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Old 06-01-2010, 06:21 AM   #1
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1986 25' Sovereign
Gainesville , Georgia
Join Date: Sep 2009
Posts: 89
F250 Trans Cooler on Climbs Overlimiting...??

Hi friends. Two recent incidents that I need the forum's advice on.

1. Over Mother's day we towed our 86 SOV 25' CB up to Cloudland Canyon in GA. This is a typical "Appalachian" foothills climb. We were stuck behind a full dumptruck and were going about 10 MPH. I looked down at my trans temp and I was running almost in the yellow. I pulled over, let it cool and proceeded up the mountain with no issues. I figured it was because I was pulling a load slowly up a grade in 1st gear.

2. This past weekend we drove back to North GA from Gatlinburg, TN on Hwy 441 through the National Forest up over Clingman's dome (well, not over per se, but certainly through the gap that the highway traverses). I had to stop no less than 3 times to let my trans cooler come down out of the yellow back to "normal" temperature. We climbed this 3-4k feet mostly in 2nd gear at 35MPH. Surely a truck of this magnitude should NOT be having trans temp issues with a 6,000 lb load?

My first assumption is that my cooling circuit must be fouled? A check of my trans fluid yielded nice, pink liquid so I haven't "cooked" anything as I never ran it into the red.

Anything else that might be an issue I should have checked?

1986 Sovereign 25' CB - "Melody"

2001 Ford F-250 Super Duty 4x4 Crew Cab, 7.3L PSD

Air #41001
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Old 06-01-2010, 06:43 AM   #2
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Posts: 316
It would be interesting to know what actual temperatures the yellow segment on your gauge includes. In any case, the yellow implies that it is not in the danger zone, just that the operator should be aware that it's higher than what it is normally.

It is understandable that it was in the yellow zone under the conditions you described: going slow up an incline with a good load. Your transmission's torque converter was likely not "locked up" in those gears at those speeds, so it was slipping and thus creating heat. Also, at low speeds, there was not as much wind velocity to cool off the transmission fluid. Combined with the hill-climbing and the load, I would say it is expected that you would experience higher-than-normal temperatures.

I have a 1996 F250 7.3 Powerstroke with an aftermarket auto transmission temperature gauge, and I have seen it in the 220F or so range when climbing hills, although I have not been at the slow speeds you are reporting. That may be in the yellow zone too.

If you are ever worried about the temperatures, you could always opt for a larger transmission cooler. I've read that some folks have replaced the 7.3 cooler with those that are on the 6.0 Powerstroke engines. I have read they are much larger, and thus keep the fluid somewhat cooler under any given condition.

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Old 06-01-2010, 06:44 AM   #3
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2004 25' Safari
. , Illinois
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Posts: 10,336

You might check this out. My exp is that many of the OEM coolers and pans are not what they should be (not all and across all brands). I've towed at grade with this setup and though not at 10mph on grade for extended periods of time, I found these fairly simple and not overly expensive upgrades did in fact make a difference. I also switched to Amsoil fully synthetic ATF. I have yet to hit 200 degrees, though prior to these changes I would routinely get upward of around 190-195 degrees in at grade towing.
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Old 06-01-2010, 06:47 AM   #4
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2005 39' Land Yacht 390 XL 396
Common Sense , Texas
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Posts: 5,315

I would expect the transmission temp to go up on a long climb, cooler or not. At least, it always has on every vehicle I have ever owned.

The key I think, is for it not to get to the dangerously hot temperature, and GM at least, specs that temp to be 242 degrees.

I would check with a dealer and find out just how hot is "Hot" on your vehicle, and if you are not reaching that point, I personally would not worry about it.
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Old 06-01-2010, 08:32 AM   #5
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1971 25' Tradewind
Menlo Park , California
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I've had problems w/ this on our '96 4x4 F250 when we're forced to run slowly up steep hills towing heavy trailers. Since we have manual hubs on the truck, I've taken to running such climbs in 4 low w/ the front hubs disengaged on hard surfaces; this yields something like 2.7 underdrive and means we're climbing at 20 mph in third gear with the torque converter locked - and no heat issues.

- Bart
Bart Smaalders
Menlo Park, CA
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