2007430

97 Civic LX

Cars been running hot and I noticed the radiator fan is not kicking on. I turn on the heat to cool down the engine and the weird thing I noticed is when I turn on the heater the radiator fan comes on immediately. What I don't understand is why does the radiator fan come on when I turn on the heater, I can imagine it would be normal for the condensor fan to come on but that does not come on. I'm wondering if that is normal operation?

As always thanks in advance for any replies, and I will be out in the morning with my voltmeter taking some measurements across the sensors, if anyone has anything particular they think I should look at please let me know.

beecee18

Thermostadt pronto

Condensor fan will only activate upon the air conditioning being toggled on.
If you are going to check sensors I would be checking the fan switch which is located on the thermostadt housing right there while your replacing your thermostadt.

I like how your screename is just a #
just a slave of the system huh!

RussLaviolette

iTrader: (2)

I would take a look at the fan switch, located near the thermostat. It could be that it's not signalling to initiate the fan, but activates it when the heat is turned on.

beecee18

Coolant temp switch can be found on the side of the cylinder head,
the fan switch is located on the thermo housing.

RussLaviolette

iTrader: (2)

Your correct. I was referring to the fan switch.

2007430

Fan switch is what I was leaning towards as well. Now I have to ask what makes you say the t-stat could be causing this? I was not really considering the t-stat simply because I was thinking its an electrical issue if the fan is not running but when I'm looking at the car I will check if the hose coming out of the tstat is getting hot.

My screen name comes from me pressing random numbers when it was time to make a name, it keeps me anonymous from the system.

Now I'm wondering, why will the fan switch signal the fan to come on when I turn on the heat? That does not make sense to me, is that normal operation?


Looking at this diagram (which I found with a random google search and am hoping its correct) it does not appear the heater should signal the fan on.

RussLaviolette

iTrader: (2)

I'm not fantastic at reading wiring diagrams, but it appears that the "HTR, A/C RLY" is connected to the "RADIATOR FAN RELAY." You can possibly test the fan switch by jumping the plug that connects to the switch.

2007430

Hi, actually that is a fuse that acts as a common power supply to the radiator relay and the condenser relay. I will definitely try jumping the connector.

While we're on topic about the diagram I was wondering, on the ground side of the fan switch was is that icon in the box with the arrow? I'm thinking its a thermistor? Is that the actual temperature sensor?

Thanks allot guys

hondaguy777

It's prob a dumb question, but imma ask neway lol. Is ur a/c button pushed in? Even if you have the heater going, the condenser fan will still kick on if the a/c is activated. I'm just going off of memory though haha.

hondaguy777

Lol, nm... I feel dumb now. I just read that you were talking about the rad. fan haha. Muh bad

beecee18

Well if the thermostadt is stuck shut, the coolant would never pass by the fan switch for it to activate the fan,
You need to find the flow chart found in the service manual that give you the proper way of testing the switch.
Testing the thermostadt is a nobrainer and requires a pot of water and a stove.

2007430

A smart man once told me he learned everything he knows by being 'the village idiot' no matter how dumb a question he would ask it.

That makes sense about the coolant not getting to the switch if its stuck closed, I will look into that. On these cars the tstat is so cheap and so easy to change that I figure if I'm removing it to test it in boiling water I will replace it while its out.

I will post up my results with everything, thanks guys.

barcode31

I'm havin similar probs outta my d15. My fan never comes on but the car never runs hot according to the temp gauge on the dash but the car starts idling erratically after about five mins when it seems the fan should kick on. Just found this two days ago and haven't had the time to test anything yet.

2007430

Gents, and ladies? I have two updates for you, both of which make me feel stupid but I will take these as a learning experience and will share.

First off, I was looking at the wrong fan I was assuming the one in front of the engine was to cool the engine, then I looked again and thought wait a minute, the condensor is behind this fan therefor that fan is cooling the condensor and the radiator is on the passenger side so this other fan must be the radiator fan, doh.

My next stupid. About a month or two ago I replaced the t-belt/water pump and I did a quick coolant bleed. Since then I haven't drove the car much (I have another car too) also we haven't had any real hot days until now. So last night I was thinking maybe their is a chance I have air trapped in the system still, I bled the system again last night and did it very thoroughly, this morning I came to the car and found the level dropped, I topped it off and drive about 4 miles in 80+ degree heat and found the gauge stayed centered and at stops the fan does now kick on! I will consider this to be fixed. My suspicion is their was a large air bubble trapped right at the sensor.


Now, lets see if we can fix Barcode31's problem.