Cooling fan issues

[Aaronams25]

So I'm having issues with my cooling fans only kicking on after I have ran the car for quite some time in stop and go traffic at high RPM and only after I turn the car off and take the key out of the ignition. this is mainly when the coolant is flowing out of the reservoir tank.

Brand new items include: Thermostat opens at 170F. Thermostat fan switch Unknown temp for for this one. Secondary fan switch closes circuit at 188F (on) opens circuit at 166F (off).

The temp gauge sender unit is not new but functions properly. The ground wire is secured to the thermostat housing.

If I jump the plugs one the fan switches the fans will turn on. Each plug works correctly. And because of this I assume the relay works. And I have switched the relay with the seatbelt re-tractor relay. No change there. And the fuses are all good. The wiring is very murky because the loom has been cut for various reason but should be in the clear.

Side notes are that my coolant is mostly water which boils at a lower temp than antifreeze/coolant. It boils expands rises in temp rapidly and needs to excape which explains the overflow and rapid climb in temp. I will drain and replace with 50/50 mix this payday.

If anyone here has further knowledge and a better possibility than the bad mix i have please chime in.

Thank you in advance

[F22Chris]

The harness on the temperature switch on the front water outlet could be bad. It’s been bad in CB’s I’ve owned. I had to zip tie them in awkward angles to get any contact. Wiggle that connector at operating temperature & see if the fans come on. Just because it works when jumped doesn’t mean it’s contacting the switch, you know?

You can buy a new one from summit if need be:

https://www.summitracing.com/parts/r...RoCumAQAvD_BwE

[Aaronams25]

I will try this however, If I jump the two terminals on the same plug and it turns on the fans. that tells me that the plug should work fine. However I will try to spread the prongs on the switch that go into the plug. Just so it ensures the metal from the switch is making proper contact with the plug. But even still I have multiple plugs lying around the garage. Right now I think my best options are to

1: Change the coolant to a 50/50 mix
2: Install the stock ECU
3: Replace my Relay(working) with a brand new relay(hopefully working) "lol".
4: Replace the ICU(under the dash) with a working one.

I should have this issue fixed this weekend.

But I still encourage everyone to chime in and help to solve this very common Honda issue.

Thank you all in advance.

[F22Chris]

Just because it works when jumped doesn’t mean it’s contacting the switch

I’m willing to put money on this being the problem.

The ECU doesn’t tell the fan to turn on. The fan switch reaches a temperature, closes the circuit, and the fans turn on.

Water actually cools better than antifreeze, it just lacks the ability to lubricate and protect cooling system components.

If your relay is working don’t replace it, it’s not broken. “If it ain’t broke don’t fix it”

If I’m not mistaken (correct me if I’m wrong please) the ICU is a body control module. Why are you replacing that to fix cooling fans?

[Aaronams25]

I was going to switch it cause the fans only turn on when the car is off and after it had been driven for quite some time. And if I put the key back in the ignition it turns off the fans. Was thinking fan timer control might be the cause.

[F22Chris]

Oooh okay cool. Let us know what happens