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Discussion Starter #1
I'd like to know what differential temperatures have been seen. What is normal and what is considered high. I would like to do this scientificly if possible by asking the following:

1. Gear ratio
2. Oil used
3. HP
4. Towing lbs (or hauling)
5. Was the temperature taken during steep grade climbs

Anybody?
 

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You will need more info. <ul type="square"> [*]Ambient temp [*]axle model, 10.25, 10.50, D80, ect. [*]speed [/list] [/list]
 

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Unless you catch somebody that just stepped out of a Peterbilt or Kenworth, there's not many of us towing with a pickup that have drilled and tapped our differentials for a temp sending unit.
 

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Mine was running about 212* out west with ambient in the 100* +- range, measured with an infared temp thingy. Standard 3.73 rear with factory fill of gear juice pulling a 5.4k TT.

Paul B
 

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I keep a strip of heat sensitive tape on my tranny pan and differential cover (10.5 Sterling) to monitor highest temp reached. My diff ran at 190 degrees for the longest time. On a trip through west Texas two years ago- towing a 9,000# TT - outside temps about 100 degrees, the tape on the diff recorded 210 degrees. That is well within the safe operating range of the synthetic lube and from what I've heard is similar to many of the big rig diff temps.
 

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In the summer my rear axle and manual tranny ran about 100 degrees above ambiant temp. It would go up a bit with long pull.
DENNY
 

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I don't know how accurate that and the other method is. I've had reason to drain quite a few truck rear ends when they came in loaded right off the highway (and crankases for that matter), and you could put your hand on the rear end housing and/or oil pan momentarily, but you sure couldn't touch the gear or engine oil, much, much hotter.
The temp of a thin auto trans pan I bet would be right on the money though.
 

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Sorry I don't have numbers but I can tell you that my truck runs hot when pulling. This is the first auto I have had in nearly 20 years, and due to not staying in OD, it runs hot very hot. The gauge (factory) has went all the way to just touching the red. i was towing nearly 18k (as I have many times with 7.3 and dodge with sticks of course) in about 98 degree temps (across south dakota). Now I can say it did not leave me stranded or actually overheat (meaning steaming or bursting out coolant) but it sure made me nervous. i would slow down and it would go back down, or the fan would kick in and it would go back down. But this stupidly designed thing, between the tranny shifting a million times and the fan not coming on until the gauage read 80% or better of the range before red, this thing could not make up its mind. anybody else deal with this?? I know of the people I spoke to on the road better than half say the same thing "just let off it'll cool down"...
 

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[ QUOTE ]
The gauge (factory) has went all the way to just touching the red. i was towing nearly 18k

[/ QUOTE ]

Wow, pulling 18,000 in hot weather, that's a lot to ask from your cooling system. Slightly off topic, but years ago I was talking to a Ford dealership diesel P.U. mechanic about my old truck running a bit hotter than I liked after installing an ATS kit. I cured mine with the later model bumper cut-outs, but he said, "You just think you got problems, I got an overheating P.U. in here, the owner tows 17-18K, his engine's slightly hopped up, (which puts a further demand on his cooling system), everythings in A-1 shape, a Ford rep said if these trailer mfgrs keep making them any heavier it's about time we traded places, they can make pickups, and we'll make trailers". I think he definitely had a point.
 

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Some of us DO have drilled and tapped stuff to monitor rear axle (and main trans, and aux trans) temps. The D80HD in my sig truck generally pulls at a gross between 34 and 36k. I listened to an awful lot of alarmist stuff about excessive temp burning the paint off of the housing, and, having lost two rear axles under warranty, and then another afterwards, I decided there MUST be some truth to that bother. When I got back to my own shop, I drained the new axle (a month or two later) and got about a half quart of WATER. Now, axles that can burn the paint off don't have water in them!. I had already built the 1 1/2" finned aluminum extension with the magnetic drain bung, filler hole, dipstick and oil temp probe, so in it went. I monitor the temp to use as a load indicator for testing the aux trans. I use the same amplified oil temp gauges for all three, beginning at 140F and ending something like 320F. Well, on level ground in anything but summer temps, the rear axle will never get off the 140F lower peg. It takes a wicked climb at 80-90F in the Rocks to see the max (170 or so) that I have ever recorded.

Oh yeah, I solved my water problem by re-routing the breather line. The current R&P has more miles than the previous three.
 

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Discussion Starter #12
I think this is all good information and a learning experience that towing can really up your diff temps. I talked to two diff shops today and asked them what temps they have seen. Their answers were basicly the same. Both of them said that normal diff temps are between 140 and 190 deg F depending on your axle ratio. A 4:11 gear will run hotter than a 3:73 or 3:55. Towing adds more temp and normal for less than 10K towing is 200 to 230 deg F. Both of them also stated that they have seen temps of 280 to 320 deg F when towing 18K to 20K. God knows what temps they guys see if they are going up a grade with 4:11's and towing 30K. This is great info I'd like to learn more.
 

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[ QUOTE ]
I don't know how accurate that and the other method is. I've had reason to drain quite a few truck rear ends when they came in loaded right off the highway (and crankases for that matter), and you could put your hand on the rear end housing and/or oil pan momentarily, but you sure couldn't touch the gear or engine oil, much, much hotter.
The temp of a thin auto trans pan I bet would be right on the money though.

[/ QUOTE ]

In engineering circles that's known as "letgo temperature".
 

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Yeah, I kind of think its a bit much to ask, but thing is I have done this for many years, with a stick and never even had an issue. So it kind of burns me when Ford (a company I have loved and trusted for many years) says this is the better way to go (meaning the auto tranny) instead of just letting customers get what they want and have used for years. Sorry a bit off topic too.
And a little FYI, if you did know, many people pull what I pull. anytime you see those big campers with three axles, they weigh in at or near that.
 

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I do have a temp gage on the differential. I have the Mag Hytek cover, 4:10 gear and run synthetic gear lube.

I pull trailers weighing up to about 15,000lbs. The temp reads just about 100 degress over ambient temperature. Temps are very consistent and dont vary much at all. I do however pull on mostly gentle grade roads but very high winds sometimes.
 

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Discussion Starter #16
Thanks for the information, however using a Mag-Hytec is cheeting. Those things will hold twice the lube and cool temps over stock covers. I'm looking for temps seen with stock diffs. I did a quick check on temps and how to tell what temps you have. 140 deg is like holding a cup of coffee. You can hold you hand on 160 but not for long. at 190 you don't want to touch unless it's a fast touch. If you spray or pour water on the diff and it sizzles it's higher than 212 deg. Over than I'm sure if you touched the diff you would leave skin on the diff. I can't figure out an easy way to get high temps like 250 to 320.
 
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