2000 Sunfire coolant problem. Engine overheating, changed water pump, thermostat, put new head gasket, checked head, no warp. Started car, went to temperature, blows water out of reservoir. Checked compression 150 psi per cylinder. Filled radiator, left overnight, no drop in water.

Sounds like the thermostat is stuck shut.

maybe you have a blown head gasket your leaking head gasket when ur car is cold open your radiator cap see if the coolant in it try to tap up coolant until the neck of your radiator then start your engine and observe the radiator neck if the collant puks it out if your coolant is pukking out meaning you have a leak or blown head gasket and thats the cuz of your overheating

I shouldn't be blocked because it is pretty new. The systems are usually good for 10 yrs or so before they start getting gunked up. I would think it is either the electric fan or the fan clutch (whichever you have) could be out and it isn't cooling the engine. Also, you could have air in the system which could cause the rest of the coolant to not circulate. Check for an air bleeder valve near the top of the engine, usually near the thermostat housing.

I don't see any mention of having the cooling system flushed or the water pump being serviced. Both could be creating your problem. Also are you sure the new head gasket was installed properly, the right one and not upside down.

Head gaskets leaking. Are you low on antifreeze? Does your engine oil have moisture on the dipstick when you pill the stick out.

If the engine has overheated, chances are pretty good that you now have a warped or cracked cylinder head and a blown head gasket. Those engines are very unforgiving when it comes to being overheated.

It sounds like you have a partial blockage in the cooling system. If liquid gasket material was used with the pump an or thermostat replacement some of this material may be in the coolant path. Other things to consider; your thermostat is the wrong temperature, you got a bad water pump. Take the radiator off and start the car when it is cold. Let it idle and watch to see if coolant begins to circulate after the engine reaches the operating temperature to be sure the thermostat is working correctly as well as the pump.

YOU COULD HAVE A DEFECTIVE WATER PUMP OR THERMOSTAT ALSO RADIATOR PRESSURE CAP.MAKE SURE YOUR WATER PUMP IS BEING TURNED BY DRIVE BELT.NOT SLIPPING.MAKE SURE COOLANT SYSTEM HAS BEEN BLED AND YOU HAVE HALF ANTIFREEZE HALF WATER.CHECK YOUR CRANKCASE WHEN CAR COOLS DOWN.IF OIL STILL LOOK LIKE MILK SHAKE.YOUR NEW HEAD GASKETS LEAKING.THE MECHANIC WHO REPLACED HEAD GASKET DIDNT DECK THE HEADS.THEY PROBABLY NEED SHAVED A LITTLE SO HEAD GASKET WILL SEAL.

looks like you have done everything but the problem with your car is that the cylider head gasket has gone have a look at the dipstick or remove the oil filler cap if it looks like mayo then 100% head gasket has failed you said no water on the floor so it must have gone into engine only way this can happen is head gasket failing, if you have put lot of water in to the cooling system then your sump will be full of oil water mix.

let us know your findings so we can help you more if you need it

Hi,
If the car is overheating it could be due to a thermostat which is stuck in the closed position, a failed water pump or just a slack belt driving it. I think there will be a "little" tube carrying coolant from the engine to the coolant expansion tank, and if you run the engine with the filler cap removed you should see water coming through that pipe IF the rump is running. A failed water pump will not necessarily leak, it just won't pump the water round the engine.

Always take care when dealing with a pressurised cooling system on an overheating engine - the water may well be above boiling point.

If you run the engine without coolant the cylinder head may well warp and repair bill will be huge.

Hope this helps you a bit. D