I have a 90 Buick Regal Gran Sport which runs great except it overheats in stop and go traffic. The thermostat is working, the radiator has flow, the fans are on, but the temp gauge keeps climbing. Do you know whether the fans are 2 speed? They spin but kind of calmly. If there is a high speed, what controls that?

Fan speeds are high and low and are contolled by relays. The PCM commands what speed to run the fan at by supplying a ground to the desired relay based off vehicle speed and/or coolant temperature. The fact that your fan is coming on might be a good sign.

Drive the car for a few minutes to establish normal operating temperatures (about 5-10 minutes maybe)
With a non contact thermometer, or your hand, check to see that your radiator is consistant temp from top to bottom. While your flow rate may be good, you may be using only a portion of your cooling capacity due to blockage in a portion of those veins.
Check to see that there isnt any debris in the front of the condensor or between the radiator and the condensor.

Climbing temperature gauge may not be overheating on hotter days/AC running, unless it constantly climbs and you KNOW its going to peak in the red zone.

Thanks for the reply. There are only two wires to each fan. When "on", there is 12V and ground on those wires. How can a pair of relays cause two speeds? I would like this to be true, I just don't see how that is possible.

mine was doing the same thing...just flushed the whole sys out really really good now it runs cool all times.

Thanks for the reply. There are only two wires to each fan. When "on", there is 12V and ground on those wires. How can a pair of relays cause two speeds? I would like this to be true, I just don't see how that is possible.

The main cooling fan on my buick has a ballast resistor at the bottom. When the fan is command in low speed, power from the low speed relay applies 12v to one side of that resistor. The current reduction from the resistor runs the fan on low. When the PCM commands the high speed relay on, 12v is supplied to the other side of the resistor bypassing it entirely and completing the circuit to the cooling fan.

The secondary cooling fan is commanded by the AC request/AC pressure switch and under normal operating conditions only runs when the AC clutch is engaged.