I have a secondary fan in front of the radiator and primary fan in engine bay. What controls the secondary in front? Have not known for it to come on. There is a switch by right leg under the dash, whats it for? someone said it allows coolant fan to run all the time. Doesn't seem to do anything. Any one have an answer?

 

If it wasn't tampered with the pusher fan is controlled by a switch/sender between plugs 1 and 3 in the drivers side head. It won't come on until coolant temp reaches @ 236*. I have no idea what the switch under your dash does it is not stock.

 

Someone might have put in a switch to manually control the fan. Trace the wires from the switch and see where they go. It could also be a valet switch for an aftermarket alarm or ignition kill.

Does the main fan come on with the a/c?

 

Good to know about pusher fan and yes radiator fans starts with a/c. I have found another 87 with same switch. Good idea on wire trace

 

I have a fan bypass switch under the dash in my 87, mine is a 3 position switch.
towards the driver - no fan bypass
center position - primary fan on always
away from the driver - primary and secondary fan on always

No overheating in traffic jams.

 

very cool...my aux fan comes on at 193, I've never seen, or heard, the main fan come on, in normal driving, but I do know it works. I'm pretty sure someone put in the kit to have the aux fan come on sooner.

 

Like that idea, any info on where you got the tech for that?

 

Hello,
Having trouble with my 87, coolant fan. primary fan wont come on but the aux works as normal. I am tracing the trouble, fan motor and relay is just fine, mayb bad wire to ECM. Cause I just replaced the ECM...
wont come on with AC either...


ANYWAY

what is wrong with running the primary fan always when the engine is running? The thermostat at 195 controls the engine temp. anyway that is the way the older cars with a belt driven fan work, fan on when engine running.
SO what is wrong with that?
Anyone? any input on this would be helpful.
george
Portage, In

 

I have a question concerning, the fan, sensors, etc. on my 87 Roadster. I recently began having a Check Engine Light come and stay on....it will not allow access through the computer portal to code check, unless the computer has been cleared then all you get is the normal code 12. The engine runs good until the fan comes on at about 115 Degrees...engine falls flat on its face until the computer is cleared. Same/same....once it goes over 100 degrees, the computer goes crazy and the ENGINE refuses to run right. Any Suggestions? User..the new guy, all help would be appreciated, I have spent the last several days attempting to trouble shoot and pinpointed the problem to the cooling system and or fan relay which I have replaced with no results.

 

I would suggest it is not a cooling problem but one of the ECM "thinks" the engine is at a higher temp than it actual is and changes it's settings accordingly.
Start by replacing the $14 CTS at front of intake

http://tpiparts.net/inc/sdetail/10956/497

that sends the engine temp reading to the ECM.( seperate sensor to temp gauge sensor )
If it is reading wrong then it throws all ECM parameters out




Or at least pull CTS out and test to see if it is showing the correct ohm values at different temps
http://www.corvettebuyers.com/c4vett...nformation.htm

 

Thanks, One more sending unit can't hurt....as I have replaced the O2 Sensor, the MAF Senor, the TPS, and checked the voltage and ohms on the wiring circuit, plus replaced the relays in the cooling system....all because of the FALSE codes coming from the ECM, BEFORE I realized the computer was going crazy each and every time the primary cooling fan came on at a way to early temperature reading....I have already pulled the ECM awaiting the replacement rebuild I ordered. What I discovered was the FACT that the ECM in the CAR was a rebuilt and not a factory original...I am the 2nd owner and was under the false impression that everything was factory original.

This suggests a recurring problem....perhaps something simple as you suggested. Your input has been helpful as I did not realize that such a PART existed....according to the supposed MASTER MECHANICS I have consulted...each assuring me there was NO SENSOR that feed such information to the EMC about the cooling system. Thanks again...this knowledge could have saved me a few hundred dollars if I had possessed it earlier, and its not from a lack of research as I now Know my CAR, both mentally and physically as well as I do my wife....a KNOWLEDGE that I had no intention of ever gleaming.....but THANKS.

 

Here is some info from my 86 factory manual.

http://members.shaw.ca/corvette86/Co...%20Control.pdf

That coolant sensor usually throws a code 14 or 15. I had a 15 and it did make it run like total crap.

http://members.shaw.ca/corvette86/Code%2014.pdf

http://members.shaw.ca/corvette86/Code%2015.pdf

 

Thanks, I purchased the car for one reason.....the documented low mileage, as the CarFax verified the 31000 miles on the Odometer, originally delivered to a Callaway dealer in Fla., and had 8000 miles on it before it was titled....it was slated to get the Callaway treatment...but was sold to the public for some odd, undetermined reason, perhaps now we know why. Its history was why it was in the Auto Museum in Chicago. It came from Voloauto museum in Chicago. I have owned it a couple of years with no problem whatsoever...but its a toy that I seldom play with as its sits in the garage 95% of the time.

However the seller was less than forthcoming with the entire history as demonstrated by the fact of the ECM being a re-manufactured unit. This information will be very helpful, as I am somewhat attached to the car now....and would never think of selling her due to a few hiccups.

 

Early C4's got lot's of ECM Reman Units - there were no new replacements and there were numerous failures under warranty (I had at least 3). The alternator may also be a Reman - there's never been anything other than a rebuild for that too. I quit counting at a dozen and the Vette Mags of the day always recommended you carry a spare. Apparently it cont'd with the C5 - Car & Driver's early unit left them stranded for a week when it broke and there were no replacements of any sort early in the C5 run.

Aux Fan started as a Dealer installed option in '85 with GM's Service Bulletin describing it as a fix for overheating complaints from Auto-Crossers and High Altitude Users. Never intended for everyday use, but I have no idea how or what Callaway may have done with it.

You might want to pickup all the literature you can about your car - including the couple hundred Service Bulletins that outlined the numerous quirks that plagued a lot of the C4's. Unfortunately, some have been edited by GM, so you might not get all the juicy tidbits and lore that made the C4 what it really was.

 

One more question concerning my ignorance about the C4s....While trouble shooting the wiring I noticed a small sending unit of some kind sitting in front of the radiator, between the fan and engine....it looks something like a small Horn but clearly it is some kind of meter to measure air flow...., just curious, does anyone have any idea about this devices purpose, it has a collector about 2-3 inches in diameter? It kind'a reminds me of the collector used to measure air speed in old army rotary wing aircraft's.

 

That is the air conditioner's outside air temp sensor. The inside air temp sensor is above your head on the black halo panel that goes from side to side forward of the hatch hinge.

BTW, I tied the coil of the aux fan relay to the main fan power wire, and both of mine come on together. makes a bit of a loud fan noise, but they both are working. The aux fan cools the condenser to keep you cool, and the main fan keeps the engine cool.

 

The ECM has a " limp home" mode that allows the car to be driven if some sensor inputs to the ECM are lost.
IIRC ; the CTS input is one of the few inputs it absolutely requires to retain minimum drivability

"Failure of a CST will affect the functions of the fuel delivery, ignition timing, cooling fan, TCC and the idle control."

 

Who was the dealer and what are the last six #s of the VIN?

If I can help...

 

There was no Dealer....it was a private owner that had placed the car on consignment to the Museum, the Museum sold the car as is and I actually never meet the titled owner in person. It was a case of "Caveat Emptor". I have no complaints, the car is as advertised, I researched the Vin. before I purchased and also confirmed the maintenance record through CarFax. This is the first problem that I have encountered, and from what I understand its nothing that is not common to the Model, its not a question of ethics, its just the fact that I never actually got to talk to the former owner, perhaps the broker at the Museum was just as ignorant as I. But Thanks.

The Museum has a good reputation and does move quite a bit of Muscle and Antique autos all over the world, they screen quite well and deal only in quality merchandise. www.volocars.com

 

It seems to me the R and D folks did not consider this much if it is to measure outside air temp., where its located its got be hotter than the gates of hell when the auto is at operating speed. Just thinking out loud. But Thanks, I am no longer ignorant to this devices purpose. And.....I have a convertible roadster, there is no hatch as the top folds down under the back deck. But as I said...you addressed my ignorance, again, thanks. Perhaps this is the reason it never received the massage from Callaway, I am not sure if they converted any Roasters during those years.