: So Mixing Different Weight Oils is OK?



Elmer Fudd
08-21-06, 12:12 PM
Perhaps it is another urban ledgend, but I always thought that mixing different weight oils in the car is very bad (why I dunno, doesn't make much sense does it?).

From what I read here sounds like I was mislead??? :bigroll:

zonie77
08-21-06, 12:31 PM
Funny, I never heard that one.

While I don't recommend it, it shouldn't hurt anything. All oils are supposed to be compatibile. The biggest reason not to do it is you don't know what weight you wind up with.

That being said I occassionally use my odd oil bottles in my old Dakota pickup. It has 185K, runs good and uses very little oil.

Ranger
08-21-06, 06:29 PM
You can mix 10W & 30W to get 20W or you can mix 5W20 & 10W40, but you do not want to mix 10w & 10W30. In other words, it's OK to mix straight weights or multigrades but not straight weights & multigrades.

Elmer Fudd
08-21-06, 08:01 PM
You can mix 10W & 30W to get 20W or you can mix 5W20 & 10W40, but you do not want to mix 10w & 10W30. In other words, it's OK to mix straight weights or multigrades but not straight weights & multigrades.

Gotcha......:thumbsup:

Thanks

ewill3rd
08-22-06, 08:36 AM
You can mix brands but don't mix grades.
The viscosity is controlled by the additive packages of the oils.
Mixing them will give you unpredictable results.
In math 10 minus 5 is 5 but mixing chemicals isn't necessarily based on simple math.

I'd say in a pinch if you can't remember what grade oil is in your car it's better to top it off with something that may not be the same and have some lubrication rather than none, but I wouldn't make a practice of it.

Stick with one thing.
With the availability of oil off the shelf it shouldn't be too hard.
Keep a quart in the trunk if you can.
Make sure it won't get smashed!

Elmer Fudd
08-22-06, 10:21 AM
Yes, I see no reason to mix, I was just curious:rolleyes:

Krashed989
08-23-06, 03:55 AM
You can mix 10W & 30W to get 20W or you can mix 5W20 & 10W40, but you do not want to mix 10w & 10W30. In other words, it's OK to mix straight weights or multigrades but not straight weights & multigrades.


Eeeep.... I accidently mixed 10w40 with straight SAE40 oil in my caddy before... Didn't seem like anything was hurt.... What exactly could happen? We don't have winter over here so the 10w doesn't really mean much to me over here.

ewill3rd
08-23-06, 06:48 AM
It's not so much "what could happen" as it is you just don't know what you end up with.
Like I said you just end up with something that has unpredicable properties.

One of the most important factors of the oil is the viscosity.
They use lots of stuff to control the flow factor, but when you mix chemical bases like that you are going to get unpredictable results.
You might get oil that flows too well, or barely at all.
Either of which can be bad under certain conditions.

Honestly I doubt any damage would occur under normal conditions, but in cold weather you could starve your engine for oil or have oil pressure problems in extreme heat.
Just avoid it if you can.