# What's wrong with 10w-40 in a lawnmower?



## Toller (Jan 2, 2013)

All the lawnmower companies have the same recommendation; 30 unless you need to start in cold weather, and then 10w-30. But 10w-30 will be consumed over 80 degrees.

Why not 10w-40. No one recommends it and one says it will damage the engine. Why?

(I have just bought 30, but am still wondering...)


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## joecaption (Nov 30, 2011)

None of my 3, mowers suggest 30 W oil.
All say 10W30.


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## PoleCat (Sep 2, 2009)

Non detergent 30W regardless of temps.


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## Windows on Wash (Aug 30, 2011)

I run synthetics in mine. Especially the air cooled ones. Higher smoke points.


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## rusty baker (Feb 13, 2009)

Detergent oils like 10w40 will foam in a lawnmower. When they foam, they don't lubricate very well and will lead to failure. That's why non-detergent is specified.


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## Toller (Jan 2, 2013)

http://www.briggsandstratton.com/us/en/support/faqs/engine-oil-recommendations
http://www.snapper.com/us/en/support/faqs/what-oil-type-is-best-to-use
http://www.toro.com/en-us/customer-support/Pages/faqs/mowers.aspx#faq-22

Two specify detergent (the third implies detergent); all recommend 30 unless used below 40 degrees.

So, why not 10w-40?


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## 47_47 (Sep 11, 2007)

My guess...

Most lawn mowers do not have a pressurized oiling system and 10W40 may be too thick to gravity flow / splash through the smaller oils passages.


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## rusty baker (Feb 13, 2009)

Toller said:


> http://www.briggsandstratton.com/us/en/support/faqs/engine-oil-recommendations
> http://www.snapper.com/us/en/support/faqs/what-oil-type-is-best-to-use
> http://www.toro.com/en-us/customer-support/Pages/faqs/mowers.aspx#faq-22
> 
> ...


I guess they have changed. All three of the mowers I own specify non-detergent.


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## SeniorSitizen (Sep 10, 2012)

The spread between the numbers is created with polymers and polymers aren't a very good lubricant so the polymers are held to a minimum when possible.


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## killerformula (Jun 11, 2009)

I don't think there's anything wrong with that oil in a lawnmower. Won't hurt anything.

the reason 30W is specified is that the lawnmower runs at a constant RPM, in a pretty static environment and probably runs pretty hot. There isn't a cold startup phase like a liquid cooled engine running in the winter. So you just don't need a low low viscosity startup. Doesn't mean it will hurt if you do have one.

If you look at the temperature ranges that 30, 10-30 and 10-40 are used they're all fine for your motor. Use whatever is in the garage.


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