Mixing SYNTHETIC oils

[Mystic]

I know that conventional motor oils can be mixed, although I would use only one brand at a time in an engine.

But what about mixing synthetic oils? Mobil a long time ago was saying that people should not mix Mobil 1 with another brand of synthetic oil. Of course, maybe most synthetic oils are probably now Group III. If I used Mobil 1 this winter but I decide to go with Pennzoil Platinum is it okay to switch to the PP even though some Mobil 1 will be left in the engine. Or would it be better to do a conventional oil change first, separating the Mobil 1 and Pennzoil Platinum oils from being directly mixed?

 

[blupupher]

Don't ever switch! Your engine will blow up!

Seriously, switch away and don't look back.

 

[TimVipond]

I've never heard of any problems switching from one oil to another in the course of a normal oil change. Most companies do not recommend and usually discourage random mixing of oils, such as a quart of 5 completely different types of oils for one oil change. Some companies suggest that if you are on the road and a quart low, it is best to add a quart of another brand and then do a complete oil change at your earliest convenience.

 

[ekpolk]

I'll defer to the real chemists on this, but years ago (as in the early 70s IIRC), there were problems mixing certain types of synthetics with others and mineral oils. To my understanding, there were several diesters (dare I call them primitive???) which, when combined with natural hydrocarbons or PAOs, would react and solidify into a sticky, gooey unpumpable mass. From what little additional info I've been able to scrounge up, I assume that diesters with this unfortunate characteristic are long gone from any real-world motor oil forumlae.

 

[TimVipond]

Yeah, the early and mid 70's were a trying time for synthetics. Incompatabilities were common place with oils, sealants, gaskets and o-rings. I'm not aware of any problems in the past 20 years.

 

[warchildindy]

We have a 2004 base acura rsx with a 2 liter v-tec engine. I used amsoil xl 5w-20 in a first oci and have been using Mobil 1 5w-20 synthetic without flushing for the last (2) oci's. I always thought that these (2) formulations were very close anyway.

I am also planning on using Pennzoil platinum 5w-20. Should be close to the same formulation as the other (2) previous oils mentioned. It's cheaper and also easy to find.

 

[Triple_Se7en]

I've read a few publications here that don't recommend mixing synthetic brands. Unfortunately, I never thought to save the websites for threads like these. I mix conventional oils a couple times each year - out of around 14 annual oil changes I engage in - having five vehicles in my driveway. Two of those vehicles use synthetic-only, but neither one sees a mix of brands.

 

[WishIhadatruck]

I don't know what the risks are, if any. I have mixed my last 2 oil changes in one of my cars. I have used 3.5 qts of Mobil 1 5w30 and 1 qt of Castrol Syntec 5W-50 and that mix gave me a better UOA than just Mobil. It certainly doesn't seem to be hurting anything.

 

[wgtoys]

I wouldn't worry even a little about switching brands at oil change time.

 

[Blue99]

Switching oil should pose no problems, but I would suggest caution when mixing home brews with "synthetic" on the label.

By far, the majority of API licensed motor oils, with "synthetic" on the label, are blended from Grp III base stocks. Lately, we've seen reports that indicate additives have to matched to individual Grp III base stocks.

So a mix of brand A & brand B synthetics may lead to a homebrew where one of the major additive functions, performed by friction modifiers, dispersants, pour-point depressants, etc. is not working in the home brew.

 

[Triple_Se7en]

Quote:

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Switching oil should pose no problems, but I would suggest caution when mixing home brews with "synthetic" on the label.

By far, the majority of API licensed motor oils, with "synthetic" on the label, are blended from Grp III base stocks. Lately, we've seen reports that indicate additives have to matched to individual Grp III base stocks.

So a mix of brand A & brand B synthetics may lead to a homebrew where one of the major additive functions, performed by friction modifiers, dispersants, pour-point depressants, etc. is not working in the home brew.

---

This above is very similar to what I've read. The risk-factor "with some" appears to be shorter-than-expected oil life with a product that's generally intended for longer life.

Some may do alright mixing - some may not. As always... if you want to do more than just one synthetic-mix, get a used oil analysis done. If doing only one, you run the risk of premature depleted oil. The harmful effects mixing dinos is more minimized ...ie.... shortened OCIs & better mix-acceptance percentages.