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.

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

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.

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.

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.

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!

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?

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.

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

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?

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.

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?

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.

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.

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?

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.

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.

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?

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

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.

What in the hell is all of this talk about a fan switch on the passenger side head? That is for the secondary fan!!! That doesn't do ****! The main fan (driver's side is controlled by the ecm through the coolant temp sensor on the front of the engine above the water pump. The ecm turn the fan on at around 200 + degrees. Too hot IMO. Secondary fan (passenger side fan) doesn't turn on until around 230 degrees. This fan usually comes on only under extreme conditions or when running the ac. You can, however just cut the wire going to the fan switch which is located between no. 6 and 8 cylinders. The wire going to can be grounded to the body of the car (for full time operation) or ran to an on/off switch so it can be used at will. LOL

Hi, Go here and scroll down to NINA's post. There are clear and easy to follow diagrams for a manual switch if you have the single fan system http://www.thirdgen.org/techboard/co...wont-turn.html (Cooling Fan Won't Turn On...) Happy cooling!

Wow good job, really detailed Mahalo for the help.

ok WTF, there are about 30 contradicting statements in this post.. i am currently dealing with this situation as well.. SINGLE FAN TPI coolant temp sensor in the passenger side head controls the fan, green / white wire from fan relay goes to ecm then back to coolant temp sensor. replace sensor and check wires if relay and fan motor have already been checked.. as a temporary work around ground the green/white at the fan relay to the negative batt terminal with alligator clamp wire and when car is turned on the fan will always run

Some were contradicting because the OP has an '85 like me, They don't have a passenger side temp sensor, just a block off plate.

Your 87 should be fine replacing the one between 6 and 8 on the passenger side, might wanna wait for more answers though because i'm not sure why else it wouldn't be cutting on.

If I am correct. All you need to do is ground that wire to the body of the car. That will complete the circuit.

Yeah, If you ground that green and white wire that goes from the fan switch to the relay with the key on and your fan relay and fan work the fan will run. Any old body ground should be fine. Putting a switch between ground and the wire would give you more control if you want it. That's all the fan switch does- ground the wire

Try grounding that wire like I told you and see if your fan comes on. I am used to the TPI set up with dual fans. There is a fan switch between 6 and 8 cylinders. I , first cut that wire and then grounded it to the body and the fan came on. So, next i just used my foglamps switch for a switch.LOL Basically it should be like this: You should have a coolant temp sensor somewhere on your motor. Ok, that tells the ECM your temp.Next, your ECM turns on your fan. It is that simple. If you want the fan to turn on all the time, then just ground that wire to the body of the car and it should come on all the time. I don't recommend it though. Your fan could wear out quicker. You should actually look into buying a fan controller and get a lower temp thermostat.

200 degrees is way too hot to run your engine IMO. Especially in the summer. Your car will have MORE power running at 180 or even 160 degrees.

Very nice dude, it all makes sense now. So the fan switch in the head operates at a certain temp, thus flexing a lever inside to ground the circut out thru the threads on the unit into the motor.

I've been reading for hours and have this huge headache just trying to ground a fan relay. Willie talked alot about kits and different fan temps but nothing about how to simply ground a relay in his article. My water temp sending unit is what appeared to be broken since the stock gauge doesnt read anything but in fact it was the secondary fan switch. So, I'll just use that end and route a manual switch and be done. Just rebuilt the motor and have been in a tussle with the damned factory cooling system running at 230-240 in traffic, was pissed! Can't believe GM would run motors without a fan till 220... What a nightmare finaly at debts end.

I am posting not only because it feels good to finaly fiqure it out but also so theres one more post that someone might find in a random search like I did.

Thanks to all.

Just remember , in order to turn on fans earlier. You will need the programming in the ecm done too. I believe factory programming doesn't turn on your fan until about 210-215 degrees. Then, the secondary fan comes on at about 230-240 degrees. Not sure of the exact number. I use a hypertech thermomaster chip. Fan comes on at 176 , i believe and i am also using a 160 degree thermostat. Does give the car more power.

Also, remember not to run your secondary fan too much. You don't want to shorten it's life. It is good insurance though.LOL. I think your best bet really would be the Ford Taurus fan and an aftermarket fan/voltage controller. Flows 4500 cfm or more!

Even though you're replying to an ancient post... that applies to dual fans. TBI and the LG4(w/elec fan) used the fan switch only.

ECM controlled fan turn on is 220°F. The fan switch, afaik for all years, had a turn on temperature of 238°F

It's the exact same fan as the primary, what does it matter if it runs just as much ? It's harder on your alternator than it is the fan.

In '88-89+, the dual fan wiring was changed anyways to call both fans when the A/C was turned on.

'87 was primary fan ran for everything. The secondary was just, kind of there. I think 85 and 86 TPI had single fans (86 may have had dual available), I don't recall exactly.

Single fan control varied by year/engine.



Changing turn on temperature is as simple as changing or adding a new fan switch. Granted, in the case of TPI dual fans, the secondary would simply become the primary if the turn on is lower than 220°.

Cause that secondary fan is your back up fan really. Oh well, fan motors are only $45 anyway. LOL 220 degrees is way too hot IMO.

That makes it a primary fan with the A/C on. Secondary only in relation to cooling.


220° is also plenty fine for a stock car needing to meet emission regulations (during it's production years). It's yet to cause my '91 @ 214,x miles. Unless that is considered low mileage. My '84 (literally) fell apart at 280,x mi. but, the motor still ran fine. My 'bird made it to 139,k before I just started tearing it down. So if you are to say it (temperature) affects longevity, isn't a 100% true statement.

There is also no sense in running the engine any cooler as a nearly stock motor won't gain 20+hp from running 160° or, 180°. At best, it will use slightly more gas and have slightly better throttle response.

I'm not saying it's bad to do but, people act like a stock pos motor is going to magically run like like a top fuel engine just over running it a few degrees cooler.

A lower thermostat also does not cure overheating. If a car is running to 240° and not cooling off with a fan, a low t-stat is not the issue (unless the current one has failed).

JMO as well.

[quote=deadbird;4664972]That makes it a primary fan with the A/C on. Secondary only in relation to cooling.


220° is also plenty fine for a stock car needing to meet emission regulations (during it's production years). It's yet to cause my '91 @ 214,x miles. Unless that is considered low mileage. My '84 (literally) fell apart at 280,x mi. but, the motor still ran fine. My 'bird made it to 139,k before I just started tearing it down. So if you are to say it (temperature) affects longevity, isn't a 100% true statement.

There is also no sense in running the engine any cooler as a nearly stock motor won't gain 20+hp from running 160° or, 180°. At best, it will use slightly more gas and have slightly better throttle response.

I'm not saying it's bad to do but, people act like a stock pos motor is going to magically run like like a top fuel engine just over running it a few degrees cooler.

A lower thermostat also does not cure overheating. If a car is running to 240° and not cooling off with a fan, a low t-stat is not the issue (unless the current one has failed).

JMO as well.[/q

But running an engine cooler can be a simple fix which creates so many positive side effects in which case everyone should fix if emissions is out of question.
If you think 220 is ok then thats you specialy for an older motor. whatevs, no big deal.
For sure though, lower temps create much better fuel/air mixture and less damage to rod bearings and piston rings which are important if you want your motor to keep good clearances for example, longevity of descent compression and less blowby. With our race motor, if it gets up to 240 then I pull it off the track and spray the radiator down with water no if ands or buts. Of course there we deal with high compression over 350psi and also alumninum heads, in any case it doesnt matter, theres no reason to try argueing that running a motor cooler doesnt really matter, no matter how old it is.
It is easy to get carried away with small enhancments but hell, my best friend just spent 1200 on new exhaust for his 4th gen. Sometimes people love every bit they can get

I added a toggle switch (inside the car) to ground that temp switch wire (between cylinders 6 & 8) ... Now I can turn that on anytime I want, and it still operates factory style if I don't. I like cooler more than hotter, so keeping mine in the 190 range is preferred. The driver side comes at 220 (ECM), or when the A/C is turned on. The passenger side comes on at 238, although it's never gotten hot enough to. Alternatively, I can flip that switch inside the car and turn the passenger one on (by completing the path to ground). When I do that about 190, it never gets to the point where the ECM would be kicking on a fan. Works for me!

Mike

Hells yea. My secondary fan switch turns on both fans. Something ain't right but it sure works for me.

Wrong, wrong, wrong! There are 2 pieces that look the same. The one on the intake manifold base is the coolant temperature sensor. It tells the ECM how hot the coolant is which then the turns on the main fan. The other is called the Temperature fan switch which turns on the auxillary (second fan) when the coolent reaches a certain temp. Good info should always be excercised with correct info.

[quote=DuBree 87;4668362]Wow, that's almost Lingenfelter advice there with those wise words. Thanks, I've changed my way of thinking due to your eloquent words of wisdom.

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