Aluminum Differential Cover Thermal Results

mike-s wrote:

Blacklane wrote:
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."

I'm not buying - that's confirmation bias. Explain why the area where the axle tubes enter the diff (which has the most thermal mass) is essentially the same. Comparing the pictures, by far the biggest difference is the cover itself. And, if you think a cover is lowering the temperature by 48 degrees, want to buy a bridge?

I figure that the differential is a big ball mostly filled with oil. The oil is heated by the friction of the gears and that heated oil uniformly heats everything it touches. (I used to think that oil flowed out to the axles where the heat could be dissipated, but the thermal images showed that to not be the case, so all of the heat must be dissipated in the differential housing, or "pumpkin" as it is often called.)

In the baseline "stock" case, the thermal image of the pumpkin is dark red and white, and using the scale on the left side of the image, must be around 160-199 degrees F.

When we change the diff cover and fluid and re-run the test, the thermal image is medium red to yellow, and again using the scale on the left side of that image, must be around 100-150F.

As you point out, the aluminum cover has a very different thermal profile: it conducts differently, it has different thermal mass, etc. So let's look for something that has not changed between the two cases. It turns out that we can see the iron part of the differential under the axle tube. This part has not been changed between the two measurements, so must reflect the heat of the oil in both cases.

Of course, there is the additional adjustment for ambient temperature of -10 degrees F for the second case.

I tried to keep the other variables constant, so we can only assume that there is a reduction in temperature of about 40 degrees F (50F minus the 10F ambient change) between the stock set-up and the new set-up with an aluminum diff cover and synthetic oil.