I just swapped out my 3.54 FD w VLSD for a 4.083 FD w VLSD pumpkin.
I'm using Royal Purple 75W-90 gear oil
The differential felt fine when I compared it to the original, not sloppy, not tight if thats worth anything.
Took it for a short drive last night after the install to check for any whine or vibration and nothing whatsoever. Very smooth and quiet.

Drove it on HWY today, about 65 MPH for about 20 miles and noticed my Nismo diff cover was extremely hot to the touch. Basically can't put my hand on it for any length of time. I haven't wailed on the car either.

Googled and found many different opinions on diff running temps...from 100 deg F to shouldn't be able to touch.

This doesn't seem normal, or is it? I know the Nismo diff cover has fins on it to act as a heat soak, but these temps seem somewhat extreme.

 

the nismo diff cover might have fins but its not like a radiator where the surface area is greatly increased, even something small and cheap like our stock power steering cooler will provide more cooling. why the track guys install a diff cooler. as to exact temps........ never really given it much thought

 

My diff always ran well over any temperature i would want to touch. I know when I changed the diff fluid after driving it was well over 100 deg F even after it had cooled down for a while.

 

checked into it a little bit and it seems ~200 degrees is pretty normal and under extended load(in this instance towing a trailer) close to 400(370 in this case) is pretty normal. royal purple tests to 100 degrees C(212 F) and the flash point is 325 degrees F need to get temp to find out for sure since 212 you shouldnt be able to touch period without getting burned.
http://royalpurpleconsumer.com/asset...log_032613.pdf
http://www.lastgreatroadtrip.com/wp-...comparison.pdf

 

Thanks for the posts.

I probably over did it with the hwy driving. Supposed to do 10-20 miles for break in and take it easy for the first 500 miles but I went ahead and did 20 maybe even 25 at hwy speeds. Regardless of how gingerly I may have driven that sucker was still turning pretty good at 65 Mph.

I wish i had payed some attention to the old unit before doing this install.

 

Even a short drive around tow never going over 35 mph will heat the diff up a lot

 

Especially with any sort of locking differential, most use friction to transfer power in different directions. Friction = heat