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 > Coast on the uphills accelerate on the downhills

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drsteve

Michigan

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Posted: 01/07/20 06:38am Link  |  Quote  |  Print  |  Notify Moderator

And to think I get nervous when the trans temp exceeds 200...


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Hannibal

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Posted: 01/07/20 06:46am Link  |  Quote  |  Print  |  Notify Moderator

I just remembered my 2003 Cummins Ram with its 47RE transmission came new with a stuck closed torque converter anti drain back valve in the trans cooler line. This caused overheating in the trans. I assume GM uses a similar setup.


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Cummins12V98

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Posted: 01/07/20 07:41am Link  |  Quote  |  Print  |  Notify Moderator

At those temps most likely your transmission torque converter is not staying LOCKED.

Look into getting it to stay locked and I guarantee your heating issues will vanish.

Worst temps I have ever sewn on my truck is 172 in 100 degree weather at the top of a several mile 6% grade towing 35k combined.


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opnspaces

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Posted: 01/07/20 11:06am Link  |  Quote  |  Print  |  Notify Moderator

ACZL wrote:

Could always engage Tow/Haul or drop 1 gear and keep it there. RPM's may run higher, but you are drawing more air thru the rads and if eng fan kicks in, all the better for more air being sucked into eng compartment. Ironically this keeps tranny temps down and avoids shifting. Make sure you are running full synthetic for all oils as well.


Definitely in tow/haul mode, but not in the lower gears. I was under the impression that it only entered lockup in high gear. But if it will lock up in say second or third gear I can do that. I'll definitely try it next time out.


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opnspaces

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Posted: 01/07/20 11:09am Link  |  Quote  |  Print  |  Notify Moderator

Cummins12V98 wrote:

At those temps most likely your transmission torque converter is not staying LOCKED.

Look into getting it to stay locked and I guarantee your heating issues will vanish.

Worst temps I have ever sewn on my truck is 172 in 100 degree weather at the top of a several mile 6% grade towing 35k combined.


I definitely agree on the locked converter being the real key to this. And man I'm envious of your truck. If I had 865 lb of torque like your setup I could easily keep this combo in high gear.

dodge guy

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Posted: 01/07/20 11:37am Link  |  Quote  |  Print  |  Notify Moderator

Sounds like the axle ratio isn't suited for towing. It shouldn’t climb like that on moderate hills. Either the engine was lugging (wrong gear) or as you say you weren’t pushing it hard enough for the trans to kick down. I believe GM transmission lock up in 2nd.


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twodownzero

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Posted: 01/07/20 12:48pm Link  |  Quote  |  Print  |  Notify Moderator

It sounds to me like you were in overdrive and the converter was unlocking. Tow/haul mode and downshifting are in your future. There's no set of circumstances where it should ever get as hot as it did.

Grit dog

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Posted: 01/07/20 12:58pm Link  |  Quote  |  Print  |  Notify Moderator

I thought the older 4L80s only locked up in 4th gear, but some reading suggests that they also lock up at higher speeds in 3rd gear.
There are many relatively inexpensive lockup kits that allow lockup in 2nd, lower speed lockup in 3rd and 4th gears. Worth looking into, IMO.

That said, I don't believe that trans should have gotten near that hot towing what you towed in temperate weather.
Remember, they were originally designed to tow more than that without aftermarket parts.
Your new to you has 160k of unknown miles and treatment I'm guesisng.
Could be and likely is any host of issues that are contributing to trans heat. Cooler clean? fluid age/quality, bad lockup switch, worn converter, trans slipping a bit?
IMO, the primary issue is that something isn't 100% with the trans.
A cooler, a deeper pan, different driving habits may over come that, but you should be able to keep it cool in 3rd gear going up a hill.
(Disclaimer, I don't know the grades you were climbing, but presumably not "that" onerous if you've run the same older truck over it before without issue. It has a trans temp idiot light too.)


"Yes Sir, Oct 10 1888, Those poor school children froze to death in their tracks. They did not even find them until Spring. Especially hard hit were the ones who had to trek uphill to school both ways, with no shoes." -Bert A.

smarty

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Posted: 01/07/20 01:18pm Link  |  Quote  |  Print  |  Notify Moderator

would any of this "data" indicate the vehicle is exceeding its towing capacity?

ppine

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Posted: 01/07/20 01:42pm Link  |  Quote  |  Print  |  Notify Moderator

I can't agree with your technique at all. There is an rpm range that all engines pull best in. That is where you want to be. Gearing down and going slower will produce less heat.

* This post was edited 01/08/20 08:40am by ppine *

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