Radiator Cooling Fans

I’m just now getting my car back up and running after an extended hiatus to correct a number of things that needed correction. The cooling system required a major upgrade, as it was never going to function efficiently the way it was configured by the original owner/builder. There were so many things wrong with it, I’d have to write a book to cover it all.

At this point, the system has been correctly configured front to back and looks to be functioning flawlessly. The only thing that concerns me now, is that the cooling fan motors are extremely hot to the touch after only a few minutes of run time. I’ve never noticed that to be the case before. Do these fan motors normally run hot to the touch? Btw, these fans have very low hours on them, like everything else on the car, so service life wear is not a factor.

I should add, the wiring on this car is also a big mystery. Everything works, but the wiring doesn’t seem to follow recognizable color code and gauge standards of a typical commercial wire harness such as Painless or Ron Francis. I have no schematic, and all of the wiring is encased in plastic looms, so any electrical troubleshooting will be a hugh PITA.


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Howard Jones

Just to get you started. The pigtails that come out of the fans are the gauge of wire that we must assume is adequate. Since there are two of them in parallel then the feed wire to them should be at least the same gauge if fed separately back to the power source or if both are fed from one feed wire then at least about 10 gauge. See the chart below, and assume a run length of less than 10 feet and a fan current load of about 10-15 amps each. Since the run length is very short from the fans to the fuse block (I'll assume it's in the cockpit under the dash) then a 12 gauge feed wire should be good enough if that's what you have already. If you feel you need to correct this then I would go with two 12 gauges feed wires, one to each fan, back to the fuse block, or relay output.

The range of fans would be 3-5 amp fans (low power and cheap) to 15-20 amps (very powerful and expensive) The diameter of the fan also is a factor as it relates to power consumption. Gt40s typically have two 12-inch smaller diameter fans in them side by side so they are on the low end of the power scale because the short blades don't consume as much power to turn them.

Otherwise, 12.5 amp motors for example would be consuming about 150w. if they are about 80% efficient then each motor will produce about 30 watts in heat. You can't put your hand on 30 watts. How hot is yours? I would say that if you can touch it for a few seconds then it is probably ok. Especially if they remain at a relatively constant temperature. Remember, a lot of that heat is being produced by the radiator hot air flow and is normal.

Another thing is the fuse being used. You might want to see if you can find a data sheet for your fans. It should not only tell you what the power consumption is but what to use for a fuse. Generally speaking, if a motor is not making a mechanical bad bearing noise, runs at a normal speed, and not blowing fuses then it's more than likely ok.

Or the fan blade itself is being obstructed or jammed somehow by the shroud, mechanically excessively loading the motor, and drawing more than normal current.

If you find the datasheet and have a multimeter that can read amps then see what they draw on startup and at constant speed. They should be pretty close to each other in comparison and in line with the datasheet information.

last thing. When turned off does the fan blade spin easily and freely by hand? Do they both feel the same.? Both yes? Another indication they are ok.


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Ian Anderson

Lifetime Supporter
How hot is the plastic surround and the fan blades? This will be the ambient temp as everything is sitting in really hot air immediately behind the radiator

Howard, great response, very detailed as usual! The fuse panel is actually mounted above the foot box under an aluminum cover, so the wire run is only a few feet at most, with the exception of the manual switch on the instrument panel. The fans are protected by a 20 amp fuse and what appears to be 12 gauge load wire. The fans freewheel easily, they make no noise, and they flow a good amount of air. The heat they produce is enough to be concerning, but not to the point that I can’t hold my hand on them. I’m just wondering if they’ll continue to heat up further under continuous operation.

I’ve tried to locate a spec sheet, but the fans are unbranded with no info to use in a search. They look identical to other RCR fans I’ve seen on other build logs, so maybe I’ll give RCR a call to get some info.

They seem to be working fine, not blowing the fuse or melting wires, so I’m probably being overly cautious.

Ian, the plastic surrounding the motors doesn’t seem to be scary hot, just the metal motor housings.

Thx gents!
We Pantera guys run individual hot leads directly from the battery to individual fan relays avoiding the harness all together. 12G is fine for the power in and out to the fan. You can also run a similarly sourced 12v hot to the switching side of the relay such that all you need to run into the cabin is the ground side through a toggle switch to chassis ground. I use an idiot switch as I don't want the fans on thermostatic control. You can buy new SPAL fans on Amazon which are a very high quality and flow nearly 2000 CFM each. Make sure they are running the correct way depending on whether they are in front or behind the radiator :). They also sell a nice 40 amp relay and wire kit or buy just the relays on Amazon. The fans pull nearly 30+ amps at startup. This has proven to be an effective setup eliminating the fuse block and a bunch of harness wire and gives an absolute 12V to the fans. Each hot lead from the battery also has a fuse in line.
Solid advice Lee, thx

My wiring appears adequate and the motors are functioning well in spite of running hot, but I’ll spend some time with a VOM and a laser thermometer tomorrow to be on the safe side.

Howard Jones

Ya, I think you are OK. Especially if the fans run well for the next few outings and do not fail. What you want to watch for is that both fans exhibit the same symptoms. Same motor temps, same noises, same apparent fan speeds, and same current draw. There is a VERY low chance that both fans would fail at the same time or exhibit the exact same symptoms prior to failure AT THE SAME TIME. Things just don't work like that. It's not that it can't happen, But it just doesn't.

You're OK.
Just as a follow up. I checked the temp of the two fan motors with a laser gauge after running for five minutes without running the motor, neither fan showed more than 85 degrees.

Started the motor and let it get to operating temp and rechecked the fan motors, both were up around 185 degrees, so clearly they’re just picking up radiant heat.

Howard Jones

Isn't data wonderful? I had guessed that the stuff directly behind the radiator would be very near the coolant temp. Now we know.