Originally posted by chuck
and is it important? I'm putting synthetic oil in the gearboxes tomorrow. Dodge manual recommends synthetic if there's going to be any significant towing...they recommend 75w-140. The dodge dealer wants 20 bucks per quart for Chyrsler synthetic gear lube; mobil 1 is 7 bucks....but I think the sae grade is 70w-90. is that a problem? what do those numbers mean?
For lack of a better way to explain it the lower number is the viscosity of the oil at a certain low temperature (like 32 degrees) and the higher number is the viscosity number of the oil at a certain higher temperature (like 180 degrees).
If Dodge recommends 75W140 then use 75W140, NOT 70W90. I had problems with the rearend of a Ford Ranger running 75W140 instead of the recommended 70W90.