torch red

Ok i ordered 75w-90 for my rear end fluid change in my GT

Then i checked in the manuel and it says to use 75w-140......

I called Royal Purple, the tech guy said that 75-140 is primary used in severe heavy duty applications like schools buses and duelies..he even said he knows guy with drag cars using 75w-90 and was very surprised to hear that ford used such a heavy weight in there rears...

So my question is to you who have changed it...can i use the 75w90 or No Way...

Ford_Dude

I haven't changed diff fluid yet but think about it 90 vs 140 and ford says 140
I'd stick with what ford says

vsop

Well, drag cars would not need the higher temp oil. as they run for a matter of seconds, so him telling you drag cars use it does not mean a thing. If he said road racers used it then I would at least think about it.

I tend to stick with ford until a very reliable source can give me better info.. If guys that run mustang road race cars said 140 was overkill I would listen, but I never listen to product reps, If your rear fails he will not replace it for you, and ford might not either from running a lower temp oil

Ford_Dude

its not lower temp but lower viscosity
and although I try to stick with what ford says IF RP made 60W-140 I'd use it
I would worry more about the second number as it is the viscosity and I would only worry about the first number if I was in an arctic climate

torch red

I know there are a few guys on this Forum that have changed it..so i will paitently wait for there advice..thanks so far...i would tend to use what Ford says to use...until like you said i can hear from a reliable source.

I think they RP makes a 85w-140

Ford_Dude

remember the w number is the winter test number lower can be better
although in a diff the gear oil has such a high winter number anyway 75W that might not have much effect on it

schapman

why dont you just buy the royal purple gear oil in 75w140?

Ford_Dude

ya sounds like the thing to do use the right oil RP 75W-140

torch red

ok called RP back..going to return the 75w-90 to Americam Muscle and get the 75w-140 from somewhere else..just have to find a dealer that sells the 75w-140, but at least now I know they make it..

vsop

As the guys at american muscle, they are a really great group of guys. They probably could get it for you.
I moderate a forum for them, for a computer modding supply company they also own. They have great customer service