By Chris Petris
Illustration by Chris Petris
A common question asked among C4 Corvette owners is “why does my engine run so hot? The cooling fans do not come on until the coolant temperature is way too hot”.
Federal regulations required high operating temperatures to keep idle emissions at their designated levels. The oxygen sensor works more efficiently at high exhaust temperatures promoting less fuel usage and emissions. For this reason, we recommend using a minimum 180 degree thermostat and turning on the cooling fans at the 200-205 degree range. 1984 Corvettes will have the most noticeable improvement, as the factory cooling fan setting is 238 degrees. Lower temperatures will work at the expense of fuel mileage.
There are various cooling fan control switches available to turn the cooling fans on earlier than the factory ECM or PCM controlled settings. We recommend using a cooling fan switch that matches the thermostat opening temperature. For instance, our 244455 fan switch turns the fan on in the 200 degree range. When the engine coolant temperature drops below 185 degrees, the cooling fan is turned off. Installing our 243108 thermostat allows the engine to run in the 185-192 degree range. Don’t forget the 242135 thermostat gasket to properly seal the thermostat housing.
Another scenario would be the use of a 195 degree thermostat with the 244455 switch. The fan would run almost constantly as the thermostat regulates the temperature at 195 degrees.
For lower operating temperatures, our 243139 Hyper-Tech Power Stat coupled with our 244381 cooling fan switch (that activates the fan at 185 degrees) would provide the correct hysteresis.
Have a Corvette that sees track time on a regular basis? Our 244502 (1984-93) or 244503 (1994-95) manually operated switch allows you to override the automatic switch for additional cooling while waiting in the staging area.
“Why not run the cooling fans continuously?”
Radiator cooling fans were not designed for continuous use and they will fail prematurely.
INSTALLATION NOTES
All of the aftermarket cooling fan switches have harnesses provided to connect the new style connector.
GM had a B4P cooling system option available for 1985-1989 Corvettes. This option consisted of an extra cooling fan in front of the a/c condenser, heavy duty radiator and oil cooler. We have had both the heavy duty and standard duty radiators out of the 1985-89 models and could not see any major differences. 1990+ Corvettes have two radiator cooling fans. 1990-1991 Corvettes also may have an oil cooler. 1992-1996 Corvettes do not have oil coolers due to clearance issues when the catalytic converters were moved close to the oil filter.
1990-1995 Corvettes will have a quad driver code set (16). The code will be seen while using a computer scanner but will not turn on the SES light. This code will not will not affect engine performance in any way.
1996 Corvettes will have an SES light illuminate when the fan switch is installed due to the PCM noticing the fan operating when it should not be. This will not affect engine operation or cause any problem.
1984 COOLING FAN SWITCH INSTALLATION
The 1984 Corvette has a standalone cooling fan control circuit. The switch is connected directly to the cooling fan relay without any engine computer intervention. The cooling fan switch is located in the passenger side cylinder head between cylinders number six and eight spark plugs. Use the supplied harness to connect the new style connector to the fan switch.
1985-1989 COOLING FAN SWITCH INSTALLATION
1985-1989 AUXILIARY FAN WIRING INSTRUCTIONS
1990-1996 COOLANT FAN SWITCH INSTALLATION
1985-1996 Corvette Low Temp Cooling Fan Control Switch would be installed in this location (driver’s side cylinder head between cylinders 1 and 3).
Wiring Instructions:
1985-1989 B4P Option equipped Corvettes
Cut the dark green /white wire at the inner fender well. Connect one of the new harness wires to the dark green/white wire. Route the other harness wire to the main fan relay (near the battery). Locate the dark green/white wire at the relay connector. This will make both cooling fans come on simultaneously, meaning less run time for both fans if the cooling system is in good condition.
1985-1989 Non B4P Optioned Corvettes
Route the cooling fan harness dark green or blue wire to the main fan relay (near the battery). Locate the dark green/white striped wire at the relay connector. Splice the new section of either the blue or green wire to the main fan dark green/white striped wire. If you prefer, you can connect both of the blue and green wires together.
1990-1996 COOLANT SWITCH INSTALLATION
1985-1989 NON B4P OPTIONED CORVETTES
1985-1996 Corvette Cylinder Head Plug Removal/ Switch Installation
BEWARE OF HOT COOLANT!! Drain the coolant at the radiator petcock. The radiator petcock is located on the passenger side of the radiator below the lower radiator hose.
Remove the 5/16″ square recessed pipe plug between spark plugs one and three on the drivers side of the engine. This can be very difficult. We suggest heating the area with a propane torch, then applying wax to the plug and surrounding area to help loosen the plug. To avoid cylinder head damage, do not use an acetylene torch. Before the plug begins rounding out, stop and reapply the heat and wax.
Once the plug is removed, install the new switch. This switch relies on the cylinder head for a ground circuit. Apply a small amount of sealer to ensure a good ground.
Wiring Instructions
Connect the new harness to the switch and route the leads over to the fan relays mounted on the radiator housing. The cooling fan relays are mounted on the driver side of the radiator housing. 1990-1993 Corvettes have two relays: a primary and a secondary. 1994-1996 have three relays: primary, secondary and one relay for half speed fan operation.
1990-1993 Corvettes will have the dark green or blue wire spliced into the fan relay with the dark green/white striped wire for primary fan control. This works best for stock or mildly modified engines.
Highly modified engines work best when both of the fans come on simultaneously. Splice the dark green wire from the new harness to the dark green/white striped wire at the primary relay. Splice the dark blue wire from the new fan switch harness to the secondary relay with the dark blue/white striped wire.
1994-1996 Corvettes: Locate the relays with four wires (one relay has five wires for half speed operation). Splice the dark green wire from the new harness to the relay with the dark green wire for primary fan operation.
Highly modified engines work best when both of the fans come on simultaneously. Splice the dark green wire from the new harness to the dark green wire at the primary relay. Splice the dark blue wire from the new fan switch harness to the secondary relay with the dark blue wire. There will be no wires spliced to the five wire relay.
91 corvette , My fans work by passed and tested, swapped and changed fan relays and still won’t turn on, relays are getting power 12V+. They won’t turn on. Themp control in intake changed 3 times, ACdelco and others and won’t turn on……WTF?
The turn-on temperature if you have a factory sensor is 239 degrees F.
The fans get their power from the fan relay.
The relay is controlled by the ECM which receives the information about coolant temperature from the coolant temperature sensor.
When the coolant reaches ~239 degrees, the ECM grounds the relay which in turn powers the cooling fan(s).
Thank You,
Product Assistance
I just put 2 new fan motors in my 90 zr1 and the primary fan still doesn’t come on. I switched the connections at the fan relays and the secondary comes on and still no primary who h I believe rules out the fuseable link . What now ???
92 LT1, to resolve over heating issues, we installed new factory oem Thermostat 185, removed knock sensors flushed with distilled water till clear and replaced coolant, install new AC Delco temp sensor on water pump, new surge tank due to crack in top brass and low coolant switch connector corrosion, new 15 lb surge tank cap. Both fans work with AB jumper test. Only AC fan passenger side come on with AC. Primary driver side never comes on engine over heating at 280 idling. Over heated 3 time bad hopefully head were not hurt.
Mine comes in at 236 since I changed the sensor switch at the water pump. Used to come on at 228.
Great info. Could you send me a magazine or keep me informed. purchased a 1984 .
You can check out our online catalogs here and request a paper one. We are working on the C4 catalog at this time and if you request a catalog you will be on the list to receive a new one. Thank You, Corvette Central
sounds like you have trapped air in the system. have you blead it properly? also verify ignition timing as others said. did you have the computer chip changed to reflect the lower thermostat and fan operating temps?
these cars are set to advance timing when the engine is cold. so you cannot simply use a lower temp thermostat, and bigger fans. you have to tell the computer that you are now commanding the fans on at the lower temp, and you may have to make some other fueling and timing adjustments. most tuners can rectify this for you via a mail order chip. I would speak to Scott Hansen. he is great at doing the chips for these old cars on mild street stuff.
Thanks for responding. Ignition timing is set at 8 deg before TDC. When idling at 210 deg the fan is on because it comes on at 195 deg and it stays on continuously and them OE fans and shrouds are in place. The OE pusher fan is on a 235 deg switch, when this fan comes on I both fans running continuously. I’ve purged the cooling system of all air pockets. As I stated in my opening, this setup is basically the same as a 1969 (think old school), except the fans are electric instead of clutch driven. It’s a 350 engine with HEI ignition, instead of point and condenser, carb and headers. The fans do come on at the proper times. I did call the manufacture of the radiator and I was told they have never had an issue with their radiators like this before. The radiator is aluminum with 2 rows of 1 inch tubes. It must be something else causing the problem. I bypassed the heater core and still the issue exists.
Thought: Is it possible that the (Weiand Action Plus intake) could be causing this issue? Even though it bolts up, are the cooling ports compatible? I didn’t buy the intake, it was with the care when I purchased it so I assumed it was correct.
I want to purchase what I need, but I don’t want to spend anymore more money until I know exactly what I need.
Hi all! I have done a lot of research and work on the cooling system for my 1985 Corvette. I have modified the controls for the cooling system and the engine. Sent the engine to the machine shop for a complete rebuild. New aluminum radiator (suppose to cool up to 800hp), water pump, hoses, 15lb cap and reverted it back to carburetor (Holley 600). I installed an 180 deg stat and a fan switch that turns the primary fan on at 195, off at 180 deg using a 50/50 mix of green antifreeze. I can’t get the temp to stay below 260 degrees and I’m very concerned. No more computer controlled fan or A/C pressure controlled. The engine will idle at 210 deg. As soon as I take it on the road the temp shoots up to 260 deg. Then when I get it back to home base the cooling system sounds like it regurgitating. I don’t drive it far and rarely because of this issue. I have never had an issue like this before and it’s very weird. If someone could help me figure this out with suggestions I will be forever grateful. I am at wits end!
The first thing I would do is to confirm correct ignition timing – retarded timing will cause excessive heat.
Your fan switch – on at 195, off at 180.
If you are idling at 210, then the fan is running continuously correct?
Once you are above about 30 MPH air is being forced through the radiator.
Plenty of airflow through the radiator is key to engine cooling – I assume you have all factory shrouding in place?
Have you called the manufacturer of the radiator to get their input?
Regards,
Gus
Corvette Central Product Assistance
Thanks for responding. Ignition timing is set at 8 deg before TDC. When idling at 210 deg the fan is on because it comes on at 195 deg and it stays on continuously and them OE fans and shrouds are in place. The OE pusher fan is on a 235 deg switch, when this fan comes on I both fans running continuously. I’ve purged the cooling system of all air pockets. As I stated in my opening, this setup is basically the same as a 1969 (think old school), except the fans are electric instead of clutch driven. It’s a 350 engine with HEI ignition, instead of point and condenser, carb and headers. The fans do come on at the proper times. I did call the manufacture of the radiator and I was told they have never had an issue with their radiators like this before. It must be something else causing the problem. I bypassed the heater core and still the issue exists.
Thought: Is it possible that the (Weiand Action Plus intake) could be causing this issue? Even though it bolts up, are the cooling ports compatible? I didn’t buy the intake, it was with the care when I purchased it so I assumed it was correct.
I assume if the Weiand intake is for, and bolted to, your small block, then it is not the source of your problem.
BUT the only way to definitely exclude it from the list of possible culprits is to either remove it and check the passages or contact Weiand for their input.
Regards,
Gus
Corvette Central Product Assistance
Hi Ed! I had a very similar problem and found that the coolant overflow hose was restricted and not allowing coolant to drawn back into the system. Have you checked your radiator cap.
Hi
I am planning to get the direct replacement fit lower temperature coolant fan switch (180 F).
I wonder if you can help me locate it in my 1991 lt5 zr1.
Best regard
i have a 1996 corvette collectors series my cooling fan does not come on until i turn the AC on then the temp gauge will come down, how can i get the fan to com,e on with out turning the AC on. plus under the dash on the passengers side witch relay is the temp fan relay there is five of them under there let me know witch relay i can replace, this car has only 51,000 miles on it thanks merrill
having same problem what did you do too fix it thanks
Dropping computer need oil mechanical connection & is there switch for fan, also small heater hose on AC hosting? I think it connected to intake water port. No more cross fire carb motor now. Any help would be great.
Hello, I have a 1988 corvette and just replaced the water pump, and I did not put back the big heavy round frisbee to the water pump, I plan to install a clutch fan and fan blade for continuous air cooling. Will this work? Thank you! Joey
I have never heard of anyone running a fan clutch on a C4. There are plenty of options for either turning the electric factory fan on sooner, or upgrading the fan, so this isn’t something we really get any request for. You would also want to consider that the fan clutch is not designed for continuous cooling, and the 1988 water pump is a “reverse flow”. I don’t believe this setup would work.
87 corvette cooling fan constantly on – would this be caused by the cooling fan temp switch?
I have an 87 Corvette engine installed in a 74 260Z and am using the Vette ECM with hopefully all the stock controls except for an aftermarket performance chip (mainly to help override the anti-theft control and no smog). I recently found that the fan was running all the time and can’t seem to find out why. I would also like to have it operate at a lower temp as long as the general function is not adversely affected. I’m also running the stock 195 thermostat. This is my baby so I don’t mind investing in extra devices (read cost) if it makes it RIGHT. Thanking you in advance.
I have an ’86 stock Corvette. While in a parade on a hot day going to slow for a vette my car stopped working and I had to be pushed off to the side. To me it seemed to a vapor lock. My husband who was not with me is not sure if it just got too hot and oil pressure dropped. It vapor lock once before of course I was alone. It only restarted after lifting the hood and removing the gas cap. What is your recommendation to avoid this problem from happening again. I do like taking small trips on my own and on a rare occasion I go the the local Corvette Club. I would prefer this not to happen again.
If the tank sent a big whoosh of air as you loosened it, its the charcoal canister purge system(too late arent I?), could be blocked, or the solenoid not working. In the heat, gas becomes a vapor in the small tank baking in the sun.
I have an 84 with a single cooling fan. As many others I am having problems with overheating. I installed an aluminum 3 row radiator, 195_180 switch kit from C C. At freeway speeds it runs at 195_220. In stop and go traffic it goes up to high 240s to as high as low 250s. As I stated I installed a 3 row aluminum radiator, a 195!180 fan switch, a new sensor in the front of the engine intAke manifold, a new sensor between plugs 1 and 3, and the fan relay. It has a 185 thermostat. ????? Next step ? I have 2 new 10 inch fans I aS thinking of installing but can’t find kit or wiring diagram for adding a second fan for my 84. Help ! Even with the stock fan running constantly I can’t drive my Vette in traffic. I live in Vegas so the outside temp in summer is 105 to 115. My Vette doesn’t have a chance. Do you think pulling the stock fan and shroud and I stalling the 2 10 inches will help ? T Y in advance for any help or suggestions s.
Your corvette have a performance camshaft or stock? if your corevette has a performance camshaft you must make a deegre to the time.
1985 Corvette with B4P option with new 195 degree fan switch.
I want both fans to turn on together at 195 degrees.
I ran one harness wire to the green/white wire at main fan relay and spliced in. Perfect, main fan works.
I cannot get the auxiliary fan to come on.
I routed the second harness wire to the green/white striped wire at the auxiliary fan relay and spliced in but, nothing. I must be doing something wrong, please advise.
Thank you
Rick, it is not a good idea to run both fans because the secondary fan is a ball bearing type of fan and it would fail on you. The primary fan gets its signal from the Computer via of the temp switch by No.1 Spark Plug. You can install a retrofit kit from Corvette Central that would bring your Primary Fan on at about 200° on and 185°off. This is the best and safest way to go.
I have an stock 84 corvette. I’ve installed a 180 Hi-flow thermostat, 180 degree sensor and 3 core Radiator. When I first start it, the car temperature goes all the way up to 240 before it starts to cool off. Any idea what could be the problem?
Are you still running the factory fan switch? Do you know at what temp your fans are coming on? From the factory the fans are suppose to turn on at 230 degrees. Here’s a low temp fan switch we recommend https://https://www.corvettecentral.com/search?CurrentSearchCategoryId=&q=244074
I just put a new switch in my 84 and it does the same thing, comes on at about 235F. Apparently this is normal
89 corvette primary cooling system only just bought mini project car noticed broken conector for fan switch car s fan comes on 228 .flushed cooling system changed thermostat 180 want to get all fluid out block and same time lower fan switch temp to 200.whats pros and cons to doing that? need proper wiring directions also will removal of switch drain coolant in block. drained raidiator several times
The stock C4 Corvette cooling system runs inherently hot. We offer electric cooling fan switches in four different temperature ranges. The switches will turn on the main fan, auxiliary fan or both at a lower temperature. Lower coolant temperatures will maximize engine performance and reduce engine wear. Each kit comes complete with switch, harness, hardware and instructions for easy installation. https://https://www.corvettecentral.com/search?CurrentSearchCategoryId=C4&q=cooling+fan+switch
just bought 89 two, questions one noticed broken temp coolant fan connector , for a 228 switch just flushed system installed new 180 thermostat, interested in a 200-205 fan switch. whats the pros and cons to going down? also looking to get block completely drained will coolant drain from switch hole? also would like proper wiring procedures for new switch/ connector and wire pretty sure i have primary fan only don’t see another in front of ac.
The stock C4 Corvette cooling system runs inherently hot. We offer electric cooling fan switches in four different temperature ranges. The switches will turn on the main fan, auxiliary fan or both at a lower temperature. Lower coolant temperatures will maximize engine performance and reduce engine wear. Each kit comes complete with switch, harness, hardware and instructions for easy installation. https://https://www.corvettecentral.com/search?CurrentSearchCategoryId=C4&q=cooling+fan+switch
I have a 84 corvette and the temperature sensor for the fan needs to be replaced. I bought a sensor that turns it on 200 instead of 230 but the connection is different. The new sensor also comes with two wires but car only comes with one. Any help is appreciated.
Did you buy the sensor from Corvette Central? You can give us a call at (800) 345-4122 and we can help you get the sensor that you need.
Have a 1985 with the second fan option. I was told that the switch between cylinder 1 and 2 send info to the dash gauge, the switch between 7 and 8 operates the auxiliary fan, and the primary fan is ecm controlled. I currently have an 180 degree thermostat, would like to get one of these lower temp units but want to make sure i wire properly. Also do i need to replace the switch that controls the auxiliary fan? Which unit do you suggest with a 180 degree thermostat?
Each kit comes complete with switch, harness, hardware and instructions for easy installation.
1994 Coupe, no power to the a/c clutch plug. I found the secondary fan fuse blown and with a little testing discovered the secondary (passenger side) fan motor is toast. Anyone know if this fan is inclusive in the a/c electrical loop? I am right now ordering a fan motor from Corvettecentral.com but does anyone else think this motor replacement will fix the no power to the A/C clutch? I so love my vette
All LT-Based engines have the fan power routed through the AC pressure switch. If you do not have a full (Or at the least adequate enough to cool air from vents) charge of Freon your fans WILL NOT run. It is a horrible design. I found this out the hard way. I bought a 6spd Trans Am that some one had evacuated the Freon. Worked for days before finding out through a site called Shoebox.com that the fans do not run without enough Freon in the AC system. This site is AMAZING. Loaded with useful information for anyone who owns an LT1 engine. Check them out. I am a tip jar donor to the site. They have saved me $100s of dollars on repairs so I send a little cash their way each time they save me from paying a mechanic.
It’s shbox.com not shoebox.com
1996 corvette how to program the fans to cool to a lower temperature, the fans on my vette start at 230 degree to low speed, I think is to hot
We offer a 160 degree Hi-Flow thermostat which allows your engine to cool down to lower temperatures than the factory thermostat. 1984-1996 have a reputation of running hot from factory.
I live in Las Vegas with hot summers and would like my 93 C4 LT1 to run cooler. What cooling temp sensor and thermostat pair do you recommend to keep the car running at 200 deg or less? I am not worried about gas mileage, I just want to cool it down. It does not overheat per the specs, but these cars do run hot and cooling it down I have heard will add life to the motor.
We offer a 160 degree Hi-Flow thermostat that should help out a lot.
Do you have a low temp thermostat for an 85 Corvette?
For 1985 we offer a 160 degree low temp thermostat. Here is the link https://https://www.corvettecentral.com/search?CurrentSearchCategoryId=&q=243139
I would likexpect to order that thermostat how?
You can order at https://https://www.corvettecentral.com/search?CurrentSearchCategoryId=&q=low+temp+thermostat&Years=1985 or give us a call at (800) 345-4122
You can hold the arrows of the HVAC controls (setting 16) to allow you to see what temperature the engine is seeing. This way you know if your dash gauge is off and you can know what the temp really is. I believe at 113 Celsius the primary fan comes on. If it’s not at 113 it’s not hot enough yet (even though the gauge on the dash is saying you’re overheating. I just had a mechanic wire in a toggle switch on the ground side of my fan relay. Now with the flip of a switch I can make my primary switch go on (other fan i just use the AC to turn on).
My 1995 Corvette fan will not come on at any temperature. I hot-wired the fan and it came on. I swapped the relay switches around and it still would not come on. The fuse is not blown. Is there another switch I can check? Is there another switch running from the thermostat to the bottom of the radiator hose? Thank you for any help.
We offer an Engine Cooling Fan Switch, which will allow you to manually turn the fans on whenever you like.
I like the engine cooling fan switch send.
Does the switch allow for the automatic fans to turn on without using the switch?
Yes, the fans will still turn on at the factory specified temperature.
Gus Gustafson
Check the fuseable link from the relay to the right bottom side of the batery. Down behind the battery hold down. They sometimes go bad from heat.
Had that happen on my 91. The secondary fan was intermittent. Turned out to be a bad crimp someone (purchased the car used) had done on a terminal block by the battery.
THANKS FOR THE INFO ON THE COOLING FANS AND HOW TO INSTALL A SWITCH TO MAKE THEM RUN TOGETHER. YOU KNOW I HAVE A CHILTON MANUAL AND NEVER Address the second fan.
I have a 1996 vette the cooling fans will not come on at any temp but turn ac and they will work. for right now that how i have too drive the car with ac on that hold the temp at 205 deg but with out ac on the fans never come on. help
Unfortunately, we do not currently offer a manual override switch for the engine cooling fan. You may want to have a mechanic investigate further.
Check power to your relay, and if no power, check the fuseable link from relay to the battery block located ight side of battery down bahind the battery hold. Bolt.
What was the problem? My 1996 c4 corvette is doing the same exact thing!
The fans electrical is routed through the HVAC pressure switch on all LT-Based engines. It is a HORRIBLE design. The fans WILL NOT run without adequate Freon in the AC System. Basically the car must be blowing cool (At least) air through the vents before the engine fans will come on. It also controls the AC clutch activation as well. So if you have no power at your AC switch at the compressor & fans; PUT A COUPLE OF CANS OF AC PRO in the low side AC port. Once the correct pressure level is reached the fans & AC clutch will both come on. I KNOW this to be true as I JUST did this with my 1996 Corvette. It solved my issue.