Had radiator flushed and coolant added 4 months ago. yesterday coolant needed light flashed on and then it went off. reservoir was empty. added water to reservoir, cranked the car and let it run 5 mins. no leakage from reservoir. what's going on? please help!! I own a 2000 Buick Regal.

Maybe it's not over heating , the gauge is bad .
Coolant not emptying from the reservoir to the radiator until the car turns off. That's how it works , doesn't draw coolant while vehicle is running . System under pressure , too high of pressure an it sends coolant to the reservoir, when you shut the vehicle off as it cools down it draws coolant back into the radiator. Your best bet , take it to a qualified GM technician . The man who knows your vehicle best .

The way to tell if something is wrong check oil cap. Look for a white foam sometimes it's brown showing coolant in oil also look for white or blue smoke coming out of tailpipe. If you don't see any of these simple drain reservoir and flush it. I would also drain radiator to be on safe side. It is possible that last owner put oil in reservoir I have seen strange things like that and worse

Start with a "professional" coolant system flush. Sounds like there's a blockage somewhere. If you're putting coolant in the resevoir and not directly in the radiator, and it's disapearing, check the radiator. If radiator is full it's a blockage, if it's low/empty there's a leak.

Was the water added to the coolant reservoir or into the radiator? If the coolant reservoir it's a simple matter to unbolt it, drain it, reinstall and refill to proper level. If water was added to the radiator, it's best to drain the coolingg system and refill with the proper 50/50 mix of Dexcool. Water in the radiator will not hurt anything in the short term, but will not provide adequate protection.

Step 1:

When the thermo..do not work,there is an easy way to know...let the car running for at least 10min..turn it off..touch upper and lower hoses...if any of them is hot and the other is cold...thermos..not working.

Step 2:

check if fans activate when it reaches normal temperature, if they dont,replace fan switch at the botton of radiator,or check if the fans are burned.

Step 3:

you can flush the radiator by the usual way,but it will not unclog any cell of radiator...you must send it for service... but before u do it..do the cheap and easy staff...by the way...that car operate with a different cooling system...thats a closed pressured...so changing the cap of the reservoir helps ...since it has some valves that goes broken when is not change...hope it helps...

May be the water pump,

Well i suggest to never use stop leak because it will clog up cooling ports not only in the radiator but the engine also. I would flush the whole system you can purchase a flush kit at a local parts store. it is usually a cleaner that you run threw the system let the engine get up to temp for a while then drain everything after it cools down and take the thermostat out of the system usually i will leave the hose disconnected at the thermostat instead and stick a water hose in the radiator turn on and let it flush sometimes you have to start your vehicle but make sure you don't over heat it. If you can tell that there is a crack in the radiator i would replace it stop leak in my line of work is a no no it causes more issues that solves. If you have any more questions pleas let me know and leave good feedback please.

is the coolant level low when it comes on, due you have to keep adding coolant to the surge tank, have you repalced the surge tank cap?

need to perform a coolant pressure test. fill the reservoir and after the engine cools down fill the radiator, next start the engine and wait till the coolant system builds pressure then turn off the engine and using a mirror and flash light look for a leak.check water pump, hoses,radiator tanks for cracks,intake gasket at the corners espesically at the back next to the trans.also pull the carpet back and check for coolant leaking from the heater core,and last remove the sparkplugs and check for leaking head gaskets.hope this helped.

From your description of symtoms it sounds like you have a bad water pump. If the coolant is not circulating properly you will have a heating problem. Sometimes even a new thermostat can stick and cause the engine to overheat. I have seen them fail in as little as a week after they were installed.