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Normal Trans Temp? - 2500hd Gmc 4l80e


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#1 Billdog350

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Posted 30 April 2007 - 09:29 PM

Guys, I've had manual trans trucks for the past 12 yrs, this is my first automatic and i'm already regretting it. It's a 2003 GMC 2500HD with 133,000 mi. The 4L80e tranny blew shortly after I purchased it ($3 thrust bearing went which caused a significant failure). The dealer (non-gm) rebuilt it under CT warranty law. Approx 2500 mi later my transfer case went which I had to pay to replace with a junkyard unit. Of course the 133k mi isn't helping.

Regardless, now that the tranny has been rebuilt, I think its running hotter than usual. Before the rebuild (granted it was the middle of winter) it never got above 110-120 deg according to the gauge.....Now when I'm driving with ~60 deg ambient the tranny gets up to about 150 deg and when its sitting in place idling for long periods it will climb up to around 200 (close to coolant temps).

I just towed a 5000lb trailer to VT, averaging 70-75mph even with steep hills and I didn't notice any abnormal behaviour and the temps didn't climb above 200 deg (with ~65 deg ambient).

I know the radiator has a tranny cooler in it, as well as an external tranny cooler. Both were supposedly flushed.

My question is: What are normal transmission temps?

#2 HD Sierra

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Posted 01 May 2007 - 01:53 AM

NOt sure how much help I can be as I just bought my truck and have not towed with it yet...on <60 degree days, the tranny temp sits about 110-125 or so...yesterday was 91 here and it got to about 150 and never went over....agian, this is not towing...highway and city combo...
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#3 Coachmenguy

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Posted 01 May 2007 - 02:06 AM

i know towing my 30ft TT i've never seen it above 200, which is midrange on the gauge, in the winter with no load it just lifts off the cold(100 degree) mark, this time of year i've seen around 130-140. On my 96 with the 4l80 i put a digital gauge on that and it almost always ran 120-130 on the e-way, hope this helps
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#4 Shaners

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Posted 01 May 2007 - 01:43 PM

I'd say your temps are fine... My '01 had the 4L80E and it's temps were very similar. In fact my Allison tranny in this truck runs about the same too.

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#5 Billdog350

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Posted 01 May 2007 - 01:59 PM

Thanks for all the replies guys! Looks like ambient temps have a huge impact on trans temps (makes sense) and I'm pretty much in line with what others are seeing.

I guess my final question is: Is it normal for the tranny temps to climb when you're idling? I would guess there would be heat soak from the radiator at some point....just seeing if others have the same too.

#6 2500HD 8.1

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Posted 01 May 2007 - 05:42 PM

Mine normally is right under 150. It does creep higher when the outside air temps are high.
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#7 Shaners

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Posted 01 May 2007 - 07:04 PM

If you are idling then you aren't getting any cool airflow through the cooler.

If you are in gear and idling (like stuck in stop and go traffic) then the heat would build up even faster.

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#8 wht2500hd...

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Posted 03 May 2007 - 03:05 AM

200 at idle is not normal unless you had towed in traffic (or if you have electric cooling fans). the external cooler cools mostly at highway speeds. check the fan clutch and engine cooling temp (if you don't have electric fans). make sure trans lines were not criss crossed at radiator (not likely.)

(at idle) radiator fan spins slowly when engine is cold or ambient temp is cold; fan spins fast when engine is hot or ambient temperature is hot. That is the visual test only for the fan clutch. on the hottest day (90 degrees) you will hear the roar of the fan when the clutch applies maximum grip to the fan when accelerating from a stop.

if you have electric cooling fans then turn on a/c and see if trans temp drops (while idling;) if it does then 200 degree idling temp is normal.

check engine coolant level.
check again the color of the trans fluid.

HD's have massive cooling capacity.

Edited by wht2500hd..., 03 May 2007 - 03:09 AM.


#9 HDdave

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Posted 03 May 2007 - 05:28 AM

My tranny in my 01 will run right around 140 in normal driving..
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#10 Billdog350

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Posted 03 May 2007 - 07:38 AM

200 at idle is not normal unless you had towed in traffic (or if you have electric cooling fans). the external cooler cools mostly at highway speeds. check the fan clutch and engine cooling temp (if you don't have electric fans). make sure trans lines were not criss crossed at radiator (not likely.)

(at idle) radiator fan spins slowly when engine is cold or ambient temp is cold; fan spins fast when engine is hot or ambient temperature is hot. That is the visual test only for the fan clutch. on the hottest day (90 degrees) you will hear the roar of the fan when the clutch applies maximum grip to the fan when accelerating from a stop.

if you have electric cooling fans then turn on a/c and see if trans temp drops (while idling;) if it does then 200 degree idling temp is normal.

check engine coolant level.
check again the color of the trans fluid.

HD's have massive cooling capacity.

I have a clutch fan and I have suspected that it might be defective, I'll have to do some more testing. I'll also have to see if those trans lines could have been criss crossed. As soon as the vehicle stops you can start to watch the temp gauge start rising (towing or not). My concern is that it rises while in PARK which shouldn't be putting strain on the torque converter and thus generating heat. I understand air flow and head soak...I just find it interesting that my friends 2500HD and 3500 don't increase in temp at all while idling and mine does...we all have stock motors and fans so its all apples to apples. My engine temp never rises above 190 but occasionally dips to 160 while on the highway according to the gauge...not sure what's up with that.

FYI, most clutch fans are actually a viscious clutch, similar to the Subaru AWD system. When the fluid temperature changes, it becomes thicker and thus "engages" the clutch. Once it cools, the fluid becomes thinner and the fan starts to freewheel more. It's really a cool technology...no moving parts, just fluid. I'll have to see how much a new fan clutch will cost, at 130k mi it might be time anyway.

Coolant is topped off and fine. Fluid level/smell/color has been checked and re-checked and was just changed with the filter less than 4000 mi ago when the tranny was rebuilt, and again about 2000 mi ago when the transfer case went (I wanted to make sure the tranny was ok while it was on the lift).

Edited by Billdog350, 03 May 2007 - 07:40 AM.





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