Friday morning I was on my way home from work in my 2007 Lariat with 118,000 miles and got stuck in one of the worst traffic scenes of the year. I idled/went under 5 mph for about 2.5 hours in the Houston morning heat. Amongst all the other cars and concrete around, my external temperature gauge was reading 103*. I also have a Gryphon programmer and regularly have it on the "transmission only" program (program 1) which only firms up the shift points as far as I know. Normally my TFT (trans fluid temp) reads around 150* but that day it was approaching 270 when the message center in my truck beeped at me and gave me a warning about my transmission (I wish I could remember the verbiage but I can't). My AC also stopped blowing cold around that time. Both of these problems I attributed to idling for extended periods of time amongst all that heat but my question is why would this happen to my 2007 vehicle and none of the other thousdands of vehicles around me, including my wife's 2000? Is there something I should look at to make sure everything is functioning correctly?

 

How old is the tranny fluid and the coolant? Remember, just because there's an auxiliary transmission fluid cooler, it still runs through the radiator. If the engine coolant is too hot, the ac condenser will not work as well, and the tranny will get hot too. Same goes for the tranny fluid. If it gets too hot, it can heat up the radiator. You might want to check your fan clutch also. It's not very effective at idle. If it's on its way out, that will cause everything to heat up more at idle.

 

Definitely check the fan clutch. When stopped in the heat, I often put it in neutral and bring the rpms up to around 1800 to get air moving through the radiator/coolers.

 

Did you drop it down to 1st or 2nd gear to keep it from hunting? What was the temp of the engine?

As lewissa81 asked, how old is the tranny fluid? It's possible although unlikely that debris from the tranny blocked the cooler line which caused it to overheat.

 

That's exactly why I'm not a fan of fan clutches. I switched to electric to avoid iOS (idle overheating syndrome)

 

I've been thinking of putting an auxiliary pusher in front of my rad./coolers just to help with A/C performance at low speeds. I'll probably just relay it to a small illuminated switch in the dash somewhere. I've never had any engine or trans temp issues but this would just make everything run that much cooler. In my case I'd be keeping the engine driven fan.
About 25 years ago I helped a friend install a Flex-A-Lite electric kit on a Chevy. It consisted if two fans (about 14" each) mounted diagonally in a custom shroud. The fans were on a progressive thermostat so one started at a certain temp and then the next one started about 15 degrees higher. One always ran when the A/C clutch was engaged. These were tractor (puller) fans that completely replaced the original, as you have done. This was a super sanitary installation and worked extremely well.

Sigman, I just looked at your signature, that's a pretty good chunk o' trailer your pulling. The biggest thing I pull with mine is a tandem axle boat trailer with a typical road weight of about 5300 lbs.

 

Thanks for all the suggestions guys. On that particular day my engine coolant was about 205 whereas normally it runs about 190. 205 isn't unheard of though. For the most part my engine coolant has been fine it's just the transmission fluid temp. What I'm noticing is that it seems if I'm doing a lot of idling or low speed driving, my TFT which is normally at 150 gets up to 170 or so but doesn't come down easily even when driving on the highway after. On the other hand, if I'm doing only highway driving, it stays normal. Wondering if my transmission cooler is not working right possibly?

Also regarding the age of the coolant and trans fluid, as far as I know it's the original fluid. What's the recommendation on the transmission fluid change? I see so many conflicting posts about flushing it vs not flushing it etc. that it's hard to know what's correct in this case. I'm fighting the same question about fluid change on my wife's 2000

 

If you are unsure of the fluid life, change it for peace of mind. As for the flushing debate, you will be safe if you look for a shop that has a non reverse direction pump that allows the transmissions own internal pump to flush the old stuff out and draw in the new fluid.

Forcing the flow backwards is not a good idea on an older tranny.

 

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That would definitely help AC and engine temps, but won't help the tranny at all. The tranny cooler is mounted away from the condenser directly behind the bumper which restricts airflow. It's in a bad location IMHO

 

Can someone explain to me how the cooling (engine) and transmission cooling system works (flow, order, etc.) on these engines with the factory auxiliary cooler?


Do I understand correctly that the transmission fluid routes through the radiator (but doesn't mix, of course) then through the auxiliary cooler? Is the radiator a colinear or counterflow type with regards to the engine coolant and transmission fluid? Which fluid is typically cooling the other (and obviously the air going through cools everything).


Having spent a few weeks with this problem now (with 0 time to do anything but check my transmission fluid level), I can safely say any time I am in stop and go traffic or idling for an extended period, my coolant jumps from 190 to 210 or so and my transmission goes from 150 to 200-210. It's a slow climb back down once I start moving again.