It's OK to mix engine oil brands, types, and viscosity...

[ka9mnx]

Originally Posted by Matagonka
There's a few guys here arguing that it's dangerous because you're mixing oil properties, blah blah blah.

I don't believe it one bit.

It's not dangerous but it's also not optimum.

 

[kschachn]

Originally Posted by Matagonka
There's a few guys here arguing that it's dangerous because you're mixing oil properties, blah blah blah.

I don't believe it one bit.

Can you provide links to these "blah blah blah" posts that say it is dangerous? I haven't seen anyone on here say it is "dangerous" but perhaps I haven't read every post. In fact, ASTM D6922 is there to make sure it is not dangerous. But is danger your only consideration?

What I have seen are posts that show the "W" rating of the oil is not necessarily preserved, which is correct. I have also seen posts (mine included) that point out the resulting mixture will have no guaranteed approvals, specifications nor certifications which is also correct. Once you start your ad hoc mixing, you are now the blender rather than the manufacturer. There is no guarantee it meets any of the specifications each individual oil met and in fact it is likely it will not.

But is it dangerous? No, that is hype.

 

[PimTac]

The only way to know would be to run a long term test running a single brand in one engine and a mish-mash in the other. Will the engine blow up? Probably not but it would be interesting to see the cleanliness and wear of the mixed oil engine after 100k or 150k.

 

[y_p_w]

Originally Posted by kschachn
Originally Posted by Matagonka
There's a few guys here arguing that it's dangerous because you're mixing oil properties, blah blah blah.

I don't believe it one bit.

Can you provide links to these "blah blah blah" posts that say it is dangerous? I haven't seen anyone on here say it is "dangerous" but perhaps I haven't read every post. In fact, ASTM D6922 is there to make sure it is not dangerous. But is danger your only consideration?

What I have seen are posts that show the "W" rating of the oil is not necessarily preserved, which is correct. I have also seen posts (mine included) that point out the resulting mixture will have no guaranteed approvals, specifications nor certifications which is also correct. Once you start your ad hoc mixing, you are now the blender rather than the manufacturer. There is no guarantee it meets any of the specifications each individual oil met and in fact it is likely it will not.

But is it dangerous? No, that is hype.

Obviously it's not ideal. And it's been noted that an oil change can leave anywhere from 5% to maybe even 30% of the previous oil in there. However, I've tried assorted mixtures besides just what's still in the sump because I was short a half quart. I've topped off with a different blend.

But of course the fluid change that has the smallest proportion of fluid removed is almost always an automatic transmission. You'd be lucky to get 40% out of there. Yet people change fluids, have no idea what the factory fill is, and sleep well at night.

 

[Garak]

Originally Posted by OVERKILL
I'm interested in the source of that claim. That's like an engine with a 5L sump only draining 3L of oil and taking a 3L change capacity. I don't believe I've ever run across that. About the closest I can think of would be the old double-hump Ford oil pans where somebody neglected to drain the front part of the pan, but even then, that wouldn't be 2L of oil.

I think the RX-8s were leaving behind two litres. I don't think the G37 leaves too much behind, but one can always follow my procedure and try to keep as much of the same product on hand and of the same lot number as possible for many consecutive oil changes.

 

[Shannow]

Originally Posted by y_p_w
But of course the fluid change that has the smallest proportion of fluid removed is almost always an automatic transmission. You'd be lucky to get 40% out of there. Yet people change fluids, have no idea what the factory fill is, and sleep well at night.


Congratulations...you have won the strawman of the year award so far for 2019.

Firstly, this is a discussion regarding the mixing and compatibility of...engine oil...in an engine oil forum, discussing...engine oil.
Secondly, ASTM D6922 is described...by the ASTM as
Quote
Standard Test Method for Determination of Homogeneity and Miscibility in Automotive Engine Oils


Quote
1. Scope

1.1 This test method covers the determination if an automotive engine oil is homogeneous and will remain so, and if it is miscible with certain standard reference oils after being submitted to a prescribed cycle of temperature changes. This test method is very similar to the homogeneity and miscibility test described in FED-STD-791/3470.1.


So it takes an engine oil, mixes it with 7 reference oils, heats it and cools it and they are not allowed to split or blow chinks...that's it.

I've got the standard, and it in no way suggests that two or more ATFs, unrelated to any engine oil, being mixed in a tranny, of ill determined type specification in any way infers any compatibility or miscibility of completely unrelated fluids in completely unrelated compartments (engines).

The fact that you can mix Vodka and Orange juice, in any proportion and help you sleep at night is only marginally less relevant.

 

[Shannow]

Originally Posted by kschachn
Originally Posted by Matagonka
There's a few guys here arguing that it's dangerous because you're mixing oil properties, blah blah blah.

I don't believe it one bit.

Can you provide links to these "blah blah blah" posts that say it is dangerous? I haven't seen anyone on here say it is "dangerous" but perhaps I haven't read every post. In fact, ASTM D6922 is there to make sure it is not dangerous. But is danger your only consideration?

What I have seen are posts that show the "W" rating of the oil is not necessarily preserved, which is correct. I have also seen posts (mine included) that point out the resulting mixture will have no guaranteed approvals, specifications nor certifications which is also correct. Once you start your ad hoc mixing, you are now the blender rather than the manufacturer. There is no guarantee it meets any of the specifications each individual oil met and in fact it is likely it will not.

But is it dangerous? No, that is hype.


There have been a couple of instances where it was reasonably widespread and catastrophic.

The count that I've been able to find in data is a count more than a male groin, and less than the standard number of fingers on a hand.

Extremely rare that it causes a major issue.

But the reductions in the "W" performance that have been identified will never affect anyone who isn't needing the extremes of their W rating...and the one or two that get a bad brew will have a bad start one winter, never associate it, and never thus "make the news".

The "nothing blew up" standard of performance that is the posterchiled of 2018-19 BITOG is well and truly met to the 99.999999% percentile.

But still the Myage defence still stands...."the best defence is no be there"

Disclaimer....do I mix ?
Yes...I can't find a place to park my cars that gets below -11C, and that's a new record, 4C colder than I've ever parked a car before (and the -7C was a 25W that still started just fine)….I couldn't break an oil bad enough to have a problem.

Do I recommend, across the board (per the OP) that mixing is a sound practice, on a board where members have in the last few weeks been starting their cars at -40C as recently as two weeks ago ?

OF COURSE NOT !!!

 

[OilUzer]

Last time I mixed vodka and orange juice I got a screwdriver

We need a PhD in chemistry and physics to explain that!

This subject comes up often.
I mix leftover engine oils here and there but know (from bitog) that it's not the best idea especially in very cold temps which does not apply to me.

It may be hard to accept/digest but unless if you have some data and/or proof to the contrary, best is not to refute the existing studies, research and experts ...

Conclusion:
Just do it but don't argue