04 2500HD 6.0 Strange towing issues!

CTM · August 23, 2017

We bought a 7'X14' 7000lb cargo trailer for our move to Florida from NY. The truck is a ext.cab, long bed, 4X4 with approximately 117K miles on the odometer.

The last repair that the truck had was a new water pump, and fan clutch just before we left.

Everything was fine for the first several hundred miles, then several thing started to act up.

The outside temps were in the mid 80's to low 90's, and we only stopped for gas and bathroom breaks most of the trip. I was driving the speed limit most of the way, 60>70 mph.

The first thing I noticed was that the trans temp stayed at 200 degrees, but the transmission started to shift abruptly and clunk when passing and coming out of a lower gear. Then next thing was a loud whining sound getting louder and higher pitched the faster you accelerated, sort of sounding like a belt or some type of bearing noise.

I immediately stopped and check all the fluids, belt, and looked for leaks. At idle, the engine sounded perfectly normal, bring up rpms and the whine would start, but couldn't tell from where.

All the gauges were normal, and the truck seemed fine. I decided to continue. No loss of power for the next several hundred miles, including going up lots of mountains. Then the engine light came on and went out in about 50 miles.

Believe it or not, I completed the 1200+ mile trip without breaking down!

Now here is the strange part. I unhitched the trailer at my destination, and the next day took the truck out, and it drove like none of this ever happened! The transmission shifted normally, temp was around 170, no clunk, the whine was not there, for the most part. I did notice a slight sound after about 20 miles, but nothing like it was on the trip.

Anyone have any idea about what happened? I would think that the truck couldn't heal itself, and if something was going to fail, it would have happened in the 1200 miles!

Formulabruce · August 23, 2017

I would consider Replacing the stock trans cooler with one at least twice the size. Pretty easy to do, and use the stock lines.

I personally, when making a long tow in the summer where its going to be above 90 will pop on my 160 T stat in the cover of the lower radiator hose water pump outlet. This can be done from underneath, and if you have the 160 T stat in hand, and coolant isnt too hot, you can do this with only loosing about a gallon on the ground as the T stats have their own gasket.

Did the People replacing the Water pump, re install the Old Thermostat?

If I was moving to Florida, I would just Leave the 160 Thermostat In the truck, will run fine and trans, with a much bigger cooler, cannot overheat. Overheat is Anything over 200. Transmissions COOK when over 200.

The '04 transmission is an upgrade to previous 4L80E transmissions, and a very good trans, but lack of service and fluid changes can eventually cause problems.