Synthetic and Fossil Oil mixed in Rear End ??

[cinci5]

Is it safe to mix both, I was going to but the ace ( I say that loosely) at Advanced Auto said no I can't. I always though you could mix them if needed they sell a blend of motor oil ( syn & fossil ) ????????

 

[Craigi]

According to what I have read, and my discussions with the people at Castrol, both "fossil" and synthetic oils are "fossil". It is the way it is processed that makes it what it is.

You are right about blends, and it is okay to mix synthetic and "fossil" lubricants in engines, transmissions, differentials (don't forget the posi-lube in the differential, if applicable). Try to keep the same viscosity oils in the mix or you will change the viscosity to something in between - sometimes desireable, tho.

Hey - - looks like you chromed your aluminum wheels, too. Love mine. Love yours, too !!!

Have fun!!

 

[pws69]

Why would you do this?

 

[davec0_17]

I would not even consider it. Why not just put either the dino oil or the synthic in it? Why take the risk?

 

[Craigi]

Just for the record, I didn't condone mixing, I just passed on what I heard from the so-called experts. I wouldn't mix except if I was without choice for some reason (ie. low on oil and without access to similar) - and even then wouldn't lose much sleep over it. Most of these engines and parts aren't that complicated or magic. They just need good, clean lube on a continuous basis.

 

[cinci5]

Its not a matter of why but if I had to. I replaced trunnions and pulled out yoke and forgot oil would come out!! Now I don't know if original owner put in either fossil or synthetic and without a drain plug it would be easier to just put oil back in than to rip apart entire rear end because of flushing out and replaceing without taking a chance of mixing.

 

[daveintexas]

Well, I own an 18 wheeler, which came from the factory with synthetic gear oil in the transmission and the rear ends. It is a HUGE mistake to mix it with regular gear oil, as it will just gum up.I dont know why your synthetic oil would be any different.Thats just my knowledge of it, however, I know that I would NEVER mix them.

 

[Vettehead Mikey]

It is a HUGE mistake to mix it with regular gear oil, as it will just gum up.I dont know why your synthetic oil would be any different.Thats just my knowledge of it, however, I know that I would NEVER mix them.

Here's what one manufacturer has to say on the subject:

"Can different synthetic motor oils be mixed together?

Mobil 1 is fully compatible with conventional motor oils, semi-synthetic motor oils and other synthetic motor oils, should it be necessary to mix them. However, it is important to note that the superior performance of Mobil 1 will be reduced by diluting it in any way. "

Better call them quick to let them know.

 

[daveintexas]

well, I know you can mix syn. motor oil with reg. motor oil.The discussion was about gear oil, which is not the same stuff.Do what you want, it was just throwing in what I know about syn gear oil.

 

[aapple]

Its not a matter of why but if I had to. I replaced trunnions and pulled out yoke and forgot oil would come out!!...

If you managed to pull one of the side yokes out of the diff while changing u-joints(trunions), you should be asking how that happened!!

The yokes are held in with snap-rings on the inside of the diff. Unless I missed something here...

 

[cinci5]

If you managed to pull one of the side yokes out of the diff while changing u-joints(trunions), you should be asking how that happened!!

The yokes are held in with snap-rings on the inside of the diff. Unless I missed something here...

I never said side yoke's I pulled out drive shaft yoke!!

 

[aapple]

I never said side yoke's I pulled out drive shaft yoke!!

:duh my bad!!

 

[mvftw]

You can definitely mix engines oils. Why, because that is what 'Blend' is. 80% dino, 20% sythectic...

 

[pgtr]

mvftw is correct - They can absolutely be mixed, say in topping up for example. But on the other hand I don't think anyone here would recommend a 'partial' lubricant change - change it completely to remove the old stuff.

The 'gumming up' anecdote? Now that's an old one dating back to the earliest chapters of the great and neverending oil debate wars (remember straight weight vs multi-weight?).

 

[G Winter]

This brings up an intresting point. Many of us have changed the oil in our 6 speeds and rearends from regular to synthetic. It has been done for yrs. Has anyone had any problem with gumming up the oil in the rearend ? I know for a fact that there would be some old oil left in the bearings and gears of a rearend even if you drain it. I have often added regular oil to synthetic in my older pickup when synthetic wasn't available.

Glenn

 

[cinci5]

Just for the record I went wih Lucas rear end lube and a tube of GM
posi-fluid. We will see what happens.