Is it ok to run heavier gear oil in a stock dana 35? I am running an 80/90wt. will heavier oil make the diff run cooler? I was running mobil 1. 80/90 it looked pretty dark in color when i drained it.
Is it ok to run heavier gear oil in a stock Dana 35?
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It's not all that sensitive to viscosity, you can go to a heavier viscosity but it won't make it run any cooler. By the way it is 100% normal for a differential to run warm/hot enough that you can't hold your hand on it more than a couple seconds at the most.
There is a known way to help the gears to run cooler though, that's simply changing from a synthetic GL-5 gear lube to a conventional GL-5 gear lube. Yes that is true, your gears will actually run cooler when lubricated with a conventional gear lube which sinks the heat out better than a synthetic can. That's why gear and axle companies like Revolution Gear, Yukon Gear, Currie, and Dynatrac specify or require the use of conventional gear lubes to keep their warranties intact or to insure the gears run cool enough during new aftermarket gear break-in process.
Factory gears don't need to be broken in since their manufacturers pre-lap them so they're ready to be driven on when they leave the factory. Synthetic can be used for them. But for aftermarket gears a conventional is required during the break-in since it helps them to run significantly cooler during this critical phase.
So if you want your gears to run cooler, just switch to a good conventional GL-5 gear lube like Valvoline, Mobil, Torco, Castrol, etc. And if your Dana 35 has a Tracloc limited slip differential inside it, make sure the back label of whatever lubricant you buy says something like "Compatible with limited slip differentials" so it will contain the additive required by them.
And for any non-believers, here's one good source of information... John Currie. Contact him and ask why Currie started requiring their axle customers to run only conventional gear lubes. He and and others in the industry were surprised by what they found in the face of an unacceptably high rate of ring & pinion gear failures caused by the use of synthetic gear lubes by their customers.
There is a known way to help the gears to run cooler though, that's simply changing from a synthetic GL-5 gear lube to a conventional GL-5 gear lube. Yes that is true, your gears will actually run cooler when lubricated with a conventional gear lube which sinks the heat out better than a synthetic can. That's why gear and axle companies like Revolution Gear, Yukon Gear, Currie, and Dynatrac specify or require the use of conventional gear lubes to keep their warranties intact or to insure the gears run cool enough during new aftermarket gear break-in process.
Factory gears don't need to be broken in since their manufacturers pre-lap them so they're ready to be driven on when they leave the factory. Synthetic can be used for them. But for aftermarket gears a conventional is required during the break-in since it helps them to run significantly cooler during this critical phase.
So if you want your gears to run cooler, just switch to a good conventional GL-5 gear lube like Valvoline, Mobil, Torco, Castrol, etc. And if your Dana 35 has a Tracloc limited slip differential inside it, make sure the back label of whatever lubricant you buy says something like "Compatible with limited slip differentials" so it will contain the additive required by them.
And for any non-believers, here's one good source of information... John Currie. Contact him and ask why Currie started requiring their axle customers to run only conventional gear lubes. He and and others in the industry were surprised by what they found in the face of an unacceptably high rate of ring & pinion gear failures caused by the use of synthetic gear lubes by their customers.
SPECWAR
TJ Enthusiast
Installed new 3:73 LS center section about 600 miles ago. Broke it in for first 500 miles on full synthetic 80/90, shooting the diff cover every time I drove it with my digital temp gauge. Center section never got over 138 degrees and axles 18” out from center section never got above 87 degrees. Changed over to full synthetic 75/140 at 500 miles, and temperatures all remain within 5-8 degrees now in same locations.
(I’m well aware nobody advises breaking in on full synthetic)
(I’m well aware nobody advises breaking in on full synthetic)
If you understood the issue you'd understand why taking the IR temperature externally doesn't give a useful indication of the temperature of the ring and pinion gears themselves. The diff cover/housing is actually cooler when the differential is filled with a synthetic because it was discovered to not sink/extract the heat out of the gears as well as expected or required for new aftermarket gears.
John Currie mentioned how the IR temperatures they measured externally initially seriously confused them since they were cooler when filled with a synthetic than those filled with a conventional. And it was with axles filled with synthetic gear lubes that had an unexpectedly high failure rate. That was the issue they were working to understand then solve.
It took Currie building a special test jig so they could directly measure the temperature of the R&P gears independently of the lubricant type.
It was then discovered that synthetic gear lubes were acting like a thermal blanket and not extracting the heat out of the gears well enough. That meant the synthetic wasn't getting as hot due to it not readily absorbing heat which is why the housing and diff cover measured cooler than the gears themselves.
The test jig confirmed the gears ran significantly cooler when lubed with a conventional which is far more effective at sinking/extracting the heat out which meant the housing and diff cover will measure a higher temperature. Which simply meant more heat is being extracted.
Yes this issue fooled a lot of industry people but what was finally figured out is why companies like Revolution Gear, Yukon, Currie, and Dynatrac tell their customers to use conventionals in the axles. At least during the all-important break-in. I still run a conventional GL-5 in my axles.
SPECWAR
TJ Enthusiast
Understand your input, and all I had read before and after my install.
Gears and carrier all looked good when break in oil was removed/ replaced. Perhaps I am just one of the lucky ones.
Prior to this install I had always run conventional fluid, but after having total confidence in the person that actually did my install I permitted the use of full synthetic.
My post was not intended to influence anyones choice of lubricants, just state my experience.
Gears and carrier all looked good when break in oil was removed/ replaced. Perhaps I am just one of the lucky ones.
Prior to this install I had always run conventional fluid, but after having total confidence in the person that actually did my install I permitted the use of full synthetic.
My post was not intended to influence anyones choice of lubricants, just state my experience.