Flushing the radiator may help with the cooling problem but not necessarily make the engine run smoother. If it is a 6 cyliner engine check for a possible leaking lower intake manifold gasket. If the LIM gasket is bad, it may be leaking coolant into the oil and possibly into the cylinders. Also it may leak externally or it may leak internally. Go to http://www.gaoc.com for more info on this problem. If this is the case, it is a serious problem and you shouldn't drive the car until you get it fixed. I have owned these cars in one form or another since 1994 and the radiator leaves a lot to be desired. The radiator seems to clog very easily. So it requires a lot more maintenance that GM likes to admit. I have never had a problem with the thermostats and only had one water pump failure. I also have never had a problem with the fan but, like others have said, they should be checked as well GOOD LUCK!! Sometimes having the radiator flushed will help; however, it may be your themostat is sticking causing the motor to run hot. If this is the case, you should get a new themostat installed. Also check that the fan is running with the engine hot and in idle. The fans wear out may need replacement. It may also be the fan control circuit. I had that problem! Make sure your radiator cap is not missing the seal! Without the seal pressure is not kept in which will cause the engine to overheat! Simple problem, cheap fix!
Your truck is overheating because it needs a new radiator. I had the same problem, after I installed the new radiator and flushed out my remaining cooling system I never had a overheating problem since.
Either the water pump impeller is loose on it's shaft, or you have a leaking head gasket.
The radiator on a 1999 Pontiac Grand Prix is flushed by draining the coolant, filling the system with water, adding a liquid flush to the system, and running it for a few minutes. The system is then drained, flushed with fresh water, and refilled with coolant.
Check the water pump
Engine overheating is a good indicator. Some people get them flushed regularly as part of regular maintenance.
Bad thermostat maybe?
Water pump defective.
The radiator may have debris that needs to be flushed out.
you must be a wierdo.stupid.
Low coolant? System air bound? Hoses collapsing under pressure? Water pump not circulating coolant?
you need to have it flushed
sounds like you have a cracked head or cracked block.however, i would check to make sure it is not transmission oil and thereby ruling out a radiator problem