SOLVED: replaced fan thermo switch on stat housing. Required a 24 mil wrench (15/16). Rad fan now turns on 95 - 98C according to ECT sensor. Dash temp gauge is now stable around halfway point.

First time posting

The temp gauge on my EM1 will spike after a hard drive with the heat off. By spike I mean hit 3/4 of the way up until the fan kicks on. I've had 2 EG hatches with D15s in the past and the stock temp gauge never moved as far as I can remember regardless of the heat being on or off.

To get to the point, is this normal?

According to my OBD reader I can see that the coolant is a stable 84 to 86 Celsius after a hard drive with the heat on, but when I turn off the heat it will steadily climb up to 110°C. The stock dash gauge won't move until the temperature passes 96 and it'll peak at just shy of 3/4 to the top when the coolant hits 110 and then the rad fan will kick on and bring it down. Is this normal?

The techs at Honda verified my fan, fan relay and ECT sensor all work and noted that the fan would turn on for them at around 104 which is apparently normal. They said they weren't sure about the gauge moving though. I've just never seen a stock temp gauge move so much so I'm sceptical.

My car is bone stock and has had a new ECT sensor put in and a new tstat, and yes the cooling system was bled after.

Any input is very appreciated

 

Did you use GENUINE Honda parts for the thermostat and engine coolant temp sensor ?

 

Yes all parts are OEM. I find it bizarre that the dealership would call the temp gauge bouncing around "normal".

 

I think you might have to go to a different dealership for the diagnosis.
Your fan is definitely not turning on at the right temperature.
According to the Honda specification, both Civic/Integra fan should turn on at 91-95C (196-203F).

Your fan switch is definitely not working as normal if the fans come on at 104C.
After you get that switch replaced again, I would also re-burp the system and check radiator cap as well.
Good Luck

 

By the way, these older Civic/Intergra have 3 Cooling sensors.
There are
1. ECT Sensor for the ECU (2 pin at the head) -purpose is to provide temperature data to the ECU
2. ECT Sender for the gauges (small single wire at the head) - purpose is to provide temperature data to the gauge.if you have gauge issue, this might be the cause too.
3. Thermo/ECT Switch for the fans (2 pin located at the thermostat housing) - purpose is to turn the radiator fan on and off. it's a very simple binary switch that turns the fan on/off

If the fan turns on at 104, your thermo/ECT Switch needs to be replaced.

 

Thanks Kmvguy83 for the info. I used an IR thermometer on the fan switch and ECT sensor and the thermometer matches my OBD data pretty exactly. Not sure what the dealership was on when they diagnosed my B16. The engine hit 98C and the fan still didn't kick on.

I'll be installing a new fan switch tomorrow and see what happens.

 

Besides the thermo switch, the ECU should be able to activate the fan too. If either the thermo switch or the ecu takes the fan relay circuit to ground, the fan should turn on.

Do you have a cooling system pressure tester? I got one the other day, figured out my auto civic doesn't have bad headgasket, it was a leaking hose clamp that would slowly introduce air into the system, then cause it to overheat to 3/4, and push coolant at times too (over expansion).

 

Is this also true for the stock ECUs?
Seems like Hondata/HTS can override the thermo switch but I'm not sure about stock ECUs.

 

Thanks for the advice, I'll see if I can borrow one from a friend. New fan switch installed tonight. Will go for a drive and see if there's any improvement.