How Long for Gear Oil To Warm Up?

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2014 RAM Express, 3.6/8speed auto,3.55 gears. It was 22° at 3:30 P.M., the EVIC starts the engine oil temp out at 104°. It takes almost 7 miles until the oil temp gauge starts climbing, 105°, 106°, etc. My question, if the engine oil takes that long to heat up, how long, or does the rear gear oil get up to temp? I've got a thermo gun and shot it as soon as I got to work. It showed 84° on the rear cover. Does the rear gear oil, in this cold, ever get up to normal temp??? Not enough miles? That 84° was after 25 miles @ 55MPH. Your thoughts please.
 
For you situation you can answer all these questions with that thermo gun. Take some notes and let us know. Where I am the temperature last night plummeted clear down to 55F at about 2 in the morning so my numbers will be different from yours.

At least you don't have to worry so much about burning off the moisture with gear oil like you do with engine oil.
 
Yeah you have to run the experiment.

You can also calculate with some basic assumptions, in terms of average power, driveline losses, and heat capacity of the lube (ignoring losses through the case would be a best case scenario, but I'd probably add heat capacity of a notional amount of iron for the case and gears). Should be no more than a five minute calculation.
 
I suspect the gear oil reached its stable temperature after 25 miles.
Just some rough guesses, but maybe your truck needs 30-40hp to maintain 55mph, and the diff is might be 95% efficient at that temp in transmitting hp. So 2-3 hp is being wasted as heat to warm up the diff? So 1500-2500 watts into 100lbs of metal going 55mph in 22F isn't going to get very warm.
I tried regular 80W90 gear oil in the diffs and transfer case of the Tracker one summer and it was fine, but come winter the drag was quite noticeable below freezing and terrible near 0F for 4-5 miles. I had to change it out to some syn 75W90 one a warmish day...
 
NASCAR goes to the extent of blower cooling their racing diffs. What you need is a diff oil cooler with thermostat, in order to compensate for summer heat and winter cold, but that will have to be aftermarket. Without a thermostat you have a "too thick for winter, too thin for summer" juggle to perform.
 
Today truck said it was 41° when I left work. Drove my 25 miles home, got out and took temp at bottom of differential cover, 84°, and up front by pinion yoke, 95°. I know outside temps have a huge part in rear end temps, so I'm assuming the gear oil itself was a little hotter. Interesting to me.
 
Towing anything?

60F over ambient... Its warmed up!

And is why some automakers moved to 75w90 and 75w85 gear oils.
 
No temp readings taken but the diff housing on my e-450 van running at about 13,000 pounds was too hot to touch after a long drive this summer.

Next time I drive it I will check with IR gun to see.
 
High Pressures on the localized surfaces of the gear teeth, due to torque and friction, raises temperatures at those localized surfaces and the gear oil.

This heat is transferred to the bulk (sump) oil by which raises the bulk oil temperature.

It takes a while to raise the temperature of the bulk oil and transfer this heat to the diffy case.

The bulk oil temperature is generally higher than the case temperature by about 20 to 60 F until the system reaches equilibrium.

On a cold day, it takes longer for the oil to reach an equilibrium temperature.
 
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Took 2 ounces of factory fill 75W140, put it in small plastic pill container. Froze it to 8°, would hardly pour to top of container. Man that stuff is thick being that cold and a synthetic from factory.
 
I like this video...note it's showing a grossly mis-matched oil versus a correctly specified oil.
 
Interesting video. I don't know much about oils, but would not have guessed that going from 75 to 80 would have been that drastic.
 
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