As already said, for an NV-4500HD you need a GL-4 rated tranny fluid. The only 2 options here are Castrol Syntorque or AMSOIL MTG. I would go with the AMSOIL as its half the price or less, and just as good. (think its around $11 or $12 a litre)[/QUOTE]

gl-4 thats any 80 90w gear oil not synthetic you can get synthetic but penzoil and almost all the manufactures make gl4

 

dodge states synthetic only for the trans.

 

the Chevy dealer is cheaper than the dodge dealer

 

I wouldn't put anything but Castrol Syntorq in it. That MTL was specifically developed for the NV4500 because it has serious heat issues running behind the Cummins. Mopar and GM who both use variants of this gearbox in HD applications both have specific part numbers for this fluid for this reason. I'm sure the Amsoil stuff is a great oil, but I wouldn't trust it.

 

I was told the same thing about the fluid in my 5spd accord only use dealer oil, the same thing a friend was told on his 5600, and they both have amsoil and both shift as good if not better than before it was changed. I will be servicing my trans in the 99 prob next week. I will let you know how it works.

 

that is true, castrol specifically developed that fluid for the nv4500. however the amsoil was specifically made to replace that castrol. I have ran both, I honestly can't tell a difference, but the ams is a lot cheaper for me.

 

Do you tow alot? Only problem is you won't know how it works until after a year or 2 down the road and you end up with either a good, smooth-shifting tranny or a rebuild/replacement for the one that ate up the syncros and bearings.

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Source? Amsoil makes all types of lubricants that cross lines all over the automotive world. Just because they tell you it fits an application doesn't make it entirely true. They did not pay Castrol for the R&D and testing to make Syntorq work for the NV4500, Mopar and GM did.

 

You initially said in your post above that you can use 5W30 motor oil in a NV-4500HD.

This transmission is very picky on fluid and using the incorrect fluid will quickly damage the carbon fiber synchros. Thats why the only real options are The Castrol and Amsoil.

 

regional amsoil rep, will try to find documentation.

 

I have just order mine from amsoil looking forward to it. Whats the best way to fill the tranny up?