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.
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.
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).
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.
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.