SAE Oil weights

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cory

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You engineer types: say a car needs a quart of oil added and it calls for 5w-30, you only have a different weight handy, say 15w-40, does it cause problems to use the alternate weight or is that taboo?
 
Smaller oil passages and closer bearing tolorences probably dictate thinner oils. Pardon my spell'n.
 
15 40 is a lot different than 5 30.

I agree with Chris, if you NEED to it would be better than running out of oil. Running the correct oil is important. Not to mention that 15 40 is a "C" designation for compression ignition and your 5 30 is a "S" designation for spark ignition. One is for diesels and one is for gas engines.
 
I've been running my kubota for 10 years with 15w40, I read recently I should have used 5w40 which I actually put in today. Is that ok?
 
Not being familiar with 5 40 I looked it up. It is a diesel grade oil and has the "C" designation.

The only difference is that you will have better cold oil performance. Maybe not a bad idea during winter time. Not sure how cold it gets in France this time of year.

Nothing wrong with it at all. It will have the same characteristics as 15 40 when hot, just be a little thinner when cold.
 
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All interesting replys, gracias.

Guess I better stock the right earl.
 
Probably the best idea Cory. It is not like you will cause immediate harm to an engine by running the wrong oil, but in the long run the right oil will pay for itself. At least, it is best to run "C" spec oil in a diesel and "S" spec oil in a gas burner. There really is a lot of difference in additive packages properties of the oil.

Adding a quart is not the end of the world, but overtime increased engine wear and reduced fuel economy will result.

If an engine is designed to run with 5w30 and is run with 15w40 the bypass will be open for much longer when cold and let unfiltered oil circulate. It also takes more energy to pump the heavier oil causing reduced fuel economy.
 
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Understood. Good info
 
15 40 is a lot different than 5 30.

I agree with Chris, if you NEED to it would be better than running out of oil. Running the correct oil is important. Not to mention that 15 40 is a "C" designation for compression ignition and your 5 30 is a "S" designation for spark ignition. One is for diesels and one is for gas engines.
Double check that. That varies by brand.
 
Something else to keep in mind different weights also can have different additives, even in the same brand, that don't always interact well together.
As Jim said, in a pinch, to get you home, sure, but change it as quick as you can!
But that is what I was taught, doing some research just now it seems it's just fine to do so?
 
Yeah, interesting.

What I just read stated that almost all "c" spec oil carries the corresponding "S" spec too. I take that to mean that if 15w40 "C" oil carries the "S" spec you can use it in your spark ignited engine if 15w40 is recommended. Sheeeeit.

The opposite does not seem to be true for "S" spec oils. The do not carry the "C" spec as well.

I believe that there is way more zinc in diesel oil, which is bad for catalytic converters. Makes me wonder why they would recommend C spec for gas engines. i have not seen a gas engine call for 15w40 in a long time though.
 
We ran a leaking Honda accord on a mix of differential oil and bar oil to get home one say from high school. We didn't make it home by the way. The ummmm, engine locked up or threw a rod or something.
 
Funny how things work out like that. We had to pee and pour beer into a radiator to get home one night. It's stunk, be made it home!
 
I run synthetic motor oil in almost everything I own. My Dodge pickup with the Cummings I run Valvoline 5-40 all year round. Used to run Petro Canada Duran 5-40 but like the Valvoline.
In the wife's mini van Castrol Syntec 5-30 .Castro Syntec 10-30 in the chipper and stump grinder gas jobs.
Lawn mower , snow blower, power barrow 30W non detergent..
 
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