far all is good. Now, to find my ac leak. Warmer weather is here! (yes, my 32 year old car still has working ac!)


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## Brainbucket (Mar 30, 2015)

I hate auto zone. Yeah, they have a warranty from hell and it's their selling point. They buy crap by the train loads that no one else wants and sell it to the public. Sure, life time warranty but you will wear out the bolt holes replacing the warrantied part. I once put 7 alternators on a crown vic from auto zone that the customer supplied. After the 7th one, auto zone called me and said I didn't know what I was doing. I said come on down and show me. What they didn't know was I had already got one from NAPA and installed it and it worked fine. Plus I had already tested to make sure power and the ignition power was there. They came down with their 'book' and proceeded to explain to me how to do this and their alternator didn't work. They said it's something with the car. As they are arguing with the owner, I installed my alternator and started the car and vola, 14.3 volts and the amps were there. I then told those bozos that they were bozos. I asked them what training did they have. None, just direction from the auto zone book. Then I told them the years of training I have. They left and I never had a problem with them again. If I said their part was bad, they said ok and I would replace it with a real part. I HATE auto zone. NAPA, O'Reilly, and the dealer are the only places I go now. I have just started using Rock Auto. I get the part numbers from NAPA and see if Rock Auto has it and compare prices. Rock Auto it usually cheaper but it take a week to get here. The customer doesn't care how you repaired their vehicle, they just want it fixed the first time. You put a defective part on there car to save a few cent, there it fails, the customer isn't mad at the part. They are looking at you. Bad parts make for bad business. :vs_cool:


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## mark sr (Jun 13, 2017)

> they have a warranty ... and it's their selling point.


But their warranty is a big selling point especially to diyer! I tend to keep vehicles a long time and they stand behind their lifetime warranty. I've replaced brakes multiple times on several vehicles but only paid once. I especially like their computerized warranty records. While there are a couple of other local auto parts that do the same - they seem to loose [or maybe erase] the records after a yr or so.


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## papereater (Sep 16, 2016)

Fair points from Brain above. But one good book I read a while ago, The Coming China Wars, here:

https://www.amazon.com/Coming-China-Wars-Revised-Expanded-ebook/dp/B004M18MIA

explained about counterfeit parts- where even the distributors can not tell between an authentic brand and the fake one. Until it is too late. One example was brake shoes on a school bus, shattered, killing students. Anyway, I bet even Napa gets counterfeit parts sometime.


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## mark sr (Jun 13, 2017)

I've been having trouble buying quality points for my tractor. The last 2 times I went to NAPA they sold me ones made in Mexico :sad: the cheaper points have replaced the fiber [?] tab that runs on the lobe of the distributor with plastic that either wears out prematurely or breaks.


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