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Old 07-30-2020, 01:19 PM   #1
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Towing Temps

2500 Duramax LMM / towing 9,000#
OAT80-85*F
The slightest grade truck temp goes up to 225*
Both indicated by dash gauge and edge monitor.
Fan clutch only started to engage at 232*F+
I took the thermostats out and put in hot water to test them.
Ratings: 180 + 185*F
They opened at 195 + 200*F
Great problem found...
I got new tstats and tested the same way.
They opened at 190 + 195*F
Poor Accuracy!
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Old 07-30-2020, 01:27 PM   #2
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On the new tstats, is there any marking on them indicating the opening temp?
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Old 07-30-2020, 01:39 PM   #3
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Yes
80C + 85C
= 180F+ 185F
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Old 07-30-2020, 01:49 PM   #4
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225 is fine. With the fan coming on at 235 proves 225 is good to go. Those gauges are not that accurate.
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Old 07-30-2020, 02:13 PM   #5
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The Edge monitor reads right off of the ECM...
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Old 07-30-2020, 04:21 PM   #6
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You don't tell us the year of your truck or many other details. This makes a big difference. If you have a 2001 2500 Duramax, then this might be a problem. If you have a 2020 2500 Duramax, then this isn't a problem.

Transmission temps are much different today than they have been in the past. The old conventional wisdom no longer holds. 230 used to be very hot. Now, not so much.
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Old 07-30-2020, 04:32 PM   #7
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Quote:
Originally Posted by mfMcFroggierPod View Post
The Edge monitor reads right off of the ECM...
The PCM only sees reference voltage from the coolant temperature switch and even those switches have a ± variance.
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Old 07-30-2020, 04:47 PM   #8
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What details? A LMM gives a good reference year spread ‘07 Chevy Ext Cab 6’6” bed 6.6L 4x4
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Old 07-30-2020, 04:48 PM   #9
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Might as well put idiot lights back on the dash and no gauges if they are off so much.
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Old 07-30-2020, 04:57 PM   #10
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I have an LBZ, 2007 classic. My fan engages at about 215. Climbing long steep hills with my 11.5k fifth wheel it rarely gets to 220. When it started getting to 235 on a 100 degree day on those same hills, I had the radiator flushed and outside cleaned. Back to normal. Also, on very hot days I will put it in manual 4th gear and keep speed under 50 for steep climbs. Seems to hold temps down very well doing that.
You might have the fan clutch examined, as it should come on much sooner in my opinion.
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Old 07-30-2020, 05:09 PM   #11
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Tx for the info.
It is all of the crap emission equipment. I had a 07 Classic an no problems towing a trailer similar to your size. A fan clutch was my next thought. I replaced the tstats because of no way of knowing if both are working properly...
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Old 07-30-2020, 08:35 PM   #12
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Quote:
Originally Posted by NMWildcat View Post
I have an LBZ, 2007 classic. My fan engages at about 215. Climbing long steep hills with my 11.5k fifth wheel it rarely gets to 220. When it started getting to 235 on a 100 degree day on those same hills, I had the radiator flushed and outside cleaned. Back to normal. Also, on very hot days I will put it in manual 4th gear and keep speed under 50 for steep climbs. Seems to hold temps down very well doing that.
You might have the fan clutch examined, as it should come on much sooner in my opinion.
This is usually done only when tow vehicles start to look like they're powered by steam.

It's a good idea to have the cooling system flushed regularly and coolant replaced. Also helps to treat cooling systems like batteries and only mix coolant with distilled water---------or purchase pre-mixed coolant of your choice. "Hose water" can vary around the country from no minerals to extremely mineral laden which will plug the radiator in a short time.

My personal choice is to service Tranny and Cooling system every 50,000, Just my choice and others may choose longer intervals but the point is ----Change these fluids. They don't last forever.
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Old 07-30-2020, 08:51 PM   #13
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Quote:
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This is usually done only when tow vehicles start to look like they're powered by steam.

It's a good idea to have the cooling system flushed regularly and coolant replaced. Also helps to treat cooling systems like batteries and only mix coolant with distilled water---------or purchase pre-mixed coolant of your choice. "Hose water" can vary around the country from no minerals to extremely mineral laden which will plug the radiator in a short time.

My personal choice is to service Tranny and Cooling system every 50,000, Just my choice and others may choose longer intervals but the point is ----Change these fluids. They don't last forever.
GM radiator flush interval with Dexcool (premixed)is 5 years or 150k miles. I do it every 100k.
My cooling was degraded mainly due to crap built up in the radiator fins. Bugs, assorted trash. Took it out ,cleaned it real well, straightened fins... Good as new
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Old 07-30-2020, 08:59 PM   #14
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Originally Posted by NMWildcat View Post
GM radiator flush interval with Dexcool (premixed)is 5 years or 150k miles. I do it every 100k.
My cooling was degraded mainly due to crap built up in the radiator fins. Bugs, assorted trash. Took it out ,cleaned it real well, straightened fins... Good as new
You do have some bugs in your neck of the woods, depending on season
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Old 07-30-2020, 10:17 PM   #15
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A 185 stat begins to open at 185 (plus or minus a few degrees). They do not typically go fully open until 15 degrees above their rated temp.
Different trucks, but I regularly see 220 on the coolant and 230 on the oil. That is just on the interstate when it is 95 outside.
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Old 07-30-2020, 10:30 PM   #16
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GM has an issue with the fan clutches anyway. Change it with a new A/C delco towing clutch you won’t be sorry.
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Old 07-30-2020, 10:33 PM   #17
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Also if you experience the temp getting above 220 turn your heat on and roll the windows down till your off the pull. It will bring the temp right down!
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Old 07-30-2020, 10:35 PM   #18
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I change my coolant fairly often. On my old trucks, it was every 50K and I only use distilled water if I am required to mix. On my new truck it was at 30K and going to be every 60K after since I have to drain the coolant when I drop the transmission pan.
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Old 07-31-2020, 03:20 AM   #19
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Great Info from everyone, Thank You
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Old 07-31-2020, 07:50 AM   #20
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One more thing. Have you looked at the cooling stack for debris build up between the cores? Stuff likes to build up between the trans cooler (front one) and the AC condenser which blocks flow to the radiator on that side.
Also, had the coolant changed recently...or ever? Diesels put a beating on coolant.
Edit- cooling stack is the multiple radiators up front.
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