Went shoppin for differential fluid and all they had was 6 quarts of Mobil 1 Full Synthetic 75W90 ($9.99/qt) and 3 quarts of Royal Purple Full Synthetic 75W90 ($9.99/qt), so I bought all the Mobil 1 and one of the Royal Purples...is this going to be ok mixing them or should I try and find another quart of Mobil? I have never mixed fluids before and just want to make sure I'll be ok...both are good products from what I hear.

 

I would think you would be OK mixing them, if they are the same weights

 

I don't think it would be a good idea at all. The biggest reason is you do not know how the two types of fluids will react with heat and such. The worst case would be jelling and the best will be no difference at all. You are just gambling on the differential IMO.

 

Hearing this ONE time is enough for me...the only reason that I asked was because I had heard that Royal Purples were "interchangable" with other oils of the same weight...

 

i have heard that also about being compatable with other oils

 

I would put 4 of the Mobil in the rear, and 3 of the RP in the front.

 

They are compatible... no problem....
Although given that choice... Go with RP... Better quality!
I am about to do mine and I will use Schaeffer.

Oilguy

 

Geez...with a name like "oilguy" I don't think I can question that. Reckon I'll take the Mobil back...thanks guys

 

If taking it back look for a 5 gallon can of diff fluid. I bought one and it was about $110 at the time. Changed out two times already and about to do it again but will need to find another can (as in $$$$ to pay for it). The cost comes in about $6 a quart. Valvoline, full synthetic, is what I bought. If the oil is good enough for the engine then the 75w-90 should be good enough for the diffs.