Gear Oil ?? For Chevy 3500..

[HiccaBurp]

I'm almost at 100k on my '03 Chevy Express 3500. The gear oil in it is 80w-90. I want to change to full synthetic. The syns are 75w-90 or 75w-140. My local store has Royal Purple in both weights, Castrol Full Syn in 75w-140 and Lucas full syn in 75w-90.

Its a cargo van that gets used like one. It's mostly lighter loads, but occasionally its filled to the hilt with materials or towing some heavier loads. I also drive it pretty fast regularly, 80-90mph(if you lived in Chicago, you'd understand!).

My questions are..

1. What is the best full synthetic gear oil?

2. What weight should I use? I'm thinking the 75w-140 wt might be better?

I don't mind ordering online, plus I do have 3 other auto parts stores. I've heard good stuff about RP, but I do use M1 in the engine and I think one of the other stores carries M1 gear oil.

 

[Pablo]

Your other (and best IMHO) choice is 75W-110.

Amsoil 75W-110 Product Code SVT

 

[Jim Allen]

1) "Best" is subject to lots of pedantic debating. You won't go wrong with Pablo's Amsoil recommendation. I've used RP with good results. There are lots of other good ones. Amsoil is higher up the quality food chain than most but I think the correct viscosity is more important than the name brand.

2) I would use a full syn 75W140 in your application because I know from testing that as the load or speeds go up, so does diff temp. It can easily exceed the 212F viscosity rating under a combo of those elements. Basically, for the best protection, you don't want to run below a 90 grade at whatever is the axle sustained maximum temp. Like all other oils, a 90 grade oil's viscosity is rated at 212F. If the oil temp exceeds that, it gets thinner. If you are running at 250F, a very realistic number for a loaded van running at 80 mph, the oil might be into the 85 grade area at that point. A 140 grade might be running at about 110 grade at 250, so the diff is well protected. It isn't immediately harmful to run a little thinner but it can have long term effects for a hard-worked van. It really depends on what the diff temps are. I have run gear oil temp tests on a small number of axles, so my database is fairly small, but it correlates well to axles with similar gear ratios and ring gear diameters. A 3500 van probably has either an AAM 9.5 or an AAM 10.50 rear axle (9.5 or 10.5 inch ring gears), and that's within the realm where I am most familiar. I recommend a 75W140.

 

[HiccaBurp]

Thanks Jim!! My research and knowledge led me to believe the 75w-140 is the way to go. Now the hard part.. which brand??!! LOL

Royal Purple
Amsoil
Redline
Lucas Oil
Mobile 1
Etc...

 

[unDummy]

There is no best.
Since you have RoyalPurp and Castrol at your local store, its a coin toss.

 

[Jason2007]

Id go with Royal Purple

 

[Ben99GT]

You won't go wrong with Schaeffer, Amsoil or Red Line. Out of that list the only one I wouldn't run would be Lucas.

 

[HiccaBurp]

Ben, I see you left out Royal Purple.. any particular reason? I've never heard of Schaeffer, but wow, I read their history, very impressive.

 

[Ben99GT]

I've used RP gear lube, no issues to report. I just tend to think of Red Line's GL-5+ (and the Shockproofs), Amsoil Severe Gear and Schaeffer's Moly Synthetic as the "creme of the crop" though.

 

[HiccaBurp]

Okay, I called around the parts stores and found RP to be $18-20 a bottle. I need 4. Mobile 1 was not any cheaper.. maybe a buck or two. I did find M1 in 75w-140 at Lee Auto Parts for $12.49.. so I went with it. Seemed like a good price. I did find Redline Shockproof for the same price not to far from my home. Is it that much better then M1? I read it's very thick and actually made some cars loose a couple HP on the dyno it was soo thick? I'm sure anything will be better then the 100k on the factory fill!! 8-0

Any thoughts?

 

[salesrep]

The dirt track guys run the Redline shockproof all the time w/o losing any HP. That said I think the M1 or Rp is a better choice for your ap.

 

[Rob_Roy]

Originally Posted By: HiccaBurp
I'm sure anything will be better then the 100k on the factory fill!!


I agree. The Mobil 75w140 will work well and provide some additional protection for your high-speed towing.

 

[Ben99GT]

Originally Posted By: HiccaBurp
I did find Redline Shockproof for the same price not to far from my home. Is it that much better then M1?


It's different, more of a racing fluid designed to help prevent wear against shock loading. But according to Red Line's Australia site Shockproof is suitable for extended intervals.

Quote:
I read it's very thick and actually made some cars loose a couple HP on the dyno it was soo thick?


Nah, Shockproof has a very low friction coefficient. It's a racing fluid after all. The Heavy Shockproof robs less power than a synthetic 75W-90 even though it acts like a 75W-250 in some respects. When I rebuild the Mustang rear and get some 4.88s in there it will be getting Lightweight Shockproof.

The M1 75W-140 will do fine for you.

 

[meangreen01]

I'm using RP gear oil currently(syncromax) and am very happy with it.

 

[HiccaBurp]

Thanks for all the responses. I'm hoping to change it out in the next few days. I also need to change out a leaking axle seal.

Would you recommend doing a UOA? It's the factory fill on a van with 95k miles on it?

Also, can I find a diff cover that is larger for more holding capacity? Where can I find one?

 

[Jim Allen]

From a purely practical standpoint, I wouldn't do a UOA. From an inquisitive, pedantic view, sure. Would be interesting to see how the oil held up but unless you are noticing symptoms, it's probably a waste of your money.

That would be Mag-Hytec Here's where you can see the results of such a cover:
DIff Temps/Tow Axle

 

[dailydriver]

Originally Posted By: Ben99GT
The Heavy Shockproof robs less power than a synthetic 75W-90 even though it acts like a 75W-250 in some respects.


True, but, according to Dave it WILL have a tendency to 'gel up' at low ambient temps MUCH quicker and MUCH more so than their regular 75W-140.

He said this was due to the extra cushioning add pack which lets it act like said 250 weight in this respect.

This is the reason I will not try it until the late spring, and went with the 75W-140 for now.