Back to L98GTA home

Sep 09, 2023

Please be patient while I get some updates to make the current info much more clear...

Given the completely closed front bumper cover on these cars, air flow across the radiator is so low... little wonder these cars have a history of running hot.

The entire cooling system has to be at its peak or in 95 F degree heat you will likely see coolant temps up in the 220-225 range or higher!   This is too high for me personally

In my quest for more knowledge about controlling the MAIN and AUXILIARY fans on my 89 GTA, I used the GM service manual and these drawings.

1989 Factory Manual Coolant Fan wiring TPI V8s  5.7 and 5.0

The above diagram is for 1989 cars with the L98 or 305 V8 Tuned Port Injection TPI.   The TBI L03 is slightly different

I suspect this setup may be applicable to 90-92 3rd Gens but do not have the wiring diagrams to prove that.

This assumes a VIN8 (L98) 1989 GTA )  What I have found is the AUX fan (passenger side) is controlled by a 238 degrees F thermal switch on the right side of the engine above the starter motor AND ALSO by a pressure sensor/switch on the passenger side coming from the AC high pressure line (at 233 psi).  So the AUX fan will come on under either (or both) of two conditions.  Engine temp above 238 or AC compressor pressure being higher than 233 psi would kick in the Aux fan.    238F is REALLY way too high!!

The MAIN fan (driver's side) senses engine temp, and GM decided to set this one WAY up there too, like 230 or so, and it is controlled by the ECM.  Temperature here is sensed via the sender on the drivers side of the engine.  This sender feeds engine coolant temp (ECT) to the ECM as well as the temp gauge on the instrument cluster. 

Each fan system has separate relays, and on VIN 8's (L98's) the one on the passenger side fender well is the AUX relay, the one real close to it and on the radiator core support is the MAIN fan relay. On VIN E's ( 305's ) I believe the MAIN fan relay is on the firewall next to the fuel pump relay.

 I had trouble with my MAIN fan not coming on till the car was already overheating, same with the AUX.   Determined to fix it I purchased an adapter for EEPROM to Flashable chip, and a burner called Flash and Burn.  Both were purchased from Craig Moates. 

I then used TunerCat to set the MAIN fan value to 185 on and 176 off and then changed the Aux fan sensor to a 195.    Car never overheats now. 

TC's product is just the best there is, period.  Craigs chip burner talks directly to TunerCat.  Very sweet.

Craig is no longer in business, I am not sure who might sell his chip adapter or burner at this point.

Gerry-

gem 09/09/2023 11:06 AM