Engine oil mix... Can it be done?

I might ruffle some feathers here.... But if both are each ok run on an individual basis, I would mix them with no concern.

And here's why I don't think it is an actual issue: if it were, all manufacturers would have strict warnings about only topping off the oil on the pre-ride checklist with the exact oil it was filled with. But they don't. They simply give a broad spec of what the oil needs to meet. Also, if mixing were a problem, they would have to require near complete engine disassembly any time you wanted to change which oil you use after an oil change. But you don't see that warning in any manuals. Heck, even my Honda Rancher 400 states in the service manual that an oil change still leaves 20% of the old oil in it. So if you are filling with a new synthetic for the first time after an oil change, that's way worse than just topping off like the OP wants to do here. And my final reason, is that most manufacturers also give a fill amount for doing an oil change without changing the oil filter. And doing so would leave a lot of different oil to mix. If mixing were a problem, you would see strict warnings in the manuals in this location.

BUT, peace of mind is worth a lot, and ultimately only zero mixing of oils can absolutely 100.00% guarantee that. So I'd completely understand if you tell me I'm just full of smoke.

The linked post was my machine.
I am more sceptical than probably anybody. I still don’t believe that a simple mix of oil’s caused my smoking issue. But I saw it with my own eyes.
With a combustion clean and the swap back to the regular oil the smoking is gone.
I did mix three different types of oil together. I mixed Amsoil 10 W 40 synthetic with Yamalube 10/40 with Canam semi synthetic (mystery grade. I assume 10/40.. they don’t list it)
I am going to say that it wasn’t so much a synthetic mix with nonsynthetic oil problem, but more of a chemical additive mixed with a different chemical additives that cause the undesirable results.
The mechanic I know, in my mind is a mechanical genius. He is retired now and has been a mechanic, a mechanic teacher, he created the mechanic course curriculum with the board, he does mechanical accident recreation, does all the mechanics talk shows on the radio. He has a bit of OCD. And once he gets his mind on a topic, he researches it to death. He will talk your ear off for two hours on the properties of oil versus synthetic oil.
His exact words were. “The chemical properties in one oil allowed sheer heating of the oil fins in the other oil which caused them to burn. The burnt oil fins gummed up the rings on the piston, the sticking rings cause the smoking issue until the engine warmed enough to release the ring. Once the engine was cool the ring with stick in place again. “
He told me he has seen a diesel engine that had the same issue and the rings were so gum to the engine would not run in the truck had to be towed to him. Combustion chamber cleaner did not fix this problem. He said they had to strip the engine down and re-ring the cylinders. The old rings look like black carbon glue rings.



Sent from my iPhone using Tapatalk Pro

I just got back from the dealership and get a load of this....

I ask the guy at the counter if it's ok to mix Yamalube with ATV synthetic wet clutch compatible oil, just to top off, and he answers "No, never never never mix two different types of oil even if they're both the same grade. And never ever mix two different brands of oil either."

So, I tell him, ok then I'll take one bottle of your Yamalube 5w30. Now here's the good part. He tells me that they're all out and gives me another brand and says "you can use this instead". I look at him and say "you're kidding me right?!". Nope, he was serious. His argument: it's been verified and it's the oil that is the most compatible with Yamalube.

I paid for the oil and as I started walking out the door I say to him "Never ever mix two different brands of oil". He turned beet red.

wheelsquad said:

I might ruffle some feathers here.... But if both are each ok run on an individual basis, I would mix them with no concern.

And here's why I don't think it is an actual issue: if it were, all manufacturers would have strict warnings about only topping off the oil on the pre-ride checklist with the exact oil it was filled with. But they don't. They simply give a broad spec of what the oil needs to meet. Also, if mixing were a problem, they would have to require near complete engine disassembly any time you wanted to change which oil you use after an oil change. But you don't see that warning in any manuals. Heck, even my Honda Rancher 400 states in the service manual that an oil change still leaves 20% of the old oil in it. So if you are filling with a new synthetic for the first time after an oil change, that's way worse than just topping off like the OP wants to do here. And my final reason, is that most manufacturers also give a fill amount for doing an oil change without changing the oil filter. And doing so would leave a lot of different oil to mix. If mixing were a problem, you would see strict warnings in the manuals in this location.

BUT, peace of mind is worth a lot, and ultimately only zero mixing of oils can absolutely 100.00% guarantee that. So I'd completely understand if you tell me I'm just full of smoke.

Click to expand...

110% true, if there was a drama with mixing oils the factories would be covering their butts bigtime, but their not, all oils these days are detergent oils but, back in the bad ole days there was no detergent oils, just straight mineral & the bye product of this oil was that it left a "shellac" on ALL internal parts, this "shellac" stuck like glue but sometimes would come off & trash motors, then came detergent mineral oil designed to keep internals clean & it worked like a ripper bit like paint stripper! So good that it ripped the "shellac" of everything & motors blew up everywhere if you didn't do regular oil changes & that's where story started about not mixing oils, I saw this 1st hand, so small top-ups between changes won't be a problem, but if your using different types of oils to top-up your either being a maintenance miser & not changing at the proper intervals OR you have an oil usage problem that needs looking into.

So much of our "knowledge" about automotive maintenance, and many other subjects as well, is historical knowledge which may have changed, or marketing which may not have been true in the first place, or incorrect observations and suppositions by amateurs with wide audiences, with misinformation being spread around just as much as facts.

So how do we tell them apart? We can't, but we try to apply our best common sense and logic and critical thinking. We DON'T just agree to something that any old rando on the internet who claims to have solid, irrefutable information tells us.

We could argue this till the cows come home and it changes nothing.
The arguments have been presented. The OP has made his decision.
The information is all laid out here for future readers to review.

May everyone make good choices for their machine's longevity.