Mixing Oils

[hi-miler]

I've read this too many times and would like to see what some of the "experts" say. Over the years by some very reliable sources, I've been told that you can't always get what you desire just by mixing two or more items at what you believe to be the right amounts. The best example I can think of was being warned away from 10W40 oil back in the 80's because it had twice the viscosity indexers as 10W30, and that was bad. So what happens when you mix say 5W20 with 15W40? Or how about 3 quarts of 10W30 with 2 quarts of 30W?

 

[cweed]

I'm no expert, but what you heard is true, mixing two different viscosities doesnt always yield an in-between value that you expect by calculating the numbers and amounts. This is especially true when mixing oils with very different properties, such as two different brands. The best and only way to know what viscosity you got from mixing your oils is to get the oil analyzed.

 

[mikemc]

It would be best to ask this question of a chemist, but I am sure that today's motor oils are carefully blended to perform as-is and that mixing them may not yield a desired outcome.

 

[Last_Z]

As far as viscosity goes....it would be hard to tell exactly. As far as additive clashes and all the other myths.....nonsense.....go ahead....mix happy!
There are quite a few reports on homemade brew that in most cases did as good as any formulated oil.....in a few cases, it did better than expected!

 

[TC]

"Can I mix different viscosity grades of motor oils? Yes. It is always advisable to not mix motor oils, however, different viscosity grades of the same motor oil are compatible. Be aware that mixing viscosity grades will turn out a product that is different in viscosity than either what was originally in the engine or what was added."
http://www.chevron.com/prodserv/nafl/auto/content/faq.shtm

 

[Last_Z]

quote:

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Originally posted by TC:
"Can I mix different viscosity grades of motor oils? Yes. It is always advisable to not mix motor oils, however, different viscosity grades of the same motor oil are compatible. Be aware that mixing viscosity grades will turn out a product that is different in viscosity than either what was originally in the engine or what was added."
http://www.chevron.com/prodserv/nafl/auto/content/faq.shtm

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That's legal talk. Basically, what they are saying is that if you mix and you end up with a higher or lower viscosity and your engine fails (which I doubt would be oil related), neither Chevron nor the vehicle manufacturer will be responsible