Aluminum Differential Cover Thermal Results

[Blacklane]

I recently installed a finned aluminum differential cover from PML Covers on my 2012 Chevrolet Avalanche 1500 that I intend to use for towing a travel trailer. In my previous truck, I had to replace the differential bearings, which is not a small task, so I wanted an easy way to drain and fill the fluid regularly in the hope of avoiding the same problem in my newer truck. So I wanted a good differential cover with drain and fill plugs.

I powder-coated the cover in gloss black to match everything else under my truck. Installation was simple. I replaced the differential fluid with AMSOIL Severe Gear 75W90. I used a paper gasket and used medium loc-tite on the screws. (I once had some diff screws loosen causing a loss of fluid).

I have a thermal camera and I had a chance to take thermal images of the differential before and after installing the PML cover. I took both images after towing a trailer for about an hour on a highway, followed by about fifteen minutes of slower, steady driving. I could not perfectly duplicate the ambient temperature, so one image is at 70F degrees ambient and the other is at 80F degrees. In the thermal images, you can determine the ambient temperature by looking at the frame temperature in the background, which is pink/purple/blue.

I assumed that the stock differential and axle had plenty of heat-dissipating area, since the oil can flow all the way down both axle tubes. A few square inches of aluminum fins would not add much. The thermal images revealed a different story. The stock differential temperature was mostly 170-200 degrees F while the PML differential was mostly 140-150 degrees F. The axle tubes are green colored, indicating that little heat is transferred down the axle tubes.



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Full disclosure: I also sent this info to PML Covers who posted it on their website and sent me a tee shirt, so I guess you could say I have a bias. However, I think these results would be applicable to any similar differential cover.

[mike-s]

Blacklane wrote:

The new aluminum cover is indeed much thicker than the stamped steel stock cover. That gives it more thermal mass and makes it slower to change temperature. Additionally, the aluminum cover is designed to hold 0.5 quarts more fluid, which also adds thermal mass.

The thermal mass makes no difference to the cooling ability. It just means it will take longer to heat up AND longer to cool down.

Blacklane wrote:
painting the surface black improved the thermal performance.

Black does help with radiative cooling. But the vast majority of the cooling here would be through convection - lots of surface area, lots of moving air when going down the road.

[Blacklane]

PDX.Zs wrote:

Blacklane wrote:
r, but I had to replace the 4 differential bearings and 2 rear wheel bearings at around 160,000 miles. All of them had severe pitting.

Wow!

I know that is not the most robust axle in the world, but that is basically unheard of.

My (educated) guess is that there is something more than heat or towing going on here. Perhaps a bent shaft, bent housing (less likely) or a bad install.

Either way, the diff cover looks nice. 🙂

These are some of the bearings from the differential in my old Chevy truck. I don't think excess heat had anything to do with this failure, however I suspect that tiny metal flakes from a single failing bearing slowly destroyed the other bearings. I think that if I had changed the fluid regularly, the problem might not have cascaded into destroying all of the bearings. That's the main reason I replaced the differential cover.

[Blacklane]

mike-s wrote:
That picture doesn't show what is implied. Put a piece of styrofoam or other insulation on the cover, and a picture of the outside will read an even lower temperature even if the internal temperature is unchanged. Aluminum is about a 4 times better thermal conductor than steel, but you also have to consider the thickness. I'll bet that aluminum casting is more than 4 times as thick as the steel original, so probably provides less cooling.

GordonThree is right, 10 degrees lower for both ambient and the same spot on the diff. The cover isn't making a difference.

The new aluminum cover is indeed much thicker than the stamped steel stock cover. That gives it more thermal mass and makes it slower to change temperature. Additionally, the aluminum cover is designed to hold 0.5 quarts more fluid, which also adds thermal mass.

I tried to control for these by taking the measurements after a good, long tow. After about an hour, I figure the temperature is at steady-state. Additionally, the larger thermal mass of the aluminum cover makes it equally slower to cool down, but I tried to keep those the same times as well.

I think it's helpful to look at the big chunk of iron near the axle tube. That should be a good place to compare the two configurations since it's the same for both. For the baseline case, that's showing "white" or around 199F. For the aluminum cover case, it shows "deep red" or 151F. (As a matter of chance, that spot was centered in the image and the exact temperature read-out was there).

[Blacklane]

fj12ryder wrote:
Yeah, painting the cover was a bad idea, why use something to help dissipate heat and then use paint to help insulate it?

Actually, painting the surface black improved the thermal performance.

The layer of paint has negligible insulating properties, however the black coating greatly improves the thermal radiation away from the aluminum. This was proven in 1804 using a Leslie cube filled with hot water. The 4 sides of the cube were painted with different coatings, including copper and aluminum, but the black side radiated the most heat. The experiment is often repeated in grade-school science classes using different materials with similar results.

[fj12ryder]

Yeah, painting the cover was a bad idea, why use something to help dissipate heat and then use paint to help insulate it?

I doubt that adding capacity will help with temperature control. It will all reach the same temps regardless of amount, amount may increase the time it takes to reach max temp, but not by much.

[TNRIVERSIDE]

I replaced the differential cover on my 2009 Ford F-150 with a similar aluminum oversized cover. I replaced the Ford fully synthetic lubricant with another brand of fully synthetic lubricant. My brother-in-law was towing a similar trailer with a similar truck with standard differential cover and synthetic ford lubricant. I had checked both differential covers while I was using my stock for cover and the temperatures were very close. After the installation of the aftermarket aluminum cover I only saw about a 10 to 15° drop in temperature. I know it's not scientific research but it's my findings for what it's worth. The main reason I installed it was ease of changing gear lube.

[Acdii]

I also think that cover adds capacity to the fluid, which will also lower the temps as there is more of it. Ambient temps also have a much larger influence on these tests, and 10* can make a much larger difference than assumed.

In any case, just the fact you replaced the cover and now have easy maintenance, makes it a winner in anybodys book.

[hawkeye-08]

Send pictures to Amsoil showing how their oil lowered the temps and get a free shirt from them too!

Regardless of contributing factors, nice job lowering temps.

[mike-s]

That picture doesn't show what is implied. Put a piece of styrofoam or other insulation on the cover, and a picture of the outside will read an even lower temperature even if the internal temperature is unchanged. Aluminum is about a 4 times better thermal conductor than steel, but you also have to consider the thickness. I'll bet that aluminum casting is more than 4 times as thick as the steel original, so probably provides less cooling.

GordonThree is right, 10 degrees lower for both ambient and the same spot on the diff. The cover isn't making a difference.

[time2roll]

My cover had an O-ring to make the seal. Not sure how much it helps but I still like it on there.

[PDX_Zs]

Totally off topic, but LubeLocker gaskets are the bomb for anyone doing anysort of regular maintenance on diffs.

🙂

[theoldwizard1]

Race cars have been using synthetic gear lube for MANY years. It greatly extends the life of the gears (quick change gears are straight cut and wear pretty quickly with conventional oil).

And yes, the gears run cooler in synthetic lube.

[Cummins12V98]

Next time forget the gasket and use the RiteStuff by Permatex. Also by painting the conniver you decreased the cooling of the aluminum cover.

Good call on the AMZ/OIL SevereGear!!!

[PDX_Zs]

Blacklane wrote:
r, but I had to replace the 4 differential bearings and 2 rear wheel bearings at around 160,000 miles. All of them had severe pitting.

Wow!

I know that is not the most robust axle in the world, but that is basically unheard of.

My (educated) guess is that there is something more than heat or towing going on here. Perhaps a bent shaft, bent housing (less likely) or a bad install.

Either way, the diff cover looks nice. 🙂

[Community Alumni]

GordonThree wrote:
Am I missing something? 10 degree lower ambient, 10 degree lower device under test?

Looks more like about a 50 degree difference. If you look at the white hot areas of the first image and compare those same spots in the second then you can see the difference. Reference the color scale on the side of each image.