Ed Jean's 1981 Camaro Z-28

I use a Griffin 28”x19” 2-row aluminum radiator with a Flex-a-lite #210 dual 12" electric fan unit (rated at 2500 cfm). Instead of using the included control box with built-in bulb type sensor; I use a separate threaded type thermostatic switch from Derale (Part No. 16749). I originally had a home made control system installed (see below), but later found a Derale adjustable unit for $40 at Summit Racing. It includes the relay and AC input that can be used to wire a toggle switch. Since the Derale sensor had an extended probe, I could not install it under the T-stat like with the previous Nissan sensor (see top left picture). I installed it in a new T-stat housing (Trans-Dapt Performance Products #9468) that has a 1/2" NPT opening. I use anti-seize on the sensor threads to help ensure a good ground connection for a more accurate reading. I have the new sensor set to activate the fans around 205* F.

The following T-Stat housing corroded and developed two small pin holes that leaked more coolant than one might imagine. I had another one laying around, so I used it until I can come up with something better. Not having a new O-ring is not an issue, for I use Permatex grey for this application.

By using a thermostatic switch and relay(s) from a local parts store, you can save money over most aftermarket kits. I do not like the bulb type sensor that must be slipped inside the upper radiator hose. While breaking in a new camshaft, I had a near miss when the upper hose slipped off the rubber wedge used to help seal the bulb wire at the radiator hose inlet and hot coolant almost hit me in the upper body and face. Some coolant made its way into the throttle body and shut the motor off after only 15 minutes of break-in.

Anyway, below is an economical and dependable way to build your own automatic electric fan control system. Keep in mind that this system can also work with any fan(s) that does not come with a control box like the Flex-a-lite #210 unit. Just run a 30-amp relay(s), in-line fuse(s) and a thermostatic switch. If you do not want to spend $60+ for an aftermarket kit (like Painless with one relay, sensor, wire, etc.), here's what you do:
Relays and Switches:

Buy a relay(s) from a local parts store and a thermostatic control switch from Carquest. Pep Boys carries "Pilot" relays for about $5 each. Note: most electric fan companies recommend running two relays with separate battery feeds when using two fans. Even if two relays are used, the same signal wire can be split and activate both relays. Go to Carquest and ask to look through their Temperature Control Products catalog. Look for a fan switch that is normally "open" that most closely matches the on-off range you want. Here are some available temperature range options with January 2003 prices in Columbia, SC:

If you want a switch that comes on and turns off at lower temperatures, below are some options that can be purchased at Summit or Jegs. However, please keep in mind one thing when choosing lower on-off temperatures. Just because you run a 160* or 180* T-stat does not mean you will run that cool. Once your T-stat opens, it will only run as cool as the entire system permits. If you pick a switch that shuts off at a low temperature, your fan my not turn off during highway operation.

Because I run the Edelbrock Pro-Flo fuel injection on my 383 small block, I prefer slightly warmer operating temperatures. Accordingly, I run a 180* T-stat, and use Carquest thermostatic switch part #207454 that closes at 197* (turns the fan on) and re-opens at 188* (turns the fan off). This switch came in 88-97 Nissans and uses 3/8" NPT. By the time I get up to highway speeds, my engine runs between 180*-185*, depending on the ambient air temperature and since the switch turns off at 188*, my fans turn off at highway speeds.

Since my AFR 195cc heads did not come with a threaded opening and my Pro-Flo intake uses the only threaded port for the computer water temperature sensor, I drilled and tapped the intake under the thermostat. I also drilled and tapped this area for my electric temperature gauge sending unit. If you do this, PLEASE USE CAUTION! – be sure to drill and tap as low as possible. Your thermostat most likely drops as it opens, and a Mr. Gasket type thermostat; has a large diameter that opens between 3/16" to 1/4". When fully open, it may hit the inserted sensor if not located low enough.

Heat up the T-stat in a pan of water on the stove to its stamped rating and measure the fully opened height from the flange edge to the bottom edge. Then check the fully open height against where you drill and tap your sensor. Although most of the sensors I listed above are not very deep when screwed into an opening, it still important to verify that the T-stat can fully open if you drill and tap in the front of the intake like I did. Since the front of the intake does not have a flat surface for the sensor O-ring to seat against, I used Permatex Gasket Maker that sealed the threads just fine. Another option would be to use an OEM type water neck such as Trans-Dapt Performance Products #9468. It has one 1/2" NPT opening cast in. This will give you a good flat surface to mount a sensor or switch. I would not recommend installing your temperature gauge sending unit in the water neck since you may not notice a bad T-stat. If he T-stat went bad, how will the gauge sending unit read the overheating temperature when the coolant is stuck on the engine side of the T-stat?

Battery & Signal Power: Run full battery power from the starter solenoid or alternator "Battery" terminal to the relay with 10 ga. wire and an inline 30 amp fuse, then out from the relay to the fan's positive terminal with 10 ga. wire. Run a +12v wire (14-16 ga.) from an ignition source to the thermostatic switch, then to the relay's signal spade. Relays pull very low amps so big gauge wire is not needed for the signal function. You will also have to ground the relay. The relay has a wiring diagram stamped on its side so you will know which spades to hook up the four wires to. Since the relay spades are so close together, either wrap the female terminal connectors with electrical tape or use shrink wrap.

Alternate Battery Power Method: Run an 8 ga. wire from the alternator “Battery” terminal to a junction block or fuse block near the driver’s side headlight. Then run a 10 ga. wire from the J-block or fuse block to the relay(s). If you use this method, you can also run your headlights on relays (one for low beams, and one for high beams). Using headlight relays is an awesome upgrade. I choose to use the fuse block method (the one in the photo at the right is a Bussman 15600-06-20 [click here for a catalog picture] and came from Advance Auto Parts), but an economical and safe way to do your lights and/or fans is with a J-block and either in-line fuses or fusible links. By running your fans and lights with relays, you will have less voltage drop and a better performing electrical system.

This is also very helpful at idle when using underdrive pulleys. If you want to use the J-block method, please visit www.madelectrical.com. This is an excellent automotive electrical solutions company. Since there are many ways to set up an electrical system, please take the time to read all the various sections of their catalog and technical sections.

Conclusion: Whatever method you use, a homemade system works well, is dependable, and since it is wired to an ignition source from the fuse panel, you will not have to remember to turn it on. Just for piece of mind, I wired a small LED amber light (Radio Shack) in the dash. Run a 14-16 gauge wire from the LED light spliced into the 10 ga. wire between the relay and fan. As you watch the temperature climbing, you will know exactly when (if) the fan comes on. Since I never throw away scraps of wire, I had enough lying around to do the entire installation. Even if I had to buy the wire and solderless connectors, I would have only spent about $35. Bottom line, go automatic and save money while you do it!

Disclaimer Note – All information contained within this article was compiled using various resources. Anyone who implements or incorporates these modifications does so with the understanding that the author cannot and will not guarantee that such modifications will work exactly as described with my vehicle. This is due to many variables that only the end user of another vehicle can control. Therefore, please use this information at your own risk.

Cooling System