Okay, here is the deal. I have a 2000 Honda Civic Si. I just recently swapped a OBD2 JDM GSR into the car. Now, everything is hooked up all the lines etc... all fluids are in. The problem I am having is that my car is overheating. The bottom coolant hose into the thermostat is staying cold and the upper hose is warming up. So I figured hmm... must be the thermostat. This morning I went out and bought a new one and replaced that with the gasket and all and then sat their and added coolant and let it warm up and get all the air out of the lines and motor etc. Well... 1st, my fan NEVER kicks on and that bottom hose is staying cold. The water in the radiator gets to boiling point.

So my question is.. what can it be? I have replaced the thermostat and the fan is plugged in and all the lines and plugs are where they should be.

Any help would be great thanks!

 

Try flushing the cooling system/radiator of debris.

Might the water pump have failed?

Regarding the radiator fan, try putting a jumper wire across the wire harness connector for the coolant temperature switch on the thermostat housing. Did you reconnect this connector to the switch after replacing the thermostat?

 

Yea I wouldnt think it would be the water pump because I would think it would be making a weird noise or something. The water gets to boiling point so that's another reason why I wouldnt think it would be that. I did reconnect the connector and its all tight and fine. The only other thing I can think of is MAYBE a relay or I might just try taking the thermostat off and drive around and see what's up with it.

 

Idk if this helps but I just took my old thermostat and put it in water and boiled it and it works fine. So now IDK what because it's preventing that coolant line to heat up for the thermostat to open.

 

Does the car make heat?
Aside of it overheating?

 

No, no heat in the inside of the car. But does boil from the top of the radiator

 

Could be a bad fan relay.

 

Drain the radiator from the lower hose, and then run a garden hose through the radiator. if it trickles out, its probably clogged. I put a used GSR radiator in my EK and it ended up being clogged.

 

Hmm that could be.. i'll try both of those tomorrow first the relay and then if not the relay then i'll drain the radiator. The radiator had sat empty for about 2 months while there was no motor in the car but the cap was on the top and after I had finished draining the coolant when taking the motor out I had closed everything up but i will try again.