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#2299890 - 06/27/11 09:58 PM How hot does the gear oil get in a GM rear end?
Loobed Offline


Registered: 07/20/07
Posts: 3742
Loc: Northern California, USA


Does anyone know what the upper operating temperature of the gear oil in a GM truck rear end. It is an 8.6" 10 bolt, but I would guess all sizes are close to the same temps.

thanks
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#2299922 - 06/27/11 10:28 PM Re: How hot does the gear oil get in a GM rear end? [Re: Loobed]
dparm Offline


Registered: 04/19/10
Posts: 11812
Loc: Lombard, IL
For what kind of duty? Daily driving? Off-roading? Towing? Racing?
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#2299944 - 06/27/11 10:51 PM Re: How hot does the gear oil get in a GM rear end? [Re: dparm]
MetalSlug Offline


Registered: 07/24/10
Posts: 2032
Loc: Garland, Texas
Originally Posted By: dparm
For what kind of duty? Daily driving? Off-roading? Towing? Racing?


why you would include " racing " leave that out lol. its a truck.

what year is the truck ?
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#2299951 - 06/27/11 11:01 PM Re: How hot does the gear oil get in a GM rear end? [Re: Loobed]
Gene K Offline


Registered: 01/25/03
Posts: 3127
Loc: Decatur AL USA
Originally Posted By: Loobed


Does anyone know what the upper operating temperature of the gear oil in a GM truck rear end. It is an 8.6" 10 bolt, but I would guess all sizes are close to the same temps.

thanks



Ambient temp and load would play into it. It will run much cooler in town empty at 60F ambient than pulling a 20 mile long 3% grade in 120F heat grossing 14,000 lb with a trailer. Condition 1 might be 120F and condition 2 might be 280F.


Edited by Gene K (06/27/11 11:04 PM)
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#2299970 - 06/27/11 11:29 PM Re: How hot does the gear oil get in a GM rear end? [Re: Loobed]
Loobed Offline


Registered: 07/20/07
Posts: 3742
Loc: Northern California, USA

It is a 2001 GMC Sierra 1500 4WD (1/2 ton).

I am driving mostly around town and on the highway with an empty bed. I might drive 2 times a year to the mountains (150 +miles one way) fully loaded, with a little of road dirt trail driving in 4WD. I have not towed in 8 years, and I don't expect to tow in the near future. No racing.
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Engine: 2001 GM 5.3L LM7
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#2299987 - 06/28/11 12:39 AM Re: How hot does the gear oil get in a GM rear end? [Re: Loobed]
ARB1977 Offline


Registered: 06/12/05
Posts: 4401
Loc: North Texas
Loads, outside temps and how much oil is in the diff... so really its hard to say. Run synthetic or dino and proper viscosity you'll be fine.
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#2299990 - 06/28/11 12:43 AM Re: How hot does the gear oil get in a GM rear end? [Re: Loobed]
Gene K Offline


Registered: 01/25/03
Posts: 3127
Loc: Decatur AL USA
Originally Posted By: Loobed

It is a 2001 GMC Sierra 1500 4WD (1/2 ton).

I am driving mostly around town and on the highway with an empty bed. I might drive 2 times a year to the mountains (150 +miles one way) fully loaded, with a little of road dirt trail driving in 4WD. I have not towed in 8 years, and I don't expect to tow in the near future. No racing.



Maybe 200F.
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#2300000 - 06/28/11 01:15 AM Re: How hot does the gear oil get in a GM rear end? [Re: Loobed]
Bluestream Offline


Registered: 09/13/03
Posts: 3613
Loc: Waterloo, ON
Next time put your hand on your diff after driving around. You will have your answer...
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#2300007 - 06/28/11 01:33 AM Re: How hot does the gear oil get in a GM rear end? [Re: Bluestream]
tinmanSC Offline


Registered: 09/07/10
Posts: 1825
Loc: Oswego, IL
Originally Posted By: Bluestream
Next time put your hand on your diff after driving around. You will have your answer...

Ouch!
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#2300631 - 06/28/11 04:10 PM Re: How hot does the gear oil get in a GM rear end? [Re: tinmanSC]
Bluestream Offline


Registered: 09/13/03
Posts: 3613
Loc: Waterloo, ON
Originally Posted By: tinmanSC
Originally Posted By: Bluestream
Next time put your hand on your diff after driving around. You will have your answer...

Ouch!


If its that hot to burn you hand you have real problems. Mine never gets past warm...
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1999 Grand AM 2.4 A4
2000 VW Beetle 1.8T M5
2000 Ford Explorer 4.0 4X4
1991 BMW 735iL
"A fool and his money are soon parted" - Thomas Tusser

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#2301049 - 06/28/11 11:39 PM Re: How hot does the gear oil get in a GM rear end? [Re: Loobed]
mechtech2 Offline


Registered: 09/05/06
Posts: 19479
Loc: Chicago Area
A lightly loaded rear end should be from ambient to maybe 150F or so.

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#2301174 - 06/29/11 07:21 AM Re: How hot does the gear oil get in a GM rear end? [Re: Loobed]
Jim Allen Offline


Registered: 08/12/05
Posts: 4477
Loc: NW Ohio
The 8.5 (an older generation of your 8.6) in my old diesel Blazer ran around 180-200F in 80-90F ambient, lightly loaded, with 4.10 gears and a Detroit Locker installed.

Smaller ring gears in axles with small oil capacities generate some pretty high temps with heavy loads. Also, lower gears run hotter than high gears. The rules of thumb I was given (and have largely observed) is around a 10-15 degree spread between 3.08 gears and 4.10s. This has to do with the taller gears having more tooth contact, spreading the load over a larger area, and they run a little cooler.

The faster you go the hotter the diff also.
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#2301493 - 06/29/11 12:58 PM Re: How hot does the gear oil get in a GM rear end? [Re: Loobed]
mechtech2 Offline


Registered: 09/05/06
Posts: 19479
Loc: Chicago Area
Jim - That's kinda hot for a lightly loaded rear end.
That 4.10 is part of it.

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#2301549 - 06/29/11 01:49 PM Re: How hot does the gear oil get in a GM rear end? [Re: mechtech2]
Jim Allen Offline


Registered: 08/12/05
Posts: 4477
Loc: NW Ohio
Hey Mechteh- It's in line with what I have seen elsewhere and on my current trucks. Probably should have mentioned that my numbers are obtained by running at a steady freeway speed for as long as it takes to stabilize the oil temp. Sometimes that takes 15 miles or so. Running around town at 35-50 mph knocks 20-30 degrees off that. Some of that temp is load from windage (and that lifted Blazer was a brick). Some of the extra heat is compensated for by air cooling, I suppose. Anyway, it was what it was and may not apply to anything else, though I've found a lot of correlation bin gear ratios, ring gear size, oil capacity and load.
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