Should the main fan kick on first? Or the auxilary? On my stock 1989 L98 she gets to about 215, then the aux. fan comes on. I have never, ever, heard my main fan come on. So, while bored today and reading my manual, it says grounding "b" terminal will kick the main fan on. Sure enough, it works.
But wouldnt the main come on first and be supported by the Aux? Anyone know what the factory settings are to kick the main fan on? Its seems the aux one is set @ 215 as thats when it comes on. Thanks

 

The main fan should come on around 228* (this may vary slightly depending on your readout). The Aux fan (pusher) should come on around 236*. The PO probably put a lower temp. switch/sensor on the aux. fan. to have it come on first. This sensor is between plugs 1 and 3 on the drivers side. Your main fan should come on when the AC is on as well. If not there is a problem.

 

Specs are 226 Main (driven by the ECM) a/c off; 228 Aux through the temp switch in the left head which grounds it's Relay at that number. Aux should rarely if ever come on. Troubleshoot with a scanner and when the Coolant Temp Signal shows 226, the Main should come on. Fan should run for a minimum of 60 seconds and the temperature should drop.

With the a/c, Main Fan is driven by the ECM when the fan switch on the high pressure line opens at around 230 psi. The switch recloses at 190 psi and the fan should cycle off. Use a Manifold Gage Set to check pressure. Disconnecting the switch will simulate the open and the Fan should turn on.

Test the Aux by blocking airflow and with the a/c off, it should come on when the Display indicates 228.

 

That was not the fan on temps on my 1989 when stock. Main fan comes on at 227* by the digital gauge and aux was on 236* by the digital gauge. I changed my aux fan sensor/switch to on at 205*. The car now runs cooler and I still have a 195* stat.

 

Specs are from the Shop Manual and the Digital Gage has nothing to do with the Main Fan - or the Aux for that matter, but you'd expect it to be close since the switch/sending unit are in the Heads. A 5 degree difference between the Coolant Temp Sensor - used for Main Fan Control - and the heads isn't unheard of around here.

As to the Aux Fan, it was a Dealer installed on early C4's in response to overheating complaints from autocrossers and high altitude users and later a factory option. More Vettes left the Factory with a larger (HD) radiator but with only the single fan and plenty of Vettes left the Factory with just a single fan and didn't experience any cooling problems. If it's coming on regularly, something else is probably going on.

 

I should mention, since this has come up, that the manual on 86 from Helm gives multiple fan on temperatures for the same fan (regardless of A/C being on/off).

On my 86 the main fan comes on at 226 and the Aux at 236, if you trust the in-car temp gauge (which you probably shouldnt as old as these cars are, and that its GM electronics).

 

[QUOTE=SunCr;1570850889]Specs are from the Shop Manual and the Digital Gage has nothing to do with the Main Fan - or the Aux for that matter, but you'd expect it to be close since the switch/sending unit are in the Heads. A 5 degree difference between the Coolant Temp Sensor - used for Main Fan Control - and the heads isn't unheard of around here.


Badduck Wrote:
I realize that, I was simply pointing out that there can be a difference because of two different sensors. Maybe your Shop manual says that, but it is NOT gospel. Thinking it through, which GM engineers are not famous for, it is pretty silly to set the on temps. for 2 fans 2 degrees apart. That being said, I have a Z51 car so maybe it was set up differently. Anyway I know where my fans were stock, and bet many more were set up that way.

 

Thanks guys. I guess my next move is to disable the aux fan and see if the main kicks on. AC is so worthless I never use it.

 

The Gospel according to GM is wrong? I'm on my well worn 2nd - same as the first except the schematics are now Black/White instead of Color. Errors were corrected with Service Bulletins (and there are several, but none for the fans). Scanning is the diagnostic method outlined in the Trouble Tree. And, starting with the engine cold and comparing it to ambient will give you some idea as to how accurate that signal is. Until you see the CTS signal, you can't diagnose anything, so that makes sense doesn't it? Show us your scan numbers and we can provide input if it needs to be fixed, but if the ECM isn't driving the fan when it hit's the spec, the solution is pretty simple (assuming the Relay and wiring are good). Your suggestion that we accept your Dash Readout as to what it should be is a bit much, but you continue to hold out that it is everytime this comes up. Get a clue - or at least get your own Manual and a Scanner.

There are no differences for any of the options including those that only came with a single Fan. These specs were used through '91 or the last L98 even after the switch to dual suckers (which was made in anticipation of the additional cooling needed for R134). Those Years and most cars only need a single fan to control coolant temps with the compressor off. Other than that, if a running fan doesn't drop Coolant Temp, something isn't the way it's suppose to be.

[QUOTE=BADDUCK;1570852022]

 

For those who have faith no proof is necessary, for those who don't no proof is possible.

 

Ok, so after your help and a little detective work, the aux fan, which runs off the sensor between plugs 1&3 kicks on at 215*. Upon disconnecting it, the main fan does come on at 227* so it is working. It just appears, as someone said earlier,a prev. owner must have installed a lower temp sensor for the pusher. Since Im not overheating, I really dont see any reason not to leave it, do you? Thanks everyone...

 

That was my guess as I said in my first post. I wouldn't change anything, it's a good setup. I put in a 205* sensor in mine, but 215* is good with a 195* stat.