Where is the temp sensor for turning on the electric fan? - Third Generation F-Body Message Boards

deesandvees · 05-06-2008, 10:25 PM

I've got this '85 IROC V8 TPI and can't find where the temp sensor is that controls the electric radiator fan. My fan's not turning on (I checked the fan with 12 volts and it does work). I replaced the relay (up by the battery) and followed the green w/ white stripe wire & tan w/ white stripe wire and it looks like they go to the ECM. So where's the temp sensor? I'm guessing the wires from the sensor go to the ECM and tell it what temp the motor's at and then the ECM tells the relay to switch the fan on? Thanks.

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bigj350 · 05-06-2008, 10:36 PM

Passenger side head, in between and just below #6 and #8 cylinder.

86WS6 · 05-07-2008, 02:17 AM

Some of the TPI's have the fan switch located in the front of the intake just above the water pump (California Emissions), however on the majority of cars they are located in the passenger side head.

Kevin91Z · 05-07-2008, 02:29 AM

I've never seen or heard of a factory setup with the fan temp turn-on switch in the front of the intake manifold. I relocated mine there because its easier to get to, and it has a tendancy to crumble and break from the heat in the stock location.

On a single fan setup, the computer does not control the fan. The fan temp turn-on switch in the passenger side head is connected to the fan relay, and when the coolant reaches the switch's tempurature, it grounds the relay which turns on the fan. On a dual fan setup, the driver's side fan is controlled by the computer to turn on at a temp specified in the chip, and the passenger side fan works off the switch in the head like a single fan setup.

86WS6 · 05-07-2008, 05:17 AM

My 86 WS6 is an original low mileage car, with the original fan switch located in the intake manifold. It is a two wire switch, that does not function by grounding the circuit like the models with the switch located in the passenger side head. The port in the head on the passenger side has a factory square headed plug in it. The car is a California Emissions model, and the fan switch is a varible voltage switch that sends it's signal directly to the ECM. Based on the signal from this switch, and from the head pressure switch on the A/C compressor, the ECM controls the fan. There is a another switch mounted directly next the fan switch which is also connected to the ECM, but does not control the fan. In the original Pontiac dealer's service manual, there is a factory addendem that details the wiring diaghram of this model. A couple of years back the switch failed, and we were able to obtain one from the Pontiac dealer. None of the aftermarket vendors listed the switch.

blp226 · 05-07-2008, 09:04 PM

I have a similar question. Please help!!!!! I recently put a new motor in my car andI don't remember which wire/ wires goes to the sensor that tells the fan to come on. My car is a 1984 Z/28 H.O. With the four barrel carb. There are tons of wires and I can't tell what most of them do! Is the sensor in the passenger side head as well, and if so what color/colors are the wires? Thanks a lot guys!

deesandvees · 05-07-2008, 09:44 PM

I replaced the temp sensor today and still no luck, the fan refuses to turn on. The temp sensor on my '85 was on the front of the intake manifold, pretty easy to replace, I just swung the alternator towards the passenger side and removed the bracket to gain access to the temp sensor.

So I've replaced the temp sensor, the fuse, the relay switch (located by the battery) and still nothing. I know the fan works because I've fed it 12 volts and it goes. What else can it be?

Kevin91Z · 05-08-2008, 02:25 AM

Well hey, I learned something. I'm used to the later model TPI's and TBI's and they all have the fan switch in the passenger head, not in the intake manifold. Thanks for the clarification.

bigj350 · 05-08-2008, 06:37 AM

Quote:

Originally Posted by deesandvees

I replaced the temp sensor today and still no luck, the fan refuses to turn on. The temp sensor on my '85 was on the front of the intake manifold, pretty easy to replace, I just swung the alternator towards the passenger side and removed the bracket to gain access to the temp sensor.

So I've replaced the temp sensor, the fuse, the relay switch (located by the battery) and still nothing. I know the fan works because I've fed it 12 volts and it goes. What else can it be?

You probably need a fan switch. For some reason I thought thats what you meant. I would take the Coolant Temp sensor back and see if you can get it exchanged for a fan switch. Thats whats between number 8 and 6 cyliner not the coolant temp sensor like I said in my first reply. There are at least 3 sensors for the cooling system. There is the coolant temperature sensor, fan switch, and a temp. switch.

Fan switch.jpg Fan switch You probably need this one.

Coolant Temperature Sensor.jpg Coolant temperature sensor

Temperature Switch.jpg Temperature switch

deesandvees · 05-08-2008, 02:21 PM

The only other sensor I see is on the drivers side head and one of the wires on it leads to the A/C compressor. That's not the one right?

bigj350 · 05-08-2008, 08:10 PM

You might have to look under the car to see it. Dont mistake for the knock sensor though. That will be coming out of the block. The one your looking for is coming out of the head. It will have a single wire coming out of it. I'll take a picture of mine, just as soon as I figure out how to operate my wifes new camera.

deesandvees · 05-09-2008, 01:54 AM

Turns out my computer is bad. Until I find a replacement I'm going to hook up a switch so I can turn the fan on when needed.

Because of the fan's high amp draw, how do I go about wiring a switch to do this safely? Can I somehow go through the fan relay switch located near the battery?

86WS6 · 05-09-2008, 02:35 AM

The best relay to use is one of the battery switches used for RV's to isolate the batteries. It sort of resembles a Ford starter solenoid except it has a silver finish. The big difference is that it is designed for continuous duty use. It will carry over 100 amps of current, and has three connectors. The small one is the power supply, and the other two are load and supply, which are interchangeable. The switch is made by Tekonsha, and cost about 20 bucks in most RV supply stores. I have one on my T/A and have it carrying both fans. It is switched by an aftermarket fan switch that I located in a thermostate housing with a 1/2 inch pipe thread hole in the top of it. The aftermarket switches can be bought to switch at 180 degrees, or 195 degrees. Use an automatic reset circuit breaker set for 50 amps, and feed the power from a constant hot source. I put mine on the supply wire on the back of the altenator, because it is a number 6 cable, and runs directly to the hot post on the battery. Use a secondary 15 amp relay that allows your fan switch to complete the circuit by grounding the ground side of the small relay, providing 12 volt power to the large relay. Feed the power source to the small relay from the car's ignition, so it will switch off when the key is off.
Its a simple system, that will give you trouble free operation. I have mine connected in conjunction with the existing system, so that if the aftermarket power supply fails, the OEM system will back it up.

Kevin91Z · 05-09-2008, 03:25 AM

Yes yes yes! The correct way is to ground the relay. That way all the current is going thru the relay like its supposed to. If you hook the switch direct to the fan, then all the current is going thru the switch and that will melt the switch!

Check the tech articles or this forum for "total fan control" tech article. The wiring diagrams have been posted.

deesandvees · 05-09-2008, 03:26 AM

Thanks for the detailed info on doing it aftermarket. I will resort to that if I can't get a hold of a computer in a decent amount of time.

Is there a more "MacGyver" way to get this done? I just need to hook something up that works for a week or two (hopefully). Maybe some way to wire a switch that I can put in the car using existing temp sensor and relay?

deesandvees · 05-09-2008, 04:23 PM

Quote:

Originally Posted by Kevin91Z

Yes yes yes! The correct way is to ground the relay. That way all the current is going thru the relay like its supposed to. If you hook the switch direct to the fan, then all the current is going thru the switch and that will melt the switch!

Check the tech articles or this forum for "total fan control" tech article. The wiring diagrams have been posted.

I read through that tech article but how can I simply "ground the relay"? Can I just tap into a wire on the connector that plugs into the relay and go to the negative terminal on the battery or to a ground location on the car? Then I could route it so I have a switch to control that ground? Maybe just have the switch hanging down by the fog lights so it's accessible and I wouldn't have to route a lengthy wire? I don't care if I have to turn it on externally.

86WS6 · 05-09-2008, 09:07 PM

If you want to control the OEM fan relay from a toggle switch, you should be able to power it from an alternative source. You can access power to control the relay from an ignition switched circuit at the fuse block using a tap. Make sure to use a fuse in the circuit, 15 amps will be adaquate. There are plenty of wiring diagrams posted on this site that address how to do it.

oil pan 4 · 05-09-2008, 09:46 PM

I got that "fan switch" for the electric fans I put in my 1984 diesel suburban. It reads OL on my fluke, so it is most likely a switch. I will toss it in a boiling pot of water and see if it closes.
Any one have any idea how hot the switch has to get before it closes?

hotrod85z · 06-15-2008, 06:09 PM

need an 85 ecm with chips? ive got a new 85 870 ecm with both new chips, its for a vette, only diff is a larger injector

nascar2496 · 07-22-2009, 12:45 AM

Ok so i have a question. how is the single fan setup not controlled by the computer when the computer has a wire running to the fan relay. I have a tpi harness from an 86z with a single fan and with the stock 86 chip the fans dont turn on. but with a hypertech chip i have the one fan that i have hooked up to the computer works like it should.

UPDATE: I grounded the pins for the ecm and the fan turns on. and i also read in the book that the coolant needs to be around 234 degrees for the fan to come on. so i let it get hot, and sure enough right as the gauge hit the redline the fan turned on. so its a little warm for my comfort, until i get my chip burned ill just use my manual switch.