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How hot should a diff get?

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Old May 7, 2007 | 04:48 PM
  #1  
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From: Dinwiddie, Virginia
How hot should a diff get?

I was under the truck today looking at something and bumbed into the rear diff. It was surprisingly hot. I have never noticed this before. I could touch the diff and not get burned but could not hold on to it for even one second. The most heat was located in the front at the pinion bearing and cooled off as you backed away from it. The bottom where the fluid it pooled I could hold for "1 Miss. 2 Miss" then had to let go.

I have had zero problems, noise or complaints from the rear for the past 200,000 miles. In fact I brag about it. Did me braging catch up to me or is this normal.

Heat was from a 30 mile highway trip 2001 F250 4.10 LS with 37" tires no load.

Should I change the fluid and if so what is the best to use?
 
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Old May 7, 2007 | 06:38 PM
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The fluid is most likely 75w140, and you can certainly change it with (presumably) 200k on it, but I'm not sure how much difference that would make.
 
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Old May 7, 2007 | 11:52 PM
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From: Dinwiddie, Virginia
I don't want to change the fluid if I don't have to. If I have gotten this far with the diff I don't want to monkey with it now. It is still the best diff I have ever seen. I let a trans fluid change run long (75,000 miles) on a T-bird I had that was working good just changed the fluid because I was supposed too have already and it never rolled out the shop again until I replaced the trans.

For all I know the diff got this hot in the very first 30 miles I drove it. I have never felt it before so I don't know. The question is how hot is normal? If this is too hot for normal and shows a sure problem coming I have two options. I have the option of driving her till she comes apart and hope it dosn't lock up and wreck the truck when it does ( my normal plan of action ) or trying a simple fluid change now and hope it doesn't f up the LS when I could have gotten 100,000 miles more of fun out of it.

Any shops guys out there know what a proper functioning diff fells like to the touch?
Or maybe I just can't here the noise its making now over the M/T's and pipes.
 
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Old May 8, 2007 | 01:41 AM
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Doesn't sound too extreme to me. I've done the same thing and, yeah, they get hot. Sorry, no actual numbers for you.

The diff. temperature gauges I have seen go from 100-250 degrees...
 
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Old May 8, 2007 | 03:35 AM
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From: Dinwiddie, Virginia
Thanks tdister,

Depending on where the redline should be on those gauges it sounds like Im still good. I know you can't keep your hand on something a lot cooler than 200 degrees.

Anyone else got input?
 
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Old May 8, 2007 | 03:15 PM
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The threshold of pain when touching something is about 130*. Something that temperature would feel really hot.
 
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Old May 8, 2007 | 04:52 PM
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From: Dinwiddie, Virginia
Thanks gustang,
Sounds like I am worrying about nothing then. I just can't remember ever noticing the temp of a normal diff before in all my time under a truck. I have had to use welding gloves to change one before with the fluid boiling in it, but now that diff won't normal was it. Next 100,000 miles here we come!
 
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Old May 8, 2007 | 07:36 PM
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From: Saint Augustine, FL
Typical operating range for a diff is 150 to 200 degrees. I check mine regularly with an infared pyrometer. Haven't checked it much around town but towing on the interstate (5250 lbs van + 850 lbs of load + 3800 lbs of car/trailer) the temp typically stabilizes at 175 degrees. Never seen it below 150 on the highway and never over 190.

Steve
'95 Clubwagon XLT
 
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Old May 8, 2007 | 08:27 PM
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Thanks for the good numbers Clubwagon. I am just paranoid because I been doing a lot of bragging about the LS diff lately. Mind now at peace.
 
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