Looking to gain some mpg. Heard the syn lubes in the diffs will add 1-2 mpg. Any truth to that.
What is a good brand?
Do any of the quick lubes carry the syn diff lubes? or is it better to do it yourself?

Also what about syn engine oil?

 

When I went to Royal Purple syn engine oil, I increased 3MPG. I put in RP's differential oil and trany oil and got another 2MPG. They have oil for the PS pump and I expect another 1.5 MPG gain.

Shoot, I woke up.

I do use RP synthetics and do think I get better mileage, but it could be my HO is broke in and I don't drive it as hard as I used to. I was a DELO fan but now use RP Syn. Both are good. If I were to guess (yes, guess), I would say I do not get more than 1 mpg increase with synthetics.

 

I don't see how. The trucks come factory filled with synthetic.

 

I have 9K miles on my truck . . . getting ready to put Amsoil syn 75w/90 in the diffs. They are supposed to have synthetic in them from the factory. However, in several other posts, guys are saying that the factory oil looks thinner than 75w/90. I don't know . . . . haven't changed mine yet. Also, some guys are running 75w/140 in the rear diff.

 

Expect better climbing on the gears from synthetic gear oils when the temps get cold. Synthetic gear oils are also known to make rear ends run a little cooler.

Don't expect a big increase in MPG, just peace of mind from the added protection.

 

I'm a FIRM believer in syns in the boxes. So are the mfgrs - I just think they use low end stuff. I'm still not totally sold on engine syns, even tho I use it. I only use engine syn for the longevity because I haven't seen firm proof that petro oil is definately good for ext. drain programs. I had a hot running Dana 80 and I tried Ams. 2k 75w90 - that was the best they had, then. It not only ran just as hot but it got noisy, too. Then, I tried RP 75w90 and after 3k more miles, it stopped the noise. Then I decided I needed heavier lube for the hard towing I was doing so I switched to RP 75w140 for a few 1000 more miles. Next, I found out how much more the viscosity index jumps with the 85w140 (over the 75w140) and switched again. The 75w140 was doing fine but I will say the RP 85w140 is out of this world! I didn't notice any mpg decrease, even in Co. winter. Now, I have an abused, neglected and abnormally worn AAM (thanks to the first owner) and I use RP 75w140 because I haven't been towing much these days. Again, it's doing good but the next change will be to RP 85w140 for sure. Craig

 

Can I use 85W140 in my diff for light duty use? I don't do heavy duty towing but would like to use the best stuff there is for longevity.

I bought my Ram 27 December 2006 and rear diff covers is totally rusted so, combining the 79k miles on the 2004 and the rusty cover, I suspect overheated and wasted fluid. I'll be adding a PML or MagHytec cover and some updated fluid shortly.

 

Yes, you can. I use 75w-140 and don't tow heavy that often.

MikeyB

 

It wouldn't be necessary. Also, The RP 85w140 was the only lube I didn't have to use FM in the Dana LSD. Ams 2k 75w90 HAD to have it right away - that one was the worst for the chattering on corners. The RP75w90 didn't need it til a few k miles. The RP75w140 needed it after about 7k miles and the RP 85w140 didn't need it at all at 24k when I drained it. I didn't do ananysis on the RP 75w140 because it wasn't in there very long but the RP 85w140 was the ONLY one that would go 24k and was still OK to continue use. All the others I sampled were done at ~12k or had recommendations to sample again soon. Another testimony for the RP85w140. I switched to it at about 45k on the 80 diff and at 48k on the diff, my nephew and I changed the carrier and pinion brgs. We used his oxy/acet torch for a brg heater and we had to pull the brgs a few times to get the shims right. The brgs were already coated with the 85w140 and on the second try with the shimming, we got a little wild with the heat on one of the brgs and started discoloring the race and the lube wasn't burning off yet ! Neither of us would have believed it if we hadn't seen it! I know there's other good products out there but I stick with the ones that prove themselves to ME. Craig

 

so with the royal puple, you have to put a addittive in the rear diff?
What about fr diff and transfer case for RP?

 

I would tell you to go to RP's website, but their website isn't the easiest to navigate around in order to try and find information. I'd give 'em a call and ask 'em about the friction modifier. I'd venture to say that it's not needed, but I'd verify that with RP.

RP doesn't make an ATF+4 equivalent so that's a negative on the x-fer case, but you can put their 75W-90 in the front end.

I'd suggest checking out Red Line fluids. IMO, Red Line makes the best gear and trans fluid available out there

 

my owners manual says in at least three different locations that friciton modifier is NOT required. 2004 11.5" AAM w/ LSD.

 

No need for the linited slip addative in the diff. The truck came stock with syn. I just changed mine and put in Mobile 1 Syn.

 

I am using the Amsoil Severe Gear 75w-140 and have gotten along great with it for 10K miles or so.

I am almost always hooked to a trailer with this truck and wanted the extra film strength.

What I can't believe is the difference in temp between the stock and Valvoline 75w-90 diff fluid and this Amsoil 75w-140. I was pulling a very heavy load at highway speeds last weekend. Stopped for fuel and stuck my hand on the diff and it was just warm. When I used to do that with the 75w-90 (either brand) it would be so hot I could not leave my hand on it for more than a couple of seconds, with much lighter loads. I don't know if it is the viscosity or the brand, but it really is working.