I have a 1987 IROC 5.7 with dual fans. My primary fan motor gave out three days ago. I replaced the fan motor and while testing it, with the car running and in park on a hot day, I noticed that the primary (drivers side) fan doesn’t come on until my dash temperature gauge is almost in the red. Once it comes on it will cool the engine to around 220 and then turn off. My secondary fan never turns on.
By doing some research I’ve found that in 1987 the primary fan is turned on by the ECM and the temperature at which it is turned on differs. The secondary fan is activated by a temperature switch in the passenger side of the engine block or when the AC is turned on. The AC has been removed so I can’t test if the second fan is working.
Am I right in assuming that if I replace this temperature switch with a lower temperature one SW505 (213 degrees) or the SW555 (204 degrees) that my secondary fan will turn on first and cool the engine without the engine getting too hot. Then the primary would be a fail safe and turn on normally at the higher temperature if something happened to the secondary. Thanks for your help.

 

That is correct

 

On an '87. the secondary fan gave no s--ts about the a/c. The secondary fay was a tacked on solo cooling fan. As scooter simply says though, lower fan switch (temp from ecm) temp will make it primary over the ecm switched fan.

 

Hello, I would like to get the same thing, I haven't no A/C and if I can active the second fan, for get less heat

but where is this switch ? (sorry I am french and it is my american car .... GTA 87) ? and where I can find this SW555, for buy it ?

Thanks for your feedback

 

That's how I have my 89 setup.

 

https://www.rockauto.com/en/catalog/...an+switch,4312

 

I have an 87 GTA 5.7L as well. Dual fans. Neither will come on no matter what. I tested the fans with the paperclip in the OBD, and both work fine. My first thought was to replace the CTS and both relays. The CTS and relays are OEM, but now I am reading relays seldom fail. Any suggestion on what I should do next? Car is low mileage, no cabling issues, radiator recently flushed, pristine condition.

 

You can assume GROUND and POWER wires are OK because the fans did work when the ALDL was used.

"Jump" the GREEN / WHITE stripe wires @ each of the relays with a negative wire and see if the fans work........ If they work OK then the problem is possibly the ECM & or ECM temp switch, or the Temp Switch in the pass side head. If they do NOT work the problem would have to be the relays, or the FAN fuse, or the Fusible link. This is from the 87 Shop Manual.

 

just listening.

 

INFO valid for TPI
>> Primary Fan in controlled by the ECM. It reads temperature using the Coolant Temperature sensor beneath the thermostat housing and activates the Primary FAN (Drivers side) based on the set temperature in the PROM. Mine was set to ON at 220F and off at 195F. I changed that to 200ON / 190OFF. The relay for this FAN is on the side of the radiator support (Passenger side) and you can see if it is working by grounding the thin Green / White wire on the relay.

>> Secondary Fan is controlled by the passenger side head fixed temperature switch (stock 238F) or the AC pressure switch. You can test by grounding the wires on the passenger side head switch or shorting the round AC pressure switch. I changed mine to 220F to be used in case of primary fan failure. Relay for the secondary FAN is on the passenger side near the coolant tank. When the secondary FAN is ON, the ECM gets feedback and ensures that the Primary FAN is also kept on while the Secondary FAN is running even if the temperature falls below the set OFF temperature in the ECM.

As a third option to use the Secondary FAN better, I also wired a timer module triggered by the primary fan signal which starts counting down to 4 minutes after which it will also power on the Secondary FAN. This will be when you are idle in the traffic and the primary fan takes more than 4 minutes to cool down to the OFF PROM temperature. I simply wanted to share the load across two fans and be able to bring the temperature down quicker without putting a lower fixed temp switch on the pass side head. I don't like the option of lowering the fixed switch as it is not controlled by the ECM and if the engine temp is higher than the set temperature of the switch, the secondary fan will kick in before you start the car and I hate that.

NOTE. Whoever is interested in putting a timer to activate the secondary fan relay, you need to put a diode going towards the ECM to block the feedback signal from the timer output or else the ECM will think that the secondary FAN is on due to high temperature or AC ON and will also keep the Primary FAN ON indefinitely.

 

">> Secondary Fan is controlled by the passenger side head fixed temperature switch (stock 238F) or the AC pressure switch. You can test by grounding the wires on the passenger side head switch or shorting the round AC pressure switch. I changed mine to 220F to be used in case of primary fan failure. Relay for the secondary FAN is on the passenger side near the coolant tank. When the secondary FAN is ON, the ECM gets feedback and ensures that the Primary FAN is also kept on while the Secondary FAN is running even if the temperature falls below the set OFF temperature in the ECM."

on a TRANS AM 1987 GTA, the secondary fan run only with the switch temp near of the knock sensor ? (and without A/C who works ?)

 

87 GTA is the same as I described. Secondary fan is triggers by the passenger side switch IN THE CYLINDER HEAD. The knock sensor is on the same side but it is further low in the engine block. The temperature switch is vertically above the knock sensor but in the cylinder head. It has the same type of plug as the knock sensor.

With or without AC doesn't matter. If you don't have AC then it will be controlled ONLY by the cylinder head temperature switch.

 

ok then, I buy a new temperature switch with a lower temperature one SW505 (213 degrees) and my secondary fan will work (just become the first fan to run, before the primary)? and with or without A/C working

 

Yes that will work but if you cannot program the ECM for lower temperature activation i would get a 204 degree switch at least as 213 is already high in my opinion.

TS85 @ 211F
TS136 @ 204F

You should also check your stat rating.

 

Hey guys, original poster here. So I replaced the fan temp switch on the pass side of the block with SW555 and after buttoning everything up and turning on the car now the primary fan is constantly on from start up. Previously my primary fan would only turn on when the temp gauge was in the red and my secondary fan would never turn on which is why I replaced the temp switch with a lower one but now the primary runs as soon as the engine is started. Any ideas?

 

Bad fan switch

 

Bad fan switch? I was under the impression that the fan switch controls the secondary fan and the ECM controls the primary.

 

Try unplugging the fan switch. Like scooter mentioned it could be shorted out.
if the secondary fan stops when disconnected.
is the ac turned on ?
have you checked the green/white wire to the primary fan to see if the ecm is controlling it causing it to be on.

 

The secondary fan is not turning in at all cuz the temp will never reach the turn on temp of 205 if the primary fan is constantly running.

Before I changed the fan switch the primary fan wouldn’t turn on until my temp gauge was in the red. My secondary fan wouldn’t turn on at all. I installed the lower fan switch with the idea that the secondary fan would turn on first (at 205 degrees with switch SW555) and the primary would be a fail safe if temps reached that high.

But now after installation my primary fan is constantly on when the engine is running.

I will unplug the fan switch and see if that makes a difference.

 

We are all assuming that no one messed with the wiring. Are you sure the primary fan is still wired stock? Did you try shorting the wire on the pass side head to ground and confirm which fan switches on?

 

me who wanted to do the same setup on my trans am GTA ? same idea with a temp switch T85 (212F) and I want to run the second fan before the primary fan who run too late .....

I hope you find the solution...

 

Part # TS85 Fixed it for you. Standard Motor Products (SMP) website call it temp switch with light It does not state a turn on temp!

 

That's my Guess,.... AC is probably ON.

+1.


The fan switch in the head is in no way related to the primary fan. Changing that switch in the head should not have done anything to the primary fan operation.

** Apply ground to the secondary fan switch wire,... the secondary fan should operate.
** Check to see if the AC is turned to any setting other than OFF.

 

My AC has been deleted. No ac radiator, compressor, condenser. Currently my stock blower box is out of the car while I paint my ac delete blower box and get it ready for install. Is there a wire that was cut that may be causing the primary fan to run constantly? I will take a look tomorrow. Thanks guys.

 

The blue wire from the ECM to the no longer present fan pressure switch needs to be grounded to prevent the primary fan from running at all times ( '85-87 TPI ).

 

Thank you deadbird and the rest of you guys for the help. That’s exactly what it was. I plugged the old connector into the wire and that did it. Now I have to find out why my secondary fan isn’t coming on at 205 degrees with the new switch. I think the fan motor might be shot. Thanks again guys. TGO is a great resource.

 

Is that the AC switch in the line down low, or the one on the condensor?? Both my fans run all the time when the motor is running. Thanks

 

Pictured above is the switch that screws into the condenser.

 

Thanks for the info.
I have a 180F thermostat in my car, so I ordered a TS136 switch at Rockauto.

 

So today I took the original GM switch out easy ( although almost all the coolant came out as well...)
Anyway, the new Standard TS136 went in easy as well, but it's not flush with the head, like the original switch...
I'm sure it's not cross threaded or something, but It's not going in all the way, is this normal?
I still see some threads and white tread sealant...

 

No it doesnt need to go all in and its normal you still see some thread. As long as no water leaks its fine. Dont force it too much or you could crack the block!! Probably the stock one managed to go all in due to thinner thread sealant.

 

Thanks, that were my thoughts as well, but still asking for piece of mind.
Going to fill the coolant later today, hope it's not leaking.
As I'm working under the car right now, I'm going to adjust the hand brake....pita job, no space to work with spanners...
How are things at Malta?
Been there many years ago, planning to go there once more when Covid is gone..!!

 

Putting COVID aside, things are pretty fine. But as I said, putting COVID aside is a big thing to assume.....

 

No leaking, day well spend so it seems.