Rear Differential Lubricant's Temp Range


The Grumpy Grease Monkey mechanical engineer.
Staff member
I got asked what the ideal rear differential lubricants differential temps should be?
Changing the lubricant's and additives in the differential if its of unknown age or it looks overly black may help durability, and perhaps order a magnet to place on the outside surface of the rear differential too trap and hold metallic debris,
that naturally comes off the gear wear surfaces to help reduce the wear,
will be helpful, but it certainly helps to check your rear differential coolant temps and occasionally verify fluid levels in your differential, after about 30 minutes of drive time

Mark Williams recommends Torco RGO 85W140.
Another good choice is Schaeffer’s Extreme Performance 75W140 part number 170.
as a lube in the read differential,

that fine metallic crap floating around suspended in that differential gear oil could cause thats very easily reduced.



if your towing temps generally run about 20F higher than general cruising due to the increased load on the contact surfaces and bearings
the general temp range most cars see is in the 175F-200F range, higher gear ratios, like 3.73:1-4.56:1 tend to run about 15 F degrees higher than the more common 2.87:1-3.36:1 rear gear ratios
differential lubricant temps above about 175F over time tend to degrade the bearing surfaces and increase wear on the ring and pinion gear teeth surfaces, and much to most people surprise, lubricants based on petroleum rather than newer synthetics are just as effective at lubricating surfaces , but something most people tend to ignore is the fact differential lubricants should be drained and replaced with new lubricant at about every 75K miles from what I've read in several places over the years.
adding a differential cooler is a good idea if you are going to be driving at high speeds and under higher loads such as during road racing or towing a trailer .
now obviously that is also something effected by vehicle weight and the cruising speeds, generally Id consider the differential temps be measured after about 30 minutes of street driving which might include some highway cruising in the 55 mph-70 mph range.
42545.jpg Extech Products


Wide temperature range from -58 to 1832°F (-50 to 1000°C)
any time that your dealing with a potential temperature issue or a trouble issue where , knowing the exact temperature vs what a gauge might say, it helps to have a handy and accurate infrared temp gun handy to locate and confirm heat, levels.

rear differential coolant temps can be significantly reduced with a differential cooler, that has an external lubricant pump and hear exchanger, much like an oil cooler, but those aftermarket rear differential covers with the fins don,t do much more than slow the rate at which rear differential lube reaches the peak operational temps.





related info
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Staff member
This seems pertinent to my situation when I'm towing the 18 foot enclosed trailer with my
(1800 lbs)TBucket inside with my 2008 Lincoln Navigator. I have already changed the the
rear diff fluid at 96,000 miles (7800 miles ago now) with Ford Fluid XY-75W140-QL SAE
75W-140 Synthetic Rear Axle Lubricant.


Guess I will be using my IR gun next spring to see where the rear diff temps are running when I have the TBucket in the trailer and ambient temps are in the 90°s F.
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The Grumpy Grease Monkey mechanical engineer.
Staff member
the used differential fluid looks good for that many miles and the magnetic crap on the magnets is typical for that mileage

btw.. love the clear pictures