What is the difference between ';synchromesh'; gear oil and normal 75-90?

I have a 2000 4.0 jeep wrangler and about 3 months ago I put a synthetic 75-90 gear oil in the tranny. I recently found out it was supposed to be a ';synchromesh'; oil. I went to all the local auto stores and none of them carry the oil. In one of the stores a mechanic was in there and he told me all synchromesh is, is a thin motor oil. He said I could use a 0w-40 mobil 1 synthetic oil and it would be just fine. Is this okay to do?What is the difference between ';synchromesh'; gear oil and normal 75-90?
sychromesh is for manual transmission





normal oil is for auto boxes








take your pick!





dont use motor oil in a gearbox, it doesnt have the right mix, such as extreme pressure addititivesWhat is the difference between ';synchromesh'; gear oil and normal 75-90?
There is not such thing as synchromesh oil. Manual transmissions use the oil for which they were designed. It ranges from ATF to ';fish oil'; to light gear oil. 75-90 would be a rear-end dope and probably too heavy for your trans although if it seems to shift well then it may be the right stuff. Generally thinner oils help the shifting and thicker oils hinder the shifting. Get the parts store to look up the correct dope and put that in it. They have a book that tells them. Otherwise, call a dealer or just take it to one and have them change it.

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