Explain why it is bad to mix 2 different oils?

[lipadj46]

Originally Posted By: friendly_jacek
Originally Posted By: AEHaas
For example, most oils have ZDDP as one additive (it actually performs several different functions). A few have none at all. Instead, other combinations of different additives perform the multi duty ZDDP functions. If you mix half of each type of oil together then each ones special formula concentration is cut in half and may not work at all.


Now, which exactly are the ones without ZDDP, so I will avoid mixing them ;-)


I guess I meant low ZDDP.

 

[Norm Olt]

I've not yet seen a bottle of oil that warns the consumer not to mix it with any other oil... Maybe a quart of "SA" has this warning.

As to whether absolute maximum performance is present for either of the two (at least) in the mix, I seriously doubt whether there is a serious denegration of either. Only M (very) HO!

Maybe it could be inferred by OA results, but I think there is sufficient "slop" in any of those numbers to skew accurate analysis.

In short, "REALLY DURN GOOD!" performance can be anticipated.

For my money, a couple of quarts of, say PP 10W-30 (at a $ a quart, after rebate) added to 4 quarts of $1/quart 10W-30 GF4 Formula Shell (or $0.49/quart Chevron Supreme) might well be a better performing oil than 6 quarts of a name-brand, advertised semi-synthetic.

Will it OA as being "better"? I don't know.

Will the engine be well-lubricated? I'd say a resounding "Yes!"

Cheers!

 

[JohnBrowning]

It is not an issue today! You can mix away. IN fact Terry Dyson offered a service for a while where he told you what oils to mix together based on his long running data base of both products and vehicles UOA's....The idea was to create a semi-custom blend for you application using off the shelf products.

We have seen some crazy blends on this site over the years and in not one single case of someone blending 4 or more different oils have we seen it do any harm!!! In fact the UOA always come out just fine. So if you want to blend go for it!

 

[CharBaby]

35 or something years ago, I used to mix my @$$ of with different oils in my old beaters. I didn't have any money and my beaters still needed oil changes and an occasional qt or 2. Most times I would change the filter every other time. I would use any oil and any grade. Ran the HE-doubletoothpicks out of my cars.

Today, with all of the oil specials(closeouts, sale/rebate, FAR etc.) I have quite a large stash of different brands/grades, dino/syn oil and I still mix a little but only based on the season. For example: Summer - 3 qts 5W30 & 2 qts 10W30(those 2 qts maybe/may not be synthetic) but, they're deffinatly different brands.
Winter - 3 qts 5W30 & 2 qts 5W 20/30(same as above)!

I have never had any oil related engine troubles and I've put many hundreds of thousands of miles on my vehicles. I really don't think that the engine cares as much as people do!