Mixing different oils

[Joe90_guy]

OCP stands for Olefin Co-Polymer. They are made by polymerising ethylyene and propylene. If you over-do the ethylene, then the OCP has a tendency to become crystalline at very low temperatures and quiescent conditions. As a result, they tend to need more Pour Point Depressants to meet the MRV spec. However the real problem with high ethylene OCP is that sometimes, even when it passes all of the tests (including MRV) it can still gellify the oil in the field. Many years ago, I recall seeing a letter from Oronite relating to an incident in Hokkaido, Japan where this kind of thing happened.
In my experience, blending different oils made from high and normal ethylene OCP VIIs doesn't cause compatibility issues with HTHS, KV100 and CCS. MRV I'd say was also compatible but I wouldn't stake my life on it!

 

[Garak]

Originally Posted By: Shannow
Guess I've got some humble pie to start on.

Don't grab your fork too fast. The miscibility standards still are what they are, and we do know that some oil chemistries are vastly different then others, albeit still technically compatible. We also know that you can't mix a 15w-40 CJ-4/SM and a 0w-20 SN/GF-5 and have anything that meets any of the specs of either original product.

And, for cold weather numbers, given my climate, I'd rather have an oil that's actually tested to meet the cold weather numbers it claims, particularly with MRV. Then again, if I'm really terribly worried, a pan heater does the trick, as does my heated garage.

 

[Pontual]

Originally Posted By: Joe90_guy
If you blend two oils of identical viscosity grade, then absolutely yes, you will get a mix that is the same (eg 0W20 + 0W20 = 0W20).

If you blend two different oils but which share a similar 'end', then the similar 'end' will not change but the dissimilar end will (eg 0W20 + 0W40 = 0W30-ish and 0W40 + 10W40 = 5W40-ish).

The 'ish' is there to convey that what you get depends on the ratio in which you comingle the oils. Obviously 99% 0W20 + 1% 0W40 will very likely result in a slightly heavier but still on-grade 0W20.

Regarding additive packs, if you blend a 50:50 mix of one oil that contains 10% DI and another with 6% DI, you will end up with an oil containing 8% DI. This gets tricky because 50% API SL + 50% API SN doesn't give you 100% API SM (would that life was so simple!). So, no, performance doesn't automatically blend. Having said that, if you blend a OW20 GF-5 oil with a 5W20 GF-5 oil, then you will get something that very likely GF-5 performance (albeit not demonstrable because there are no specs for 2.5W20 oil).


I agree with most that you posted, but:

If you mix 0w20 with 0w40, you may not get 0w30, because the less VII will be more spreaded in the fluid and won't break the viscosity fall with the same performance. You may endup with a lower grade than a 30 at op temperature.