Which RP Oils?

[Walker]

Tell me what you think. I'm putting Royal Purple in my front and rear diffs. , T-case, and 5spd. transmission.



1. Front diff. 75w-90



2. Rear diff. 75w-140, or 85w-140. Which one should I use? (moderate heavy tower in Texas).



3. Manual transmission 5spd. NV4500. I've heard the 75w-90 is ok on the synchros. True? Or should I go with the Syntorq?



4. T-case. The DC manual says to use a Dex III ATF. The RP site says that their Synchromax (manual gear fluid) is good for "4x4 T-cases", but their MAX ATF is suitable for Dex III apps. So, which do I use here?



Thanks

 

[JBHale]

I'm running

85w140 in rear diff - no problems

75w90 in nv 4500 - no problems with wear ,been in for 56,000 miles.

75w90 will work good in the frnt diff.

I don't know on the t case , mine isn't 4wd.

 

[lpearson]

I've got Rp throughout my truck, except I've got an auto.



In the Transfer case I used the ATF RP. No problems.

Rear Diff 75-140 Rp

front 75-90 Rp

Engine Oil 15-40 Rp



Also used the RP Power steering synthetic, seems to like it.



Lowell

 

[Texas Diesel]

Use Synchromax in the transfercase.



If you have a MagHytec cover I'd use 75W-90 in the rear as well, never seen over 220F even pulling 12k @ 109F ambient.



You'll love the MaxGear in your 4500, give it 10k miles and you'll be very pleased, I noticed a difference in my 4500 after 10k miles.



Have you considered a PTO filter and FastCooler for your 4500?



Dont forget the PS system as noted above.

 

[Walker]

Thanks Tejas. I've got the PTO filter ready to put on during the change. I just bought a Mag Hytech for the rear too. What's the big differences in the 75w-90 and the 75w-140? I've heard the thinner 90 is so "slick" that the gears could slip if there is any wear on them and the thicker oil (140) is for heavier towing, but shouldn't cause any running "empty" problems. Is it just a temperature thing (both ambient and internal); or is something else that makes you suggest the 90wt?



Also, what's the Synchromax exactly? An ATF hybrid or something, or just a gear oil (if so, what wt)? And it is Dex III compatable I'm assuming, right?



Thanks

 

[Texas Diesel]

Synchromax: http://royalpurple.com/prodsa/scmax.html I prefer the way the Synchromax will help your NV-241 shift into 4wd, either will work, synchromax is what I run in mine. It is a 20W gear oil that is safe for yellow metals (synchronizers)



Put the PTO filter on the passenger side in case you dont know already.



I run 75W-90 in my rear axle with the MagHytec, IMO, 75W-140 is not needed in the rear axle if you have a MagHytec, temps stay low enough in the summer and the thinner oil yields slightly better MPG. It's just a personal choice thing. DC suggests the 140W oil because of the limited capacity and heat rejection of the OEM diff cover. You're right, it's a temp thing. I've never heard of any problems like you mentioned

 

[Walker]

Thanks for the reply TD.



But my DC manual actually says to use a 75w-90 if heavy towing. Oh well, guess I can't go wrong with either. Cost is the same.



Synchromax sounds good to me too.



Thanks again.