1999 buick centry overheating overflowing the overflow

You have a failed IAC (Idle air control valve) its on the throttle body,

crack or hole in overflow container

i would check the thermostat first. even if your mechanic did replace it.the thermostats you buy these days only last about a year or 2.

Assuming the engine is ok, no leaking head gasket or exhaust problem, you need to know if the radiator fan comes on when the engine reaches 225 degrees. It should also come on when you turn the ac on if the ac works.
Its also possible you have air in the cooling system.

Trust you mech on this one.

I assume you have a 3.8L V6. Probably thermostat, but first take a look in the radiator to make sure it is full. Not just the plastic overflow tank, take the radiator cap off and look. Make sure the engine is cold though. The radiator should be full to the top. The way the system works is that as you drive your car, the water heats up and expands and the check valve in the radiator cap will let the overflow go into the plastic tank when the pressure get over a set amount usually 14-17 lbs. When you shut off your engine, the water will be slowly sucked back into the radiator as the engine cools. if the radiator cap is bad, it may not let the water get sucked back into the radiator and the engine will run hot, you will get air and steam bubbles in the engine, the thermostat will work as long as it has water running by it but if a slug of steam goes by it, it will close. "Burping" that engine is a pain but just keep the overflow tank full and check it every time you *start* the car. The air will work itself out.

Visit gmownercenter_buick (1993-present. Must have a Yahoo ID to log in.) for acces to the Owners Manual.

Good luck (remember rated this help).

If it's overflowing.... I doubt it was just sitting for two hours. Overflowing is because of overheating or a blockage, which only affect the car when it's running. It is not overflowing, but simply leaking, then you have a leak. Pressure test the system, replace what's leaking, and, depending on the coolant condition, top up or flush it.

I suspect this vehicle has been overheated, because you asked about the lights for engine/coolant temperature, and because you said "overflowing". If this is the case, do the same thing as if it were a leak, but have a technician check the cylinder head for fractures and warping as well.

Next time pay attention to the temperature gauge and don't wait for the "idiot light" to come on on the dash. A slightly high gauge is a problem, but an engine/coolant temperature light is usually an expensive problem.

have u bled the cooling system ?warm the car and cut the car off right before the fans come on ,let sit for 30-35 minutes,see if the coolant drops in res. if so repeat process untill coolant stops droping ,then drive car regularly if overheating stops ,but monitor it because it will drop somemore/there has been reports of new and rebuilt water pumps nt having correct propelar mounted on them/ backwards etc. if this helps let me know [email protected]

I had trouble with overheating on my 2000 Grand Am, The dealer could not even resolve the issue,(they wanted to replace the intake gaskets)...I knew that was not the issue, no air leaks or water leaking there; so I sit down to think; what are the causes of overheating. Thermostat sticking - nope not it, water circulates, Water leak - nope not it, has water stays until it gets too hot and goes out overflow, fans working - yep...hummmm the only other thing I could think of was losing of water pressure, yep that's it - the cap on the coolant tank was going bad, got a new cap ($8.00) replaced the old one and no more trouble going on 6 months now.

Hope this may solve your issue.