Overheating in tow

[advancesafari]

I have a 1992 Safari/Astro van 4.3L "Z" code non Vortec engine. I'm having an overheating issue @ highway speeds.It runs hot within 10 mins of being on the highway . I'm pulling a 3500lb. trailer. The van has a new waterpump and fan clutch "severe duty" didn't make a difference. I need help!! Plz. Only happens while towing.

[astrozam]

Do you have an aux tranny cooler installed?

[advancesafari]

No will this coolant temps to rise?I was planning on installing 1.

[astrozam]

Not having an aux tranny cooler puts alot of extra load on the tiny oem tranny cooler that is attached to the side of your rad, this causes additional heat load on your engine coolant ( because that coolant is used to cool your tranny oil )

Another thing, are you towing thru mountains, level road? this makes a huge difference ( especially if you don't have an aux tranny cooler ) Are you in overdrive or 3rd gear ? rear-end gearing and tire size also plays a factor but the problem is most likely due to the fact you do not have an aux tranny cooler.

[advancesafari]

Flat with mild hills I'm not sure "no tag on diff."on gear ratio.In 3rd

[astrozam]

3rd is a good safe gear to be in, don't be overly concerned with the gear ratio ( it was just an additional thought ) at the moment. Install the largest aux tranny cooler you can, there are several threads with the info on how to do this such as this one...viewtopic.php?f=5&t=514&hilit=Aux+tranny+cooler+install

[advancesafari]

Thx I hope this solves the problem

[astrozam]

Your welcome, I believe it will def help you.

[Cobra]

couldn't it be a thermostat issue as well I've towed without a tranny cooler in overdrive for 600km (never do this) and my engine didn't overheat.
another thought is do you have anything blocking the grill if the air flow through the rad is restricted it's possible you won't notice the problem until under heavy load

[LiftedAWDAstro]

I too would say it a coolant flow issue. Either the t-stat is plugged or partially malfunctioning or your radiator is plugged. My money will be on the radiator. I agree with Zam though. Get the largest trans cooler you can afford because the tranny will cost a LOT more to replace than the cooler. You can also get a heavy duty radiator if you need to replace it.