2005 gmc envoy overheating when engine shut off

What engine was doing before you change the thermostat?

There may be a slight head gasket leak to the coolant jacket, not large enough to overheat the engine. It is normal for some coolant to escape at operating temp, but not lots, and it should cool down to about the recommended level again.

Something is pressurising the coolant jacket. Have it tested for the presence of combustion gasses in the coolant. This is a simple test.

Another thing, that model often develops a crack in the radiator plastic top tank. It is not the problem here, but worth knowing.

https://www.youtube.com/watch?v=a3J00_e7fyo

If your Jeep is overheating and the coolant reservoir is bubbling, it could indicate that there is an issue with the cooling system. Here are a few possible causes:

1. The radiator cap is faulty: The radiator cap is responsible for maintaining the proper pressure in the cooling system. If it is not functioning properly, it could cause the coolant to boil and create bubbles in the reservoir.
2. The water pump is not working: The water pump circulates the coolant throughout the engine. If it is not working properly, the coolant may not be circulating as it should, which could cause the engine to overheat.
3. The thermostat is stuck: The thermostat is responsible for regulating the flow of coolant into the engine. If it is stuck in the closed position, it could restrict the flow of coolant and cause the engine to overheat.
4. There is a leak in the cooling system: If there is a leak in the cooling system, the coolant level in the reservoir may be low, which could cause the engine to overheat.

It is important to address any issues with the cooling system as soon as possible, as an overheating engine can cause serious damage. You may want to take your Jeep to a mechanic for further diagnosis and repair.

You have air trapped in system , change thermostat , bleed air from system , let it run hot while adding coolant with blower full blast on all front and rear heaters .

Usually the vapor canister - worse when the weather is very hot.
May or may not be normal.
Is the check engine light on ?

Hi Odnanref, If the coolant is boiling you have a problem with the cooling system. If you cannot see a leakage have the thermostat in the engine checked and replaced and hope that you have not overheated the engine to the extent of needing a cylinder head reconditioning job carried out. The AC is effected because the condenser is mounted in front of the radiator and depends on cooling from the fan. If the engine overheats the AC will be unable to cool. Regards John

I have a '05 Envoy, 65k miles.
The engine randomly turns off. At a stop light, while making a turn.
There are no check engine lights on.
Starts right back up. Major pain at intersections.

Try www.manualowl.com

The three most likely thing's cause overheating are faulty thermostat,electric fan or clogged radiator. Only at has been overheat so much it boils dry that it will cause engine trouble. Most common problem's are blown cylinder head gasket or a cracked cylinder head.
mixing coolant and water depends on where the gasket has blown or head is cracked. You will first need to check if it actually is overheating. The reason is. If the head is cracked or gasket blown then you can get a false boiling which is compresion from the cylinders blows through the crack in the head or gasket causing the coolant to blow out of the radiator cap.Fill the radiator to the top leave the cap off then start the engine.If the water blows out then you will need to remove the cylinder head check the gasket is ok. If its damaged replace if not get the head checked for crack's. If no water blow's when you start it check the thermostat is working properly. To check the thermostat put it a in a saucepan cover it with water bring the water to the boil. It should open before the water boil's but near boiling-point. If its ok then start the engine again leave it running until it boils and check the fan is running. If that's ok then its radiator problem. Their is no way to check if the radiator is ok you will need to get a new one. One last point. If the cylinder head or gasket are faulty it was caused by overheating so by just fixing the cylinder head problem is not a cure it will overheat again. Check the three things I mentioned at the begining and told you how to check them. Hope this help's. Cheer's

when does it do this? If it does it right after you shut it off, then its supposed to do that, as your engine will actually get hotter, before it cools down.