Heading to Lakeland, Florida, from Fort Lauradale ,Transmission 7 AM,4-hour trip, Hot on display came on, temp was 280 on Trans gauge, was going 75-80 on turnpike, had been driving for 1 1/2 hours at 90 degrees outside, water temp was 200 degrees. The transmission was rebuilt 25,000 miles ago and has never got hot before, though its the first time i have ran it down the turnpike since the last rebuild, has never had a shifting issue in the last 25,000 miles, we pulled off turnpike and it immediately went off and the trans gauge and slowly returned back to normal range of 200 degrees, in about 20 minutes at idle, canceled trip, went back home via US1, just in case it overheated again. The 4 hour drive back home it never went over temp of 200 on transmission gauge, it shifts fine, does not act like anything had happened, do i need to add a fan on the stock H2 trans cooler, or add another cooler to it, i had asked about an additional cooler for the transmission and they said it wasn't needed, fluid is clean and red and full on stick.......had 37-12.5 M/T tires on it at rebuild, they sid it wasn't a problem,,,,,,,

Do i need a fan cooler or another cooler added to stock transmission cooler, suggestions?

2004H2
2006H3

 

Sounds like you have a problem. Try checking to cooler and cooler lines to see if they’re clogged. Your torque converter could also be going out of the above doesn’t solve it. You’d have to look at live data to really tell. Is there any shuddering happening? Can you tell when it locks and unlocks?

 

a fan will not help, there are no fans that can move the amount of air that is going across the cooler at 70 mph, if it were getting hot at low speeds in town then a fan might help.
I personally don't think an aux fan does much if any good as the radiator fan is pulling air across the cooler already.
Its usually a requirement that the cooler and lines get flushed and tested when the trans is rebuilt as part of the warranty, I wonder if they did.
I've read that some trans allow some of the fluid to bypass the cooler while in OD, next time the temps on the trans start coming up take it out of OD and see if it cools down.
I'm with Gavin on this one you may have an issue with the trans or the temp sensor in the trans,

Neal

 

shifts fine, no shutter, runs perfectly normal, temp stays at 200 degrees around town and on turnpike and I-95 for 19-20 mile trips ….called transmission shop, they suggested an additional cooler, or a electric fan on the present cooler…when I stopped the cooler was hot, when the gauge was at 280….

 

I bought a 7” electric cooling fan, 800 CFM, going to try it out and see what happens, there’s hardly any space between the hood frame and the trans cooler, this looks like it will fit snugly, last year had a new Aluminum radiator put in, wouldn’t think that would be an issue, Amco said it would be hard to figure out why the overheating on highway because it doesn’t do it in city driving,they put there tester on it everything normal, no codes, also suggested replace cooler with a Brand new unpainted one, the black paint cooler holds in the heat, where the aluminum cooler dispels it….I’ll keep you updated on the progress…

thanks for input….Rick

 

First, replace the transmission fluid ASAP since you cooked it!
The optimal temperature range for transmission fluid is 175 to 220 degrees. Above that, for every 20 degrees, bad things happen, starting with the formation of varnish at 240 degrees, followed by seals hardening, plates slipping, seals and clutches burning out, carbon being formed, and, ultimately, failure.
Then find the source of fluid flow restriction!
A hot transmission may be the victim of a faulty or failed solenoid. A solenoid is an electro-hydraulic valve that regulates the fluid flowing into and out of the automatic transmission. If the solenoid goes bad, then the amount of transmission fluid flowing will not flow properly — leading to a transmission overheating and potential failure.

Start here:

FLUSH before you change the fluid & FILTER! #seafoamworks



Refill with DEXVI

 

So....I am under the impression that the tranny fluid runs into the right hand Rad tank. Thru a coil then back out. At least it's that way on m 09. So the mention above about Lines to and from the tranny are in play. So any clog problems in that side of the rad tank could limit cooling around the tranny Fluid coils. BWTFDIK

 

I would follow the shops recommendations then see if it corrects the issue.

Neal

 

I installed the true cool large external cooler bypassed the built in to radiator one, it's barely moved temp Guage even on hottest days, I'd recommend it to everyone, there's a few threads on installing this one, old threads

 

If its indeed overheating then an external cooler could help. As legerwn said though, a fan will do nothing at all unless its overheating when going under about 30mph. Above that speed even factory electric fans shut off since they are pointless when the air moving at speed is far greater than what a fan can provide.

I suspect a failing sensor or possibly a clog somewhere though.