Hi everyone, I tried doing a search and seems like all the problems that I could find are opposite of what mine is. My 86 has 2 fans. The electric fan comes on at 180deg. Stock is supposed to be 2xxdeg. The only thing i've done do the car was replace the radiator cap, tstat (180deg) and hose. Could there be a lower temp fan controller installed? I don't think it needs to come on that low. Im rarely in stop and go traffic during high heat situations, when I have been it hasn't overheated. So is this simply a lower temp controller or something else?

Thanks!

Scott

 

Is your temp gauge reading correctly?
Need to check your wring to see if a PO has bypassed the computer control of the fan by wiring to a lower temp switch in the head
Or check the memcal ( chip ) in the computer to see if a non stock one
(with different fan temp ) has been fitted

 

Just to clarify, is it the main fan in front of motor, fan in front of rad or both ?

 

Try to learn the basic design of the system to fully understand whats going on now and see whats actually changed...

Fans on at 180...probably too low for that car. Stock or semi-stock needs to run a bit warmer. A range of 185 to 210 is what most people like...or feel comfortable with. Its really more about what the ECM "tune" wants. Whatever the program ask for is what the fans and accessories need to deliver.

Main fan (sucker/engine side of radiator) comes on at 226-228 by the ECM. OR when the a/c is running to help the condensor eliminate heat.

The front fan (useless as lips on a wood-pecker IMO) was an add-on by dealers in response to customers freaking out over seeing a new car running at 220+ degrees and climbing in traffic. Old school mentality...new car, new technology, old school owners.
Seeing an engine running at 220 degrees was fatal in the 60's & 70's. Was hard to accept as the new normal in the late 1980's and even now.
That aux fan is there as a placebo as much as anything. It only blows a little fresh air on the condensor and helps pull a small amount of fresh air into the box where the main can get a little... The "aux" fan comes on in the 230's somewhere.
A couple things to understand that will help in this...

Fans that run without water circulating is pointless. Cooling water thats already cool does nothing for the engine temp. In fact, this can contribute to premature headgasket failures from the radical spikes/dips in temps when that cold water suddenly flows into a hot engine. Not good temp mngt. Temps need to remain stable...within 20>< degrees most times and certainly no sudden drops of 30.
A 180 or 190 stat is fine for most. Some use a 160 to let water circulate but that does not always mean the fans are running...so thats dependent on conditions and the enviroment you're in. The water flow is regulated for this reason...this is done with orifices placed in heater lines to force more water thru the other exits so cooling is controlled and so there are no "hot-spots" in heads or the block from water flowing out too quickly. It needs some resistance so the heads stay filled. Important for aluminum.

So, you need to find out what exactly was done to change your system...there are temp sensors/switches that people install, manual bypass wires, jumping the relay, different prom setting, all kinds of ways of "tricking" the fans to run when they really do not need to. The Corvette only needs a fan when its sitting still. When its moving its designed to suck sufficient air thru the nose for cooling. Fans should shut off when the car stays in motion. It is an efficient system when everything works as it was designed.

1st, look at the fan relays and see if there is some non-factory wiring there. Look for a jumper wire thats been installed. Then look for any odd switches..maybe under the hood, maybe under the dash...in the console. Look at the fan switch/sensors. These fans operate on the grounds as does every other device on a vette. Power is always present, so the ECM or some switch simply completes the ground to operate or control the device, in this case the fan motor.

If you cannot locate and "home engineering" in the wiring under the hood, then its a safe assumption that the prom or "chip" is aftermarket and has a different program than stock. Easy enough to fix. Find a stock chip, install and THEN you can decide where and 2when you want the fan(s) to operate.

FWIW, the best investment that you will EVER make while being a Corvette owner that might deal with things of this nature, would be a FSM set. Not Chitlens manuals, Not a haynes manual...a REAL FSM from GM. There are used sets on fleabay for $75 and new offered in paper or CD for around $100+. The wiring diagrams are exact and the detail is priceless. Step by step diagnostic proceedure for everything.

Good luck and enjoy your car !

 

Thanks for the info so far guys. I pulled the ecm not long after I got the car and it still has the stock chip in it. I haven't verified yet if the main fun comes on early as well. I've gone by just the sound of the aux fan that I can always hear running. Looks like my next step is to look for modifications.

Scott

 

Remove the connector from temp switch in driver side head and see what temp the main fan comes on.
Someone has probably tied that switch to both fan relays.

 

Another popular mod is to install one of the many lower temp aftermarket switches to run the wimpy Aux fan (only ) at a lower temp

If you get the FSM as recommended above you get nice circuit diagrams like this to make fault finding easy
From the diagram below ,you can see as noted by Agent86; if the two green / white control wires from the relays are connected together then both fans will run off the temp switch in the head

 

I found the main temp switch and at the other end a blade connector was connected to a tap inside a wire harness. I had pulled that blade connector and the fan in front of the car came on at 180 like usual. When I have time i'll be l digging into this further...

Scott

 

You desparately need the FSM drawings so you can see whats been done to what.
It involves a green wire...I know that much for certain ! If a green wire is somehow jumped to ground...that runs the fan whenever that power source is ON.

Look at the aux fan relay on or near the radiator shroud, driver side, right next to the headlite. It may be mounted to the shroud, or down in the front of the shroud toward the headlite. Its a relay, that will have a 2 wire set running to the aux fan. See whats been re-engineered there. If nothing then I;d say someone stuck a low temp switch in the block.

 

Did the connector on switch look like this ?






Was there just one wire connected to it?
Was this switch in Drivers side head ?

Seems odd if the chip is stock and the temp switch is disconnected, that the aux fan came on at 180*

Have you checked to see if it is only the aux fan coming on ?

 

I was thinkin that someone installed an adjustable fan switch somewhere under the hood. Probably close to the relays, by the shroud or the battery/wheel well.

Look for a small box, possibly with a potentiameter screw or dial that is used to adjust the fans start temp,. if thats it, there should also be some temp sensor or probe thats independent of the harness. That will be inserted into the radiator fins or mounted so it contacts the radiator somewhere, somehow.

there is so much "stuff" under the hood of a C4 that unless a guy was very familiar with the layout...he'd likely miss the aftermarket bolt on things..

 

I haven't had a chance to dig into this further yet. I'll let you know what I find when I do.

Scott