2008 Edge gurgling, overheats but then okay
 

Alright trivia problem here, please help. My 2008 Edge overheated, was very low on fluid in radiator. We added water. It overheats when driving. I turn it off, it cools down and water sounds gurgle. If I turn on the heater, it blows cold, but then warm and car will cool down. Drive a little ways, it overheats again. So I am thinking maybe thermostat stuck and water pump is bad, or did heater core go out? What ways can I tell?

Please give me solid ideas and opinions.

Thanks

Could be the thermostat, could be the water pump a couple more could be s .
You can remove the thermostat and test it in a pan of boiling water, but if you are going to go through all that trouble , just replace it.
I am concerned about just how hot the engine got, because that can cause warped heads burned valves etc.
You might just remove the thermostat , refill the engine and see what you get.
There are various tools that can help pin down the culprit like a laser temp gun, which not everyone has. So it's trial and error.
If the coolant level has not gone down any, still could be a head gasket problem

Pressure test the cooling system and check for leaks. The coolant went somewhere. If you are just adding water, it will boil at 212 degrees.Not hard to do in this heat.You need to add a coolant to raise the boiling point. Connect a scan tool to see what temperature is the computer seeing. Dash gauges cannot be relied on. Under what conditions is it overheating? On the highway usually means a water flow problem from restricted water tubes in the radiator. During stop and go driving, usually is an air flow issue. Fan not working or plug fins on the radiator or a/c condensor. I doubt it is a water pump unless it is leaking. It is extremely rare to find a water pump impellor come loose on its shaft and not circulate coolant. I never seen one yet.Thermostat is possible and cheap. It is worth a try. I doubt it is a head gasket. When head gaskets are bad enough to cause over heating, heavy smelly smoke will come out the tail pipe or high pressure combustion gases will enter the cooling system, forcing coolant out the expansion bottle.