Adding electric fans to an antique car

Hello all,

I have a '71 Pontiac station wagon. A while back I sent my POA to be reconfigured for 134, changed to a parallel flow condenser and added a Pro 6 Ten compressor. The car would run hot (455 bored .60 may be the problem) when the A/C was turned on, but never ran hot otherwise. I would like to change the mechanical fan on the engine to an electric puller fan. I'll make my own shroud. I believe the correct operation of this fan should be that it comes on only when a particular temperature has been reached. I would also like to add a pusher fan in front of the rad/condenser. I believe the operation of this fan should be that it comes on any time the A/C is turned on. This car, of course, has no computer.

Is my assessment of when and how the fans should operate correct? I am unaware of how to wire and make this setup operational and would appreciate instruction. Here is a small picture to help visualize my desired physical setup.

Thank you,
Brandon

 

The old Pontiacs were known to run a little warm. Add .060 to bore and now a little warmer yet. I would suggest going with aluminum 3 -row radiator with one electric fan. you will gain horses and run allot cooler. Cooling systems have come along way since the 70's I'm a hardheaded old man and now in the past couple years will swear by the extra cooling of aluminum radiators. Wish that I had one when I had my 67 GTO because keeping it's engine cool was always a problem.

 

I don't remember exactly how they were wired, but I remember troubleshooting a few non-computer cars.

There was a temperature switch mounted in a bung in the radiator. It operated at a specific temperature and activated a relay which turned the fan on. When the temp fell below the specified temp, the fan shut off. It was also wired into the AC circuit such that when the AC was turned on, the cooling fan was too.

I also just remembered that there were aftermarket fans which included everything needed for installation as well as a wiring diagram.

 

There are now stand-alone controllers, configured to run one or two fans, A/C or not. The early FWD cars had the sensor in the t-stat housing, while RWD cars had them in the radiator. But whichever way you pick up the temp, the controller switches the fan or fans on, low or high speed, and cycle the fan on high at the same time the compressor clutch cycles on. It carries the fuses for circuit protection and the plug for the system wiring.

 

Didn't like the answers you got over at hotrodders.com? Same answer here - the mechanical clutch fan will move more air than the electric. Fix the real problem, don't band-aid it.

 

I put a dual electric fans with the custom shroud looked real pretty but on the highway with the a/c on the car would overheat. The fans were actually restricting the flow put the mechanical fan back on and no more. Overheating plus old cars just don't sound right with an electric fan

 

If your engine is bored out +.60 instead of +.060 saying it "may be the problem" is right.
There are no cylinder walls.

 

Haha, you're right, I bored them so far they're actually all one cylinder now on each side.

It's not that I didn't like the answer I got at hodrodders, it's that I posted the same question on numerous forums because you never know who's going to read what you wrote and it's always wise to get as many opinions as possible. As far as mechanical fans moving more air, I agree, but using an electric fan is not a "band-aid." There are numerous reasons why an electric fan may be beneficial to a mechanical fan. Moving more air is a general term and does not specify at what conditions it moves more air. At idle, at highway speeds, when towing trailers. What about parasitic loss of a mechanical fan versus the loss of a thermostatically controlled electric fan(s). Can a mechanical fan compensate for the modifications from stock I've made to this setup? Just moving more air is not enough. There is a correlation between how much more work is involved it takes to move more air and how much heat and loss is created in producing that extra air, and when that extra air is applied versus the versatility of electric fans being able to apply specific amounts of air, at specific points in a system, when and where it is needed. These are all things I want to learn, know and understand and an explanation of "more is better" isn't going to do anything for my understanding of the situation other than having a setup that "some guy on the internet told me to."

 

Well one thing that's apparent is that there's some misunderstanding as far as how an electric setup's designed. This may have come from hot rodders and drag racers stuffing ever bigger engines into the same engine compartment, and not having room for a fan. In our part-throttle driving, we need the setup to pull the air through the radiator, and do so in keeping a higher-pressure area behind the core, which allows more heat transfer. Once the air leaves the shrouding, it loses heat by losing the built-up pressure.
Now, cooling fans are designed to move as much air as possible at the 12 volts the electrical system provides without overtaxing the alternator, battery and wiring. There is no problem in placing a single fan for small-displacement engines and dual fans for large-displacement ones. You just have to make sure the electrical system will handle the extra amperage loads without breaking/melting down. When it comes time to uprate Babe's engine and install replacement A/C, I will be installing a Windstar dual fan unit, controller and at least a 95 amp (or 130 amp, if I need it more) 3G alternator. Doing the SEFI means I will be upgrading the harness and grounds.

 

Um... How, exactly, does the radiator know if you are pulling or pushing the air through it? All the radiator knows is that it is rejecting heat to an airflow that is moving a certain number of CFM. Yes, airflow through the radiator must be able to also exit the engine compartment, but that's a function of outlet area, not whether the fan pushes or pulls.

Personally, I'm not enamored with an electric fan that bolts right to the front of the radiator. It's more of a blockage than a flow promoter, especially if used in conjunction with a mechanical fan. The fact remains that these cars did not overheat from the factory, and changing to R134 doesn't change the amount of heat rejected through the condenser (heck, the less efficient R134 probably REDUCES the heat in the condenser).

Personally, I'd start by looking at timing and mixture ratio. Keep in mind that ethanol-mixed gas causes lean conditions. Have you changed jetting to accommodate? Is the timing using ported or manifold vacuum for advance? If ported, do you have a thermal vacuum switch to change to straight manifold vacuum if the engine overheats, as was used by the factory?

 

You mentioning not putting the fan in front of the radiator is part of the point I was making: the reason why nearly all fans are behind the radiator, whether electrical or mechanical. And yes, there are factors of the radiator install, including the shroud, that affect the rate at which a radiator will shed heat. Although, I will admit, you do have valid points about ethanol and the timing/timing vacuum source. Anyway, good and bad cases can be made for both mechanical and electrical fans. Since Babe has not had her original engine and trans since I pulled them, I can set up either way. Right now, I have an HD clutch with a 7-blade fan, and a brass radiator. The radiator would need rodding out from sitting for so long, so I'm going to try an aluminum '90 5.0L radiator and shroud to see if they will work as efficiently as the brass one when I go to flush the cooling system and make a couple repairs.

 

Actually, they aren't. Obviously a mechanical fan needs to be on the engine (which can be either in front of or behind the radiator, depending on which end of the car it's in), but electrics can go either way on modern cars. I think the "behind the radiator" is more common on production cars more for access for servicing and/or for ease of assembly line installation than for any other reason.

 

I'll also point out that my 1999 Chevy truck came from the factory with both a mechanical fan, and a front-mounted electric.

 

The front-mounted electric is for the A/C only, IIRC; I've seen many Euro cars set up that way, but my bro's '97 Grand Marq, as well as late-model Grand Cherokees, have an electric fan Incorporated into the shroud, likely for the reason you stated, ease of assembly. But as newer vehicles have come out, the mechanical fan has disappeared in favor of the electric fans on RWD/4WD vehicles.

 

This is a function of meeting CAFE limits. The automakers are scrambling for every fraction of an MPG. Electric fans can be controlled by the ECU to minimize draw on the system. Same thing with alternators where the ECU controls output to minimize drag on the engine, or 8, 9, and now 10 speed transmissions. Don't confuse these games (which are primarily aimed at maximizing mileage on the EPA test cycle) with cooling efficiency.