Soooo, OK to mix fluids? which?

[e9999]

well, don't know about you, but me, being the unprepared ad-hoc type ( ) will probably always end up changing brands, looking for the better one (or the great sale).
So, I find myself often having a bunch of remnants around. Like buying a couple of 6 qts jug of oil and having 4 qts left which is not enough for another change etc etc.
Kinda piling up and there is only so much needed for the lawnmower etc.
So was wondering, when is it OK to mix brands and types, generally speaking?

- coolant: from reading here, I take it don't mix green and Toy red. Easy to be consistent. I only use red.
- engine oil: what's with that? I guess don't mix dino and syn, perhaps. But what about brands within a certain weight, as in add some brand Y 10-30 to existing brand X 10-30. That OK or problematic? How about different weights?
- gear oil? same?
- ATF and PS?
- Brake?

any general rules or good info?
thanks
Eric

 

[GXO]

Generally speaking:

- don't mix dino and synth.
- don't mix ANYTHING with brake fluid
- don't mix ANYTHING with coolant
- ATF or PS Fluid...don't mix

Don't mix anything if you can help it. Motor and Gear oil are the only places I would even consider it.

 

[RavenTai]

if you mix motor oil shorten the interval by half or more, different brands use different additives to do the same job, some can clash and defeat each other leaving the oil unprotected

For best practice you should pick a good brand of fluid and stick with it

I use remnants in the lawn mower, as chain saw (90wt and oil mix makes good bar oil) , give to my neighbor cause he always runs out, as cutting fluid air tool oil ect ect it always finds a home somewhere

 

[firetruck41]

I don't mix anything if I can help it. I had to buy a different brand, quart of oil to add one time. But since I have a little oil consumption, I always buy enough oil to have a couple quarts on hand, and usually take a qt with me if I am taking a long trip.
The tranny fluid is mixed with whatever residual was in there, but eventully after a few changes it will be largely mobil one.

 

[e9999]

agreed it's probably better practice to not mix stuff, but not obvious how bad the practice would be in reality. Is it really clear that 2 brands of same weight, same rating oil are automatically incompatible? I would say unlikely these days. (Playing devil's advocate...)

Let's keep also in mind, though, that the typical bleeding, refilling, etc, practice probably mean that you end up mixing stuff anyway, like it or not, unless you "waste" large amounts of extra fluid. I doubt that a draining or bleeding procedure gets rid of of all the previous stuff. How come nobody is worried about adding only 4 qts of different ATF to the sump, but mixing PS would be so bad, eh?

just wondering...
E

 

[RavenTai]

because it is a lot easier to get all the PS fluid out, getting all the atf out of a tranny it not a simple matter for the DIY guy, the best I can (cheaply/easily) do is 4 qts in the tranny every oil change eventually it will be mostly new fluid, another thing to consider is what fluid is already in the truck is beyond your control, to me that is different from purposefully mixing, that is moving in the wrong direction

Different brands are not "automatically incompatible" in fact a lot of brands are just different marketing of the same stuff. But it is impossible to say witch combinations would be bad, oil companies do not list the ingredients of their stuff, even if they did most of us do not have the skills required to determine compatibility

One thing that has been noted with analysis over at BITOG is some oils will give poor results their first few runs, after the surfaces are ‘used to“ the new oil everything settles down mixing is the same but exaggerated

I am not trying to say the engine is going to blow up if you mix oil, in fact it will likely have no user noticeable effect on engine life but oil is cheap, especially dino, do it right, you will feel better about it,