Thread: I am stumped: Honda cooling system issue.

1993 Civic with the 1.5. Came home the other day and the fluid in the coolant overflow was boiling and the fan was not on. Unclipping the coolant temp sensor wire and putting a paper clip in it turned the fan on (no a/c, so I cannot test the fan via the a/c switch), so the fan and relay are fine. I was already going to replace the radiator because it was looking sketchy, so I put a new radiator, coolant fan switch, and thermostat in, along with new coolant. Just took it for a test drive and it is doing the same thing. I once again paper clipped the fan switch wire and the fan turned on just fine.

What now? Besides the ECU, what else turns on the fan? With the temps already in the 90's in Sac, driving around with the heater on is going to a great way to lose weight. Anybody have any ideas?

Thanks.

Edit: Coolant temp sensor? Maybe?

coolant temp sensor sounds faulty.everything except water pump.coolant temp sensor will make you over heat and burn more gas

if radiator is sketchy, the corrossion inside, has potentially clogged your heater core ? have you tested it ? Did you bleed coolant properly ? Have you tried cylinder leak down to test for blown head gasket ? Last thing left would simply be that fan does not pull enough air.

Sounds like a coolant temp switch.

Thanks all, one coolant temp switch coming up. What's the point of the cooling fan switch then if the coolant temp switch tells the ECU when it is too hot and then the ECU turns on the fan? If this doesn't work, I'll start going down the road Nismo_star suggests, or just ditch the car.

Coolant temp switch is in and while I was idling it in the garage, I noticed it was starting to bubble out of the top of the radiator (no cap on while I waited to top it off). So all of these new parts and no change in the action as the fan once again did not turn on. The top radiator hose was really hot, but the lower hose was just warm, I could definitely comfortably hold my hand on it. Does that mean that there is circulation issues? Could the water pump be bad but the belts are still working fine?

Edit: I just need the car to make it another couple of months. I am seriously thinking of pulling off the fan switch connector, putting a wire in it to complete the circuit to turn the fans on, and then sealing it with electrical tape like that, unplugged. The fans would turn on once the key hit ACC, and remain on the rest of the drive, but with the heat out here right now I don't think being too cool will be a problem. Would this be OK or would I be asking for another issue? Or is this putting a band aid on a larger, big problem?

Just took it for a test drive with the radiator fan constantly on. After 10 minutes the car started to buck a bit so I got off the interstate and noticed that once again the coolant in the overflow was boiling.

Could some of this be due to me not burping the system well enough? There was quite a bit of air coming out of the bleed valve. Or are the blades on the water pump degraded enough that they are no longer really pushing water through the system?

bye bye head gasket or dead water pump ?

Just confirmed that there is exhaust in the coolant from a block test. I am going to try that headgasket sealant you pour in the radiator, see if that can limp me through to July. Thanks for all of the help in trying to figure this out!

waterpump