Transmission runs hot only when towing

[Steven Schutz]

2012 Silverado.  350,000 miles. Replaced original trans at 217K with OEM that had to be rebuilt at 107K. Heavy duty radiator installed 3 yrs ago.

Truck is a work truck, high mileage and pull a utility trailer daily on 200-300 mile roundtrip on mostly flat terrain. Trailer usually has Pioneer 1000 and Recon. Total weight of trailer and load is 3000#. Transmission will climb to 190-205 quickly, even if trailer is empty. No load temp is 175-180. Temps never got this high in the past. No CEL. Truck itself does not run hot, constant 210 or a tad lower. Tran mechanic and motor mechanic can't find any real issue. I may clean or even replace radiator again.

Any thoughts?

TIA

[CamGTP]

Hard to say because the temps you are seeing are totally normal and within the spec of the transmission.

 

Put an external cooler on it if you want it to run lower temps.

 

And just a for your information, the gauge cluster lies about the coolant temp. The 210 mark is really 195ish degrees if you use a scan tool to read the coolant temp sensor. Showing 210 was easier so that when the temps actually start to climb the gauge doesn't move until temps are rising above that and people won't freak out right away.

[Steven Schutz]

Ok, I see different info online (I know)...some, like me, get nervous at 200, others feel fine at 230. 

I am concerned because I do the miles daily. Thanks for your input.

 

[txab]

As Cam mentioned, larger external/secondary cooler. Plus I'd use a high quality true synthetic fluid like Amsoil or similar