This is very interesting to me and I didn’t want to derail the thread that inspired me so here’s a new one.

Maybe this will never take off but at least I’m giving it a try.

I will be driving my 07 E350 V10 about 50 highway miles today (completely unloaded- practically empty actually) and I plan to check the temp with my el cheapo Harbor Freight laser temp gun. I’ll report back here of course.

 

Welp
forgot to do it on the way there.

And then on the way home I checked it. (Fyi I was towing my trailer about 5,000lbs at 65-70mph). It showed 160-180 degrees at the highest reading I could get. That’s checking

Then i dicked around wiith the trailer lighting for 10minutes and checked again and it showed ambient temps of 65-70. Thats impossible right? 10minutes dropping 100 degrees.

 

There's a lot of surface area on the entire axle housing, and it'll dissipate heat very quickly. Best place to get a temp reading would probably be the diff cover.

Interesting topic though

 

I agree that the best place to shoot the temps with an IR gun would be the lower half of the thin sheetmetal cover.
Art is correct, there is a lot of surface area to bleed off the heat to the ambient air, but 100* over 10 minutes does seem like a big drop but I haven't checked how quickly mine cools off just sitting. I do know that even a very light rain will drastically drop the rear diff temp while running on the highway, and it drops quickly as soon as the road is wet enough to develop a fine spray from the tires. I have seen the temp drop from 190's down to 120's with nothing more than a light rain.
I do have a temp sensor in my rear diff leading to an Engine Oil Temp gauge.

 

Yeah, very interesting topic. I'm tempted to break out my college thermodynamics text books (which haven't been cracked in 20 years) and figure out a rough estimate.

Oil's specific heat is roughly half that of water, though. And with all that highly conductive steel soaking up the heat from the gear oil, it may very well be possible.

When you shot it with the IR gun, where exactly were you aiming when you got 190'?

 

Yeah, if you were decellerating for a bit and then suddenly checked the temp, I bet the front pinion bearing would be HOT HOT HOT. (I have a slight grudge with Ford - I've seen a variety of their corporate axles that had an NTN or some other crappy brand of pinion bearing in the front, while the rest were all Timken. That front pinion bearing always looked overheated even with only 30-40K miles on them. 8.8's, especially).

 

We3zs,
what is this set up you have? Can you share a pic or two?

I realized my temp gun had low battery during/after the experiment. Digital battery gauge was flashing. Maybe due to the low battery it was just indicating ambient temp instead of reading the laser point which was 4-5’ away.

I checked the rear rear pan and the passenger side a few places each to get my readings.
Then dicked with the van lights/battery and then checked the driver side of the diff. This is when I got the lower temps. Due to the lower reading I then also checked the rear cover again.

 

Sorry, no pictures of my setup available, but it's a simple installation.
I use a GlowShift Engine Oil Temp gauge https://www.glowshiftdirect.com/blac...erature-gauge/ and replaced the rear diff oil fill plug with a brass plug. I then drilled and tapped the brass plug to take the temp sensor and then extended the wires up to the dash mounted gauge.
Its not perfect as the sensor isn't submerged in the oil, but once moving the oil is in constant flung contact with it. I did loose the benefit of the magnet in the stock plug but I am OK with that and my shorter cycle lube oil changes. I do the diff oil at 30K miles along with a trans flush for my dedicated tow rig EX, I use a reusable Lube Locker gasket on the '08+ finned aluminum cover which makes the changes quick and easy.

 

Starting at post 1830-50 we had a similar discussion; wet probe vs. surface probe. I've never seen higher than 150 F on a 105 degree day in traffic.

https://www.ford-trucks.com/forums/8...-truck-46.html

 

I used the same laser temp gun today and it was on Celsius.

It has me wondering if if I missed that during my story above.