strange overheating problem

[kcs213]

At hwy speeds car overheats but when stopped and at idle car cools down to normal. As soon as I stop the car and open the hood I do not see the coolant boiling and when I touch the hoses they are hot but not super hot like I would think. The car got a new water pump and radiator last fall and there was not problems all winter then in the spring this all of a sudden started. so far our shop mechanic as replaced the water pump, hoses, thermostat, coolant temp sensor, fan clutch, and has tried two different types of fluid. Now we have it at a different shop and they have replace the fan clutch twice and say they have to put on two electric fans because the other one is not pulling enough air through the radiator. They took it for a ride and when it started to overheat they turned on the heater and it started to cool down so that is why they say we need to electric fans. I may not be the smartest but at hwy speeds plenty of air is going through the radiator so two electric fans is not going to fix it. It is a 2004 Cadillac escalade 6.0 motor converted to limousine. Here are my thoughts as they will not listen to me but maybe they will listen to you. Being it is a limo when the water pump was replace last fall they put on a smaller one and there is a bigger one that is made for limos to have better water flow. Or there is some type of valve or even electric valve that is blocking the water from flowing through the radiator. Or the coolant has a air block and they don't have the system bleed but they told me there is no bleeders screws on the coolant system. there has been hundreds of dollars spent and nothing is working so any help would be appreciated

[Blue Bowtie]

Where the Hell is Neenah? https://www.youtube.com/watch?v=Iqw7D-6W5kQ

Turning on the heater to drop the temperature is a HUGE clue. There is not enough heat transfer is happening at the radiator itself. The water pump is obviously moving enough coolant since the heater will strip off the excess. That wouldn't happen if the coolant flow was inadequate.

Has the AC condenser been pulled away from the front of the radiator to clean out debris? Is the lower air deflector still in place and not broken off? Has the radiator been flushed (chemically)?

FWIW, electric fans are effective, but electric fans shut off at speeds above 40MPH in factory installations, relying solely on ram air. It works just fine if everything is intact.

If you have the guys in Menasha confused, drive it down to Oshkosh. They'll figure it out.