Have a 1998 model year Saturn SL2. The coolant boils in Stop and Go traffic. This past summer had the coolant flushed and Coolant Pump Replaced but that did not solve the problem. I am seeing that if I turn the heat on, the engine cools down.
You need to make sure the radiator fan is working. It’s usually an electric fan switched by a thermal switch. So either the fan itself or the switch is not working and you aren’t getting enough airflow while the car is not moving fast enough.
Define “boils”. Are you saying that the coolant in your recovery/overflow tank is actually bubbling? If so then you should have the car evaluated for a head gasket breach. The bubbling may very well be combustion gases blowing through the cooling system. This would also be related to overheating.
Or did you mean “boils” as a figure of speech - as in your temp gauge shows hot? If so then I’d follow rripstop’s suggestion about the fan. If its making it to the red stop driving until its sorted out or it can cost you a lot more than it would otherwise.
If the problem is an engine that is overheating, first and foremost you should check the coolant level to make sure there is sufficient coolant for everything to work properly. Also check the thermostat.
If both the coolant level and the thermostat are both good, then the problem most likely involves the electric fan that is supposed to draw air through the radiator. “rripstop” mentioned the fan and the switch, but there are several other components that could affect the operation of the fan.
If your car has air conditioning, does the fan turn on when you engage the A/C? If not, then check the fuse and/or the fan relay. Also check the ground for the fan itself.
If the fan operates normally with the A/C on but not when you are idling in traffic, then the coolant temperature sending unit is suspect. There are two sensors in this car. One goes directly to the dash gauge, while the other is connected to the PCM (Powertrain Control Module). The one that goes to the PCM is also called the ECT sensor, for Engine Coolant Temperature Sensor. If that sensor is defective and does not read properly, then the PCM doesn’t know to tell the fan to kick on. I think you will find it on the driver’s side of the cylinder head, under the radiator hose. (It is also possible that the PCM itself has gone bad.)
Don’t forget to reset the PCM after changing the ECT sensor.
Was the radiator cap replaced? A cap that won’t hold pressure can cause these symptoms.
These era Saturns are known to have issues with the ECT sensor. A sensor that was made to sit in the coolant stream was made with a plastic housing, which eventually melts. I’m leaning with SongFrog on this one.