Hi all.

The car is a '90 Civic DX hatchback with the 1.5L engine.

The cooling system is having issues that I can't diagnose for the life of me.
Changed the head gasket a month ago. Procedure went well. The car was then overheating due to not enough bleeding of the system, and a fan that didnt turn on. After bleeding, the car would only overheat in slow driving, idling or traffic as the fan didnt work which seems normal. Checked the fan, it worked when the thermoswitch was bypassed. Put in a new thermoswitch, no improvements. Checked the thermoswitch, it activates at 95*C which is whats written on it when put inside some hot water.
But for some reason, once its in the engine it does not activate at all. even though the temperature gauge is reading 3/4 max ( which is above the thermoswitch temp I think) it doesnt activate.
I stop the car when it reaches this 3/4 mark. A thermometer in the radiator cap shows about 85*C at this point, but I'm sure its colder than inside the bloc. An continuity tester on the switch still shows the switch is closed at this point whereas the temp gauge in the car is very slightly under 3/4.

I don't understand why the switch doesnt activate while the engine is clearly hot. Can't keep my hand on the engine coolant return hose for more than a second or two. Without a thermostat in, the overheating issues take much more idling time to happen ( if that can be a clue). Is it possible that while scrapping off the old head gasket, some of the material fell in the cooling circuit and clogged up the water pump or radiator?

Thanks in advance!

 

Also another possible clue is that when i turn on the car, the temperature gauge very rapidly reaches its normal operating temperature even though all parts of the engine are cool the touch. The needle then stays there for some time until the engine actually heats up. Then after some time it will start creeping up. having the cabin heater to max obviously helps the temperature needle go down for some time.

 

To get the fan to work did you just jump the ECT switch plug or supply power directly to the rad fan?

If the fan worked by jumping the plug and it is not working with the new ECT switch, it can only be a defective ECT switch. 94

 

The fan works when bypassing the thermoswitch. I tested the switch in hot water and it works. The one that was in the engine before works as well.

 

Check radiator at operating temp for hot/cold areas due to clogging up. If there is noticeable temp. variation, it's clogged and switch isn't getting hot enough to close.

 

From what i read. U Jump the swith and fan will be on and u test the swith and does work at temp but will overheat at idle but not at speed.

my assumption would thermostat, cuz the water couldn't flow thru so switch never detect the temp so no fan.

 

Had a similar problem with a b16 engine once. Wouldn't engage V-tec for no apparent reason. After buying that engine, I stripped it and found a ton of "stop leak" in the water jackets in the engine block. Clogged the sensors at the bottom end....

My suggestion is: remove the drain plug next to the exhaust manifold, this leaves a rather large hole in the engine block, making it easier to check for debris in the water jackets. If you find any on the front of the engine, chances are there is debris
at the back of the engine where the thermo switch is located.

A not so great solution is to either bridge the wires going to the switch so it runs permanently, or build a switch between the two cables. I know it's not the best route to go, but it might help you out for a while.

Good luck!

 

Pretty sure he might have it fixed already. Thread is from 7 months ago.