Synth gear oil for F250 superduty; RP or RL?

[kincade]

I've been searching and reading here for the last 2 hours, and I can't seem to figure out the answer to this question. I'm changing my oil in my diffs in my 2000 F250 superduty powerstroke; and the only synthetic lubes I can find locally are Redline, Mobil 1, and Royal Purple.

I've read that the Mobil 1 isn't so hot...

Redline and RP both look to be good oils. But the viscosity of the RP seems to be quite a bit thicker; and their marketing is a bit, uuumm, full of made up terms.

Conversely, I've read a few posts here about the Redline breaking down very quickly.

So; what would you recommend for this application. I tow around 6k# in the summer, anywhere from 70-100* ambient, and wintertime is usually anywhre from 20-low 30 degrees.

Thanks for any advice you can give!

 

[ConfederateTyrant]

Redline 75w-140 for local purchase or Amsoil Severe Gear 75w-140 if you do not mind ordering online from one of the Amsoil site sponsors.

 

[unDummy]

As long as the change interval is reasonable, any of the gear oil brands you mentioned will work.

 

[jmac]

I use RP in my SD rear, it does the job well and need no FM added for the LS. Mobil 1 will require the FM added. No experience with RL but it is supposed to be very good. I would trust the Amsoil sever Gear as well. need to find out if it needs the FM.

 

[JustinH]

I used the royal purple, because it didn't require friction modifier to be added to the diff.

Not a problem at all, I would recommend using that gear oil.

 

[1sttruck]

I've been using M1 75w90 or 75w140 in a 3/4 ton diesel, no towing, and find that it works fine. At the 15k and 30k change intervals it looks like a darker olive oil, no metal flakes that I can see. The 11.5in AAM doesn't need an additive, and has a weird change interval; either 15k or apparently none.

 

[bruce381]

RL 75/140 gears like thick forget the 80/90 stuff to thin
bruce

 

[kincade]

Thanks for all the advice. Sounds like they'll all work just fine. I ordered some Redline from Summitracing this morning, hopefully that'll work fine for me!