Car is overheating after short drive (3/4 hour) had thermostat changed, put new coolant in radiator. radiator was pressure tested no leaks? car ok short drive to store. resevoir seems always overfilled & radiator seems low?

Hi, No you did not break anything. It just happened by coinsident.
You need to replace the thermostat and put new fluid in. Not just water. If it happens again do a radiator flush and check if fan is working properly. Good luck.

at first,try to add coolant slowly to the radiator not to the reservoir,then start the car ,keep adding coolant on it ,until it is very full.u should see the radiator fan should be also running ,then that is the right tempature.drive a little bit & observe the tempature is the normal or not."""but if u have a coolang pressure tester""",u should do a pressure test & see any leak.it might somewhere in cooling sytem leak.hope it wasn't too late,it might cause head gasket burn,it will turn out a big job.

Overheating can be "boiled" down to a few issues:
*blockage: Something is stopping or slowing the flow. Main suspect is the thermostat. It is designed to open and close at the proper temperature so as to keep the engine at the optimum temperature range. They have a tendency to lock closed and cause overheating. Sometimes it's random. The blockage may be something like sludge or rust in the radiator or gunk that someone put in that does not agree with it.

*coolant/water loss. A leak somewhere. Blown head gasket, cracked head/block, hose, etc.
*pressure loss. This happens when the water gets to boiling temperature but is kept under control by pressure (pressure resists heat) and then something such as the radiator cap releases the pressure and the temperature rises. The coolant will also leak out and then the overheating will be due coolant loss as well. This is especially true with the Cadillac Northstar. The head bolts allow the head to lift off the block, ever so slightly, and pressurize the coolant system with exhaust gases beyond radiator cap pressure limits. It's usually when you accelerate or put the engine under load such as going up hill.

^check for exhaust gases in the coolant. smell it or buy a kit to test.
^get a new thermostat, or, test the old one by boiling it in water on the stove; see if it opens. I always get the "failsafe" kind: fails in the open position.
^check for oil in the coolant or coolant in the oil: grey sludge.
^check for leaks on the ground.
^test the radiator cap. some part stores have a way to test them.
^check to see if it's made by Cadillac. look for the word Northstar. If so, hold on to your wallet. There's a whole new world of overheating adventures.

Ihave a 2000 Dodge Durango i have put a new radiator and the gaskets came back good um i replaced the coolen fan also the thermostate and tested it it it came back good when i run it its fine but when i am in line its hot when i drive it cools down........

bubbling into the overflow may mean a head gasket is gone, it may also mean the radiator or thermostat is blocked. or there is a leak
Clean and flush radiator, check the radiator fins for corrosion
pressure test coolant system
(if this is ok then)
new thermostat
new coolant

Overheating can be the result of several things including: No coolant, stuck thermostat, cracked head, blown head gasket, bad water pump, cracked radiator side tanks, and poin holes in one or more hoses.

Start with the easiest things first. Check coolant level, if it's low you need to find out why. If it's at a normal level you know the coolant is not circulating through the motor. To test this run the car to temperature then feel the upper radiator hose, it should be hot and firm to the touch. Next feel the lower radiator hose it to should be hot and firm to the touch. If it's not the coolant isn't flowing through the motor which is the result of a stuck thermostat.

If the thermostat checks out ok crawl under the car and check all the connections between hoses/motor/radiator. Look at the side tanks of the radiator. If there's a carack in one they will only leak while the system is under pressure. Next check to make sure the water pump is circulating the coolant and not leaking. A siezed water pump will usually stop the pulley from turning resulting in a broken belt.

NExt look around the area of the head gaskets for signs of leakage, again this will only leak while the system is under pressure. Check the oil, if it looks milky there's coolant in it which is a sure sign of a gasket failure or cracked head. Good luck.

Many things can cause this problem.
1. Bad water pump

2.Bad thermostat

3. Clogged up radiator.

4. Coolant system not staying pressurized. Head gasket or coolant leaks

Best to have an auto shop look at it to give a proper diagnoses of the source of the problem.

take fan belt off so water pump does not turn. take thermostat housing off. make sure water level is close to top of thermostat housing (inside) start it, look for air bubbles... If you get them it is due to leaking headgasket, this will be the cause of your overheating and I suspect it's pushing water out too... Just a guess with the limited details.

Did you put a new thermostat in, and did you flush the radiator when you changed the coolant? If not best do that, thermostat might be stuck closed or radiator could have sediment build up and its not cooling the coolant properly. It also could have a bad waterpump and its not pumping the coolant thru the system. If after all that, and it don't fix the overheating problem than i am afraid the problem is internal like head gasget or maybe cracked head.

there is a coolant cap on the overflow bottle check it for seal
i'd just replace it
also if you put the new thermostat in backward the overheating would be significant