I have been searching and trying to find an answer for this on multiple sites, but no luck. I have had the swap done for over a year and a half now, but every time I drive on the highway in excess of 65 when its 110 out the thing will get to 250 degrees, as verified by the dash gauge and the GM PCM. As soon as I pull onto the side of the road it quickly cools down to about 220 within a minute.
I I will add after a night of wheeling driving home at 70 or so the temps will not go over 215. I can crawl around all day at the mall and it doesn't get over 210 as well.
And all the basics have been covered, new water pump, new 195 t-stat, its not running lean, no air in the system......etc.
Some specs, 2001 TJ with 2002 5.3, 4l65e, Novak radiator, Novak spal fan with shroud. The fan is controlled by the pcm, but of course on the highway with the temps staying so high the fan never shuts off.
It has to be down to a airflow problem at speed interfering with the running fan. I even tried a new shroud that Novak sent me with 4 trap doors on it, and driving it without the winch on but still no luck. So has anyone tried installing a switch that will shut the fan off while going down the highway, or do you think that will even work? I'm at a loss at this point.

 

Typically cars shut off electric fans once the vehicle goes above 40 to 45mph. Are you missing an air dam? At highway speeds if an air dam is missing that can cause overheating.

The fans should not be running at highway speed it impedes airflow and will cause overheating.

 

That's what im thinking as well. Is there a way for the pcm to cut signal to the fan above a certain speed via the vss? When I had my harness redone there was only one wire to hook up to the relays for the fan, and I don't know if it was ran to the pin outs for fan 1 or fan 2, if that matters. Thanks.

Also the rad is sealed tightly against the core support.

 

The PCM should be shutting the fan's off based on the output from the VSS. How it does this though I am unsure and someone who knows the harness and pin outs would have to chime in.

 

Um, hate to ask, but are the fans moving air in the correct direction? Just ran across this in another car.

 

I agree with the fan suggestion, wait for them to come on and see which way they're blowing. If it's wrong just switch the negative/positive wires to your fan

 

Its definitely pulling air. It will hold a towel over the grill on its own.

 

Maybe try and pull the fuse to your fans and go on a highway run to eliminate the fans as your problem. Really weird, usually overheating happens in stop and go/slow driving not when there is 60mph airflow (5000+CFM per square foot of radiator) hope you get it figured out.

 

I am unsure and someone who knows the harness and pin outs would have to chime in.

 

I remember awhile back Stu-Cool had this problem on his LS-swapped Stude. I may be wrong, but I think he traced it to the heater core loop in which he was using a blocking type valve to stop flow through the core. This caused no issues around town, but on long uphill pulls the engine would overheat...

 

Did you figure anything out?

 

ATGORG, please update us with your progress.

As this is a Jeep conversion, your questions would be better answered in the conversions section.

 

Any updates? Having the exact same issue with a 5.3 in a TJ, same company for shroud,radiator, etc...

 

One possibility:
https://ls1tech.com/forums/generatio...nd-u-hose.html

 

Thanks for the link, good info there. I don't want to hijack the thread so I will be starting a new one.

Hope the OP got his situation figured out, hope to hear his results.