Will a faulty thermostat stall my 2001 montero? its temp gets high but i know i have water on it. or would a faulty aux fan be the cause? please help. i dont think i blew up the head gasket.....YET. oil in dipstick is still OIL. no leaks whatsover visible yet my engine stalls interminently.

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First thing to check when the engine is cold is that if there is enough antifreeze in the radiator and after you run the engine for about 5/10 minuter check both the rad hoses to see if they are both at the same temperature, if the return hose which is the bottom one is cold then replace the thermostat. If both hoses are hot or same temp then make sure the radiator fan comes on?

if your sure the cooling system is full than i wouldn't be surprised if you had a head gasket that has failed.

This would explain the water noise, and overheating.

With the engine cold remove the radiator cap, start the vehicle and let it idle. continue to monitor the coolant level in the radiator. top it off if it gets low. If you see a constant perculation of air bubbles coming out of the radiator than the head gasket is bad.

Sometimes you can also smell the radiator or the overflow. If it smells like exhaust than the head gasket is leaking.

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Hi there,

Unfortunately, there is no overheat prevention as such....

What usually happens when an engine gets abnormally hot, is a condition called "Vapor Lock". This means the gas 'boils' before it can reach the combustion chamber and is triggered by an extremely hot engine.

When gas boils, air bubbles form in the fuel, causing the air/fuel mixture to be "too lean" (ie too much air & not enough gas). Consequently, causing the engine to stall. When Vapor Lock occurs, all you can do is wait until the engine cools to an acceptable temperature, so the engine can start.

So, the BIGGEST concern here is.....Why is your engine overheating?

Firstly, you should have the codes read from your vehicle's OBDII computer.. then address which circuits/components need attention.

Secondly, you need to check the following cooling systems components:

- Radiator cap (is it sealing correctly?)
- Coolant (do you have at least 50% coolant mixed with water? Coolant has a high boiling point)
- Thermostat (is it allowing coolant to reach the engine?)
- Coolant Temp Sensor (your computer relies on correct data from this sensor)
- Hoses (make sure none of them have collapsed or soft)
- Radiator (ensure passage are not blocked)
- Water pump (check operation and/or leaks)

You would be best to have your cooling system "pressure tested" - this will identify any fluid or air leaks in the system.

Good luck...


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if you have high miles, 75k or more I would go ahead and have tempature sensor and thermostat it self change. I don't see battery cable would have any bearing to the temperature guage or cooling process. Both switch work almost the same, at time it work well other time it read or work incorrectly because it a sign of unit becoming faulty. If the temperature sensor is faulty half of the time it well give you incorrect reading however if the temp sensor working properly and the Thermostat is not, you will also get a high temp reading due to the Thermostat is not working properly allowing the hot antifreeze to flow out from the engine to the radiator which cause the hot antifreeze to be remain lock up in the engine block. Thermostat suppose to open and close when it reach its temperature; at the same time I would also replace thermostat switch which operate the cooling fan. all three tend to go bad over times; replacing all three is a great ideas. Thermostat, thermostat switch and temperature sensor.

When the engine overheats, steam moves to the reserve tank to relieve pressure in the system, and can seem like it is overflowing.

Civic cooling systems always require an auxilliary fan or blower. Have this checked for serviceability. If the aux.fan is working properly, this points to other problems with your cooling system, which may include faulty hoses, water pump failure, and/or water temp. sensor failure.

Hope this helps.

check the lower radiator hose it may be collapsing at high engine speed

sounds like a faulty sender unit not passing the right voltage which is causing the gauge to read high

if you replaced the relay because it melted that means there was a short in that circuit. if the water pump is circulating the coolant properly then there is either a faulty temp sending unit on the intake manifold. a faulty sensor on the fan itself, or there is a blockage in the system. if all of these are ok then that means that you have a air bubble in the system. to correct this start the engine with the radiator cap off turn your heater on to high fan high heat and run the system. when the engine reaches temp the upper radiator hose should get real hot ,if it doesn't then the thermostat did not open. replace the thermostat. if it gets hot then let the engine run for a bit top off the coolant shut vehicle down and replace radiator cap this should solve the problem

your thermostat is either no good or is stuck.replace it.and now you need to check the sides of the radiator(tubes) for a crack.