2000 Oldsmobile Intrigue Cooling problem

Details: 3.5L V6 north star (i believe) 2000 Oldsmobile Intrigue
When idling / low RPM the car will overheat, when on the highway the temp seems normal/constant there is a little fluctuation if you slow
down and speed up again.
There was/is a small leak in the head gasket that I put some stop leak in (stupid move i now know) but after i put that in the over heating problem started about an hour later i had the system flushed.
The problem still existed and got worse, i replaced the thermostat and it settled down to what i described in the first paragraph.
The fans run and kick up even higher when a temp around 220, i believe, is reached. The pump seems to be working fine because I get plenty of heat in the car. The upper part of the radiator hose is warm and gets hotter when the engine temp goes up and the lower hose is cool.
When at lower speeds the only way that it seem to cool is to rev the engine to about 1800 or 2000 or over then it goes down to a normal operating temperature.
I had a pressure test done and it held.
I also just replaced the radiator to see if it was clogged. It still over heats when RPMs are 1800 - 2000 or below.
Any idea's or things to look at would be appreciated because I'm out of them.
Thanks!
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____****When idling / low RPM the car will overheat, when on the highway the temp seems normal/constant there is a little fluctuation if you slow down and speed up again. There was/is a small leak in the head gasket that I put some stop leak in (stupid move i now know) but after i put that in the over heating problem started about an hour later i had the system flushed. The problem still existed and got worse, i replaced the thermostat and it settled down to what i described in the first paragraph. The fans run and kick up even higher when a temp around 220, i believe, is reached. The pump seems to be working fine because I get plenty of heat in the car. The upper part of the radiator hose is warm and gets hotter when the engine temp goes up and the lower hose is cool. When at lower speeds the only way that it seem to cool is to rev the engine to about 1800 or 2000 or over then it goes down to a normal operating temperature. I had a pressure test done and it held. I also just replaced the radiator to see if it was clogged. It still over heats when RPMs are 1800 - 2000 or below.___*******
Loose drive belt/faulty Water Pump/fan speed problem, according to the symptoms described. Scan for trouble codes and record them, then clear all codes. Since it passed a pressure test leaks can be ruled out. If you are seeing a coolant temp telltale light at low speeds: there has been a known problem with the grounds to the fan motors. Once the cooling system is proven good, then the problem is with the control/computer system.
Hope this helps some.....
Dave S(Texas)
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Divide and conquer.
When you say 'rev' the motor, do you mean the vehicle motionless? If so, then it might be a flow issue and more than likely water pump related. Although it could be a blocked hose. Or it could be an air bubble in the motor.
If you mean the vehicle moving, you have to determine if the air moving through the radiator solves the problem and not the engine revving. Get a box fan or two. Heck, even a leaf blower. Get it to raise temp and just sitting there, see if the internal fan goes on. If not, blow air with your box fan. If the fan didn't go on and the box fan lowered the temp, then it's probably related to the internal fan.
Measure the temp at the radiator. When it heats up, is the radiator getting really hot? MEASURE IT, don't say 'yeah, it's hot'. Does revving the engine make the radiator get hotter?
Also, does turning on the heater in the car lower the temp? If the internal fan is fine and cycling, and 'moving' the vehicle cools it down, does turning on the heater and blowing hot air help? Maybe the radiator just has clogged fins. Does the vehicle run fine on the highway and when you come off the highway does the temp suddenly shoot skyward as you sit at a light? Even if you 'rev' the engine? Is the radiator hot?
There's multiple issues here. One is getting the heat from the engine into the water. That's tough to check. You might have an air bubble or blockage. The other is moving hot water to the radiator. MEASURE IT! Make sure the heat is getting to where it CAN be blown off to the air. Finally, getting the heat from the water to the air. Measure the temp of the radiator right where the hoses attach, so you know the temp in and the temp out, then you can figure out where to further attack the problem. If the temp in is close to the temp out, then you should look at a radiator/fan issue.
Mike

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