Ok, I have a 1997 Olds Bravada that is overheating. It will idle with the AC on and not overheat. On the highway or in town driving with AC on, it overheats. AC off, it does not.

AC was recently fixed so it would work again. Since then, lots of cooling issues. This was a recent purchase, so don't know much about the maintenance history.

Truck overheated a few days ago (was not run dry, son pulled over in good time). After examining the coolant, it was VERY dirty. so we drained the system and flushed it out with a hose. Both directions through the radiator, too. since the system was open, replace the thermostat and radiator cap. Cheap to do and puts in in a known state with those pieces. Tested the thermostat and it did not seem to open. Thought I had the problem knocked. yesterday, I notice a puddle under the truck after driving it some during the day. turns out the water pump was leaking. Replaced that this morning and went for a drive. Still overheated. The fan clutch seemed weak, so I replaced that and with a hose ran water through the back and front sides of the radiator and AC evaporator.

Still overheated.

I am wondering now if I could have a some what plugged up radiator causing low flow. It is the only piece I have not changed, but decided to ask some opinions here first.

Oil looks good, no milk or foam. No leaks in coolant system that I can find either.

I live in Kansas City area and it is HOT out, but the truck should be able to handle it.

thanks for any thoughts...

 

Also, on last drive after replacing the fan clutch, temp got to a little over 210 and was climbing. shut off AC, temp held at just above 210. Turned on heater and high fan, and engine cooled back down slowly.

 

Radiator? - Good probability.

Check first for obstruction and dirt outside. Look for bent fins.
Sometimes when replacing stuff people tend to move along the radiator up and down. When you bend the small aluminium fins it obstructs airflow.
Had a radiator once causing an overheat condition. My girl could drive it home with the heating on and on full blast... AZ spring time. Guess - she was mad.

At home straightened all the fins which were bent downwards because some jerk had pushed down with both hands to fix the belt when servicing the car - mind you a pro garage.
An area of about two times 2 x 8 inches had been bent. Caused an overheat

Flushing the radiator is also a good idea. If the car ran without proper antifreeze it may have accumulated a lot of rust debris which sometimes settles in the lower part of the radiator and clogs up a part of it.

When the A/C is on the A/C radiator which is located in front of the coolant radiator will heat up this portion reducing the cooling surface.