My rear diff fluid was low.. (leaking through the plug onto the cover) I added a valvoline synthetic blend (conventional and synthetic mix) to the oil that was there. I didn't even think about the possible synthetic/conventional oil problem until I had added it. So.. do I need to drain in somehow? Thanks for the help. On a side note, the plug on the rear diff is rubber (on a 93 XJ) Anyone ever seen this before?

 

Was it gear oil, or just motor oil. If it was motor oil drain and replace with gear oil of the proper weight.

 

It's gear oil.

 

If you added synthetic GEAR OIL to the conventional oil already in there it is ok to mix them. I put some Mobil1 synthetic 75w90 in mine, says right on the bottle it's ok to mix them.

 

I would think your fine.

 

great thanks guys

 

I would drain it before it over heats. you have 2 different oils in it that dont work together. viscosity of the 2 oils are different. i bet if you dont drain it it will eventually overheat.

 

You'll be fine. But if you're worried about it, just remove the cover and drain the old mixed stuff out, use RTV to seal the cover and refill.

 

I would think 75w90 is 75w90 no matter the type, why else would they make a blend if they were not compatable?

 

That's what I'm thinking. The oil I added is a conventional/synthetic blend, so I wouldn't think that mixing it with some more conventional would be a problem. But obviously I'm not sure.

 

ya it sounds like your fine....