Rear differential warming

[oil pan 4]

In my quest to build the ultimate corporate GM 10.5 inch 14 bolt full float rear axle I want to include a provision to at least warm the oil.
I am going to add a cast aluminum diff cover as one of the many mods, mainly:
because they have fill and drain plugs on them so you can do oil changes with out pulling the diff cover.
can drill and tap additional holes to install equipment
to have the additional holes I add not leak expensive mobil1 gear oil.
to look cool.

I am going to use a Kat's 400 watt, 3/4'' pipe thread tractor engine block heater. 3/4''NPT is the smallest you can get and I know I can make a hole for this and attach it since you only need a drill a 3/4 inch pipe thread tap for 3/4 (applicable part numbers for this engine block heater: GE360, S07090 and 11409)

I need to test this little guy before I install it, 400w over that small of a surface area may get too hot and scorch the oil, so if that happens I will have to devise a way to reduce the voltage to the heater, since this thing is intended to heat coolant, not oil.
I am not going with those stick on heater pads because they suck, but they are better than nothing.
These kat's heaters are pretty neat, they look like you could adapt and install them to heat almost anything.

The GM 14 bolt weights around 550lb, about as much as a V8 engine. But unlike an engine block it only has a few quarts of fluid to warm, so I am going to include a temperature switch. A Reznor Fenwal thermo switch that opens at 150'F to turn off the block heater. (p/n: 08-819133-008)

I have put my IR scanner on differentials after a drive on hot summers day and seen read the cover of a 7.5 and 8.5 GM 10 bolt read at little over 140'F. So turning it off at 150'F on a cold day isn't unreasonable, as soon as the oil get splashed around inside the housing it will cool some.

Additional equipment:
I have pondered adding some kind of external pump and oil filter setup, with possible coolant oil heat exchanger. I have never heard of any one burning one of these up so not going to worry about adding any kind of active cooling. Passive cooling and just the added surface area of the lines and filter setup is likely way more than enough for it to stay with in a safe operating temperature.
Adding a filter would be cool because I would pretty much never need to change the gear oil.
Or I may build the pump filter set up as some kind of stand alone gear oil servicing unit. It stays separate from the vehicle. It would be used by raising up the vehicle, connect the pump and filter to the diff housing using preinstalled fittings, turn on the oil servicer and start the vehicle and put in gear and let it run for a little while to circulate oil and the oil get clean (mobil1 can be up to $17 a quart last time I checked and the 14 bolt uses 2 to 3 quarts of oil).
But there are a few things I don't know.
I don't know what the max temperature on the 14 bolt or any other differential gets when its cold out, I only checked with my IR gun during summer.
I don't know how much heat the 14 bolt puts off. They may never get past being slightly warm or only slightly cool to the touch in winter. Which means that oil is only going to get about as thin as honey.

[aerohead]

There's a research paper available online which shows max equilibrium temps for all auto fluids at different ambient temps.
If you do a search for temperature effects on lubricants it might take you directly to it.

[oil pan 4]

After driving 6 or 7 miles the rear warmed up 15'F to 100'F.

[WE3ZS]

I have a little bit of data that may help some.
Not a GM 10.5 but on a Ford/Sterling 10.5 under an Excursion (Super Duty platform) outfitted with 4.88 gears. My EX is our tow rig, we pull a '14 Jayco Eagle 338RETS travel trailer that is 41' long and weighs 11,000lbs for a truck/trailer combined weight of 19,000lbs. I monitor the diff oil (Mobil 1 LS75W-140 synth) with a GlowShift Engine Oil Temp stand alone combination digital/analog gauge with the temp sensor located in the fill port plug. We tow about 5,000 to 6,000 miles a year, all East of the Mississippi (so far) mostly in the warm/hot weather. Normal operating temps with this setup are from 150F to a high of 235F, the high was in 90F ambient pulling a 6%-ish grade for 2 or 3 miles at 65 to 55 MPH. After higher peaks like that it cools back down pretty quickly at highway speeds and even a light rain will drop the oil temp 20 to 40F. The only upgrade to aid in cooling was to swap on a stock '08+ Super Duty finned aluminum cover, nothing fancy and no additional capacity, just replaced the '05 original rusty sheet metal factory one. From what I could find back when setting the gauge up this gear lube is supposed to be completely stable up to something like 350F with a flash temp of 404F (207C). With my current setup and usage it gets just hot enough to cook off any moisture that may make it's way into the oil and the lube stays well below any problematic temps. I don't think you will have to have any type of external active or passive cooling setup, maybe just a finned alloy cover.

[oil pan 4]

That is pretty cool I have never seen nor herd of any one putting any kind of temperature instrument in a rear diff before.
I will forget about adding any kind of active cooling then.

For passive cooling I picked up a Nitrogear finned aluminum cover.
Mainly because it has fill and drain ports. Also has a little more room for fluid over factory stamped sheet metal. It looks nice and as a bonus its made of thick meaty cast aluminum so I can add additional threaded ports if I wish.
If I get really worried about it I will paint the shinny aluminum flat black.

[me and my metro]

Big trucks hauling logs and dump trucks have temp gauges on their trannys and both diffs. FYI

[spacemanspif]

Friend of mine has a Subaru STI that has a rear differential temperature sensor. NASCAR and other race cars run external differential coolers, I believe. Does using the full plug hole for a temp sender give accurate results? I thought the probe needed to be submerged for accurate readings, WE3ZS might see quick cooling if the sensor was submerged during the climb, and in the air while on the flat/down slope. My experience with rears is to fill until the oil flows out of the hole, if Fords are filled differently, my statement might not have any relevance but if I were adding a temp sender to anything, I'd make sure it was in constant contact with the substance it is supposed to measure.

[WE3ZS]

Originally Posted by spacemanspif

Friend of mine has a Subaru STI that has a rear differential temperature sensor. NASCAR and other race cars run external differential coolers, I believe. Does using the full plug hole for a temp sender give accurate results? I thought the probe needed to be submerged for accurate readings, WE3ZS might see quick cooling if the sensor was submerged during the climb, and in the air while on the flat/down slope. My experience with rears is to fill until the oil flows out of the hole, if Fords are filled differently, my statement might not have any relevance but if I were adding a temp sender to anything, I'd make sure it was in constant contact with the substance it is supposed to measure.

Absolutely the sensor is at/above fluid level being in the fill port. And it would be better to have it submerged at all times, but....... My housing doesn't have a provision for a sensor below the level and once moving at highway speeds the fluid is pretty "active" in there. My setup most certainly isn't optimum, but it's the best setup I've seen on the truck forums without either adding holes to my housing (I'm chicken ) or adding a $300 Mag-Hytek diff cover with a drain port I could use (I'm frugal ).

[oil pan 4]

Here is a flir image of my diff after a short little highway trip. The hottest part of the diff cover was 120'F about 5 minutes after I parked it, then in the 3 or 4 minutes it took to find the flir SD card the rear had cooled an additional 6 degrees F.
Looks like all the heat is concentrated around the ring, pinion and diff, you can even see where the level of the fluid is.
In the past the hottest reading I could get with a simple inferred scanner on a diff was about 145'F after I had parked the vehicle.


The nitrogear diff cover was $180 shipped (not installed when this thermography was taken).