Ok, I recently got me a 87 Formula, 5.0 TPI (59,xx miles!!!...but the odometer died shortly after I got it...grr...) Anyway, one problem I'm having is that the cooling fan is always running when the motor is running. Unless someone messed with the wiring, my guesses are the sensor for the a/c (same prob with my V-6), or cts (any other suggestions?). Problem is, I dont know where the cts sensor is on this motor. I searched and people say the one in the intake manifold controls the fan, but others say the one on the passenger side controls the fan (single fan btw). Anyway, can you guys tell me what the sensor in the manifold and the one on the passenger side are for and whioch controls the fan / tells the ecm to turn on the fan? Thanks!

The fan is controlled by the computer from temp readings it sees from the CTS; not directly from the CTS
Pass side should be temp gauge sender

Sounds like someone grounded them out to keep them on

why would you want to turn them off
install a rocker switch inside for one fan to turn it on when you need it
the factory settings will not turn the fan on till 210* a lil to hot for me

Either one could be the problem, one on head turns fan on at a set temp, one on manifold tells ecm the the temp for various thing and fan control, thre are two on manifold one has a square plug that is for cold start injector, oval shaped is for temp to ecm. If there is one on drivers side also it should be for your temp gauge. unplug the one on the head see if the fan shuts off.

Next to the batery mounted on th side theirs is a small black box tahat is for the fan i messed with my wires and mine was fine

Thanks for the advice guys, I disconnected the one in the picture above on the intake, and the fan still runs. Where is the sensor on the passenger head? Also, where is that box by the battery? I cant seem to find either.

look between rear two exhaust ports on passenger side. on drivers side between front two. also check the relay, could be stuck on, I think thats the black box he is talking about.

Hello 1989karr!!

The fan relay should be your culprit!! The sensor in the passenger side head on a 305 TPI single fan is basically a redundant sensor, in otherwords, it doesn't do anything!! The fan turn on temp is controlled by the CTS in the front of the manifold, it feeds the temp to the ECM's PROM chip, which is hard coded to turn on the fan at 235 degrees F. If you had A/C with the dual fan set up, this sensor would control the second fan turn on temp!!



If your fan relay checks out, it's possible that someone wired the fan to be on all the time, check for strange wiring!!

hrrmm...ok, i checked everything, but it seems taht the fan STILL remains on!

Is the fan relay on the driver side by the firewall? I disconnected all of them, one at a time, and the car runs....and it runs fine!!!...I imagine that disconnnecting one would do something right??

Also, I found ONE ground wire that looks a little out of place, but it seems to have a factory crimp on it, disconnected it and nothing changed.

I gave this car a better look, and seems they have a bunch of performance parts on it. Is it possible that they changed the PROM which has a program to keep the fan on all the time??? I have driven this car around the island....and it seems to perform flawlessly, but id prefer to have the fan come on when its supposed to.

Thanks guys!

The fan relay should be on the passenger side radiator support near the air filter can, you may need to remove the air duct to find it.

YES!! the eprom could have been flashed.. and a custom temp setting in place of the factory.. take a look @ your ECU under the passenger side dash
look a eeprom replacement or a after market vendor

trace your fan wires & relays next to the passenger side headlight look for a spliced line near the relay that may have been grounded out to the body ground


it's to your engines benefit to keep your coolant temp lower then 200*

ok i found the relay!

i disconnected it and the fan stops. reconmnected it and the fan runs. i got a replacement on the way...im hoping this is the problem....the relay rattles when i shake it....also, it looks like its been resealed with some kind of glue???

well, if its not the relay i have no idea what it could be except for the prom. but like you guys said, maybe its better to have it running all the time eh?

another thought - if the car has AC - on the pass side is a pressure switch in the AC line which also controls the fan (to turn it on when the AC is on and the compressor is running) if it's jumpered that would cause the fan to run all the time by energizing the relay. Never know what people do some times.

totally true...... i plan to post about my s-10 and "larry's awesomeness" in the most ghetto thing you found thread lol

I checked that switch but it seems ok. when the new relay comes i'll let you guys know what happens

Switch is not connected to fan relay.Only factory input to relay is from the ECM. Pressure switch is a signal wire to the ECM which goes open circuit when the A/c is on.
You have to jumper the switch when you do the A/c delete otherwise fan will run all the time.

Could still be faulty switch , pull the connector and jumper the two pins to see if fan stops

good catch - mine is not that way but I have the duel fans not a single. mine grounds when closed (AC on) and turns on the second fan.

...ookkkaaayyyy new relay is in!....and the fan still comes on!

Well, the old relay looked nasty anyway and rattled....

Ok, I ASSUME the PROM has been changed....but is there anyway to verify / check this? Also the plastic connector for the fan relay kinda stumps me..let me explain as best as I can.

The plastic connector that goes into the relay, on the bottom has I believe, four sections for the wires...like this ----> [][][][]

Basically one block per wire. So there should be 4 wires.

One of them has an extra wire going into it. So that makes a total of 5 wires going into that plasctic connector. HOWEVER, it looks like it was stock, and it goes INTO the plastic connector, not spliced. Is this supposed to be like this? It looks like its from 1987, and it even looks like it was done at the factory, so Im a tad confused here....lol

I've got the shop manual for this car - let me see if I can scan the page tomorrow showing the circuit. 3.4 '89 right? single cooling fan? there are several configs for this so I want to be sure I get the right one.

thank you knight 123, actually, its almost identical to what you have, but its a 1987 5.0 TPI Formula i recently picked up. Anything and everything is much appreciated though! Perhps the wiring is similar?

sorry I was not able to get it done today - crappy day at work. I will try and do tomorrow for you.

You can go to autozone.com and view and print the wiring diagram from a chiltons manual.

Ok so here is the pic - not very clear though. looking at this the ECM closes it's relay when the temp is right - then assuming - it also shows a second switch outside of the ECM that will ground when the temp reaches a little higher limit. Since the relay needs a ground to engage - removing the relay should turn off the fan - if it does not then you will need to trace the wires since it may not be the fan relay you disconnected. This second temp switch that grounds the relay is located in the pass side of the engine - UNDER the manifold YUCK! Hope this helps some.

here is another view of the left side of the page showing the econd cooling switch...

thanks very much knight 123!

mmmmm ok, I looked at the diagram, and looked at my car, and everything seems to be fine! (I'll probably take it to my mechanic to look at....dont worry, I trust him to do all the things I cant do or figure out)

Its just that the fan comes on constantly!

I think at this point, looking at all the cars "accessories" like the exhaust, performance rad, intake, wires etc...I wil lassume that they reprogramed the PROM or something. Would you guys recommend that I leave it like this? I knwo I'll go through a lot more fan motors, but then again this car probably wont see to much driving time

NP! If they did reprogram the chip I would let it run if it does not bother you. Heat can create all kinds of issues so moving some air at the lower speeds won't hurt I'm thinking. Also be good to figure out what else was done just so you know in the future. Good Luck!