Went to grab some Mobil 1 to do my rear differential when my new PML cover arrives tomorrow. The local auto parts store only had 3 quarts of the Mobil 1 75-140 Synthetic on the shelf so I grabbed 2 bottles of Mobil 1 75-90 Synthetic. I didn't have the time to drive another 5 miles to check another store.

Will I have any issues if I mix these 2? Both are full synthetic. I will probably end up with 75-120 once everything is said and done.

BTW, the 75-140 ain't cheap. I paid $16.99 a quart. The 75-90 was only $7.99. If I wasn't getting ready to tow heavy for 600 miles through the Arizona desert, I would have gone with the 75-90.

 

I wouldn't worry about it but I definately wouldn't skimp on the next change to see what it looks like. I run the amsoil and it is 75-90 and haven't had any problems.. I also tow heavy!!! all day every day!

 

I also ran into the same thing with the same oil and I done exactly the same thing you did , I towed a 32 gooseneck load to AZ , no problems.