wheatpj

I replaced a fabricated aluminum radiator installed by the prior owner with a DeWitts Direct Fit Radiator and SPAL Dual Fan Condo setup. The old fabricated radiator did a good job cooling but was a really eyesore in the engine compartment. The new DeWitts radiator is installed and looks great. The question I have is how to bring power to the fans. The prior owner used a single 16 inch SPAL fan. He powered the fan from an electrical junction block that appears to be OEM (see photo). Note the red wire coming off the junction block to the fan relay. I could follow the prior owner by removing his wire from post on the junction block and install two wires to power my fans. However, I am reluctant to do so because I am uncertain whether the OEM electrical junction can handle the combined amperage of the two fans. The direction show getting the power from the positive terminal of the battery, but this isn’t practical for our C3 Vettes. It seems most use the positive terminal on the alternator. I could run a wire from the positive post on the alternator to a newly installed electrical junction block and power my fans from the new junction block. I think I can follow the prior owner for the ignition switch connection and the thermostat. However, do I use the exiting OEM electrical junction block or install a new one? Do I get my power from the positive post on the alternator? Any advice and suggestions are appreciated.

Thanks
Pat

gmachinz

I'd suggest running the fans in series so you have a low and a high speed. You'll need to install 2 temp switches to accomplish this. You can find diagrams online for wiring it yourself....here's one of mine for use on a RamCharger fan assembly-the same type of harness (with a couple changes) will work with your Spal fans. Its a much more efficient method of running fans than simply on/off full speed all the time.

Are you still using the stock SI alternator?

terrys6t8roadster

It's always nice to know what year vette we are working on so someone can make the right suggestion. On my 69 there is a circuit breaker on the firewall, the wire from the horn relay terminal is what I used for the fuse power supply to the relay. T

rayluka

A/C or no?

toobroketoretire

On a C3 Corvette you can get the power from the top 3/8" NC lug on the starter solenoid. That is the same as going to the positive terminal of the battery. Which alternator do you have? A 37 amp or 61 amp? I recommend using at least a 61 amp because of it's greater output.

zwede

Here's what I did on my '71:

• I had the 60A alternator, upgraded to a late C3 alternator (12SI series) as they charge better at low rpm.
• I took power from the alt lug, two 14 gauge fusible links right at the lug going to a small fuse box I mounted next to the brake booster. The fuse box uses modern blade fuses.
• With ignition on the fans run at 1/4 speed (connected in series). At 210F they switch to high (parallell)
• The low/high speed switching is done with 3 relays mounted next to the fusebox.

The factory distribution block on the horn relay is iffy at best. The feed to it is small gauge, I personally wouldn't pull much juice from it. It's already taxed heavily.

wheatpj

It's a 71 Big Block. No AC.

Richard454

Another vote for the starter lug- if not running to the battery. There is a reason the Manufacturers say run it to the battery...

The battery -other than start your car -stabilizes the voltage swings.

When the fans start up- usually when in traffic-idling- the alt is not running fast enough the put out rated power-plus the fans as they start up -is almost like a direct short- takes almost 50% more current to start them spinning.

Next time you need to jump start your car- connect the jumper cable directly to the alternator and tell me how well that works for you?!


When these cars were designed 40+ years ago- the engineers had no idea the wiring would ever need to handle large current draws your are asking for now.

The other factor is heat- wire is rated for current capacity at IIRC 70º- and under the hood- it's likely to be higher!!! As the wire heats - resistance increases- as a rule of thumb w/ the higher temps you would want to move up one wire size. (down numerically)

Another trick -is run the smallest size pulley on the alt- opposite what the tuners are doing to get a few HP- spins the alt faster at idle when the fans are most likely to be needed.


As far as two speeds- I think Tom Dewiitt had some thoughts/input on another thread to this as whether or not it was that beneficial. And depending on how you wire it- adding more relays- when the fans start up in low speed- both relays are carrying full current for both fans.

I wired my Spal's - One comes on when I turn the AC on- both come on if the temp goes up. I also have the ECU turning off the fans at 35 MPH or at 70% throttle.

Upgraded the wires (10GU) and removed the connectors on the fans-I have seen several connectors either corrode or get melted- and If I have to replace the fan(s) cutting the wires is no big deal.

I have put c-clips to hold the wire in place-grounds go to the driver's side and ground on the frame- pos goes to a couple of Bosch relays disguised as a voltage regulator and weatherproofed.


DSCN5192 by Richard Hayes, on Flickr

Overkill? Why not?
1/0 to the starter- and 4gu to the upfront post to run headlights/horn/fans/electric headlight motors-

DSCN5177 by Richard Hayes, on Flickr

DSCN5169 by Richard Hayes, on Flickr

Waterproofed relay cover-

DSCN5180 by Richard Hayes, on Flickr

gmachinz

Running both fans is much more efficient in terms of total cooling than one, then the other. If you are going that far then its better to wire in series. Newer CS alternators (specifically GM spec'd ones) have a faster operating regulator which "sees" and responds to voltage fluctuations far faster than the SI alts. For that reason alone the CS swap is worth it-and running the fans in series has very little impact inrush current/wise. The worse way to power them is 100% on and off. The motors take a voltage spike hit every time which shortens their lifespan.

wheatpj

Thanks everyone for the advice.

I got the fans wired. They work great, but the alternator can’t keep up. If I pull the fuse for one of the fans it does okay and had no problem keeping cool on my test drive. I will have to replace the alternator with a higher amperage one, but that is a minor issue now. On my test drive I noticed a noise. There seems to a knock in the engine. The radiator install was the last of the (procrastinated) winter projects that included main bearing seal, harmonic balancer, and timing chain. The thought of pulling the radiator and all the work I’m going to have to do to get the front timing cover off and to drop the oil pan….when I am not so depressed, I’ll post for some thoughts and advice on the knock. In the meantime, maybe beer will help.