Hey, the temperature in my 98 Honda Civic was going up and down so I replaced the thermostat and changed the coolant. It worked fine for about a week; it would stay at one temperature and the heat was good. Now it is going up and down again. The resovar was above the max fill line when I got home but I wasn’t able to check the radiator, to hot. Any ideas? Thanks.

 

Was the radiator low when you changed the coolant? It sounds to me like you've either got a coolant leak or air trapped in the system.

 

You have to check in the radiator, when cold. The radiator should stay full to the top. Park the car on level ground or facing uphill then wait until it is completely cold before opening the radiator.

One common reason for coolant leaving the radiator and overflowing the reservoir tank is a slow leak in the head gasket.

 

Unplug the radiator fan connector at the thermostat housing. Using a paperclip jump the 2 terminals together. Let us know if the fan comes on.


and did you ENSURE that you have bled the cooling system of air?


The tool in this video can be rented from most auto parts stores for a small fee:

 

 

Time to find the leak then. Best way is with a pressure tester