I have a new rad from Ron Davis with twin fans on it. I have recently installed a new engine harness from M&H. The question I have is what would be the ideal way to wire up the fans. The fans came with the necessary harnesses and relays so that is all new as well. I have a single wire 100 amp alt with a heavy guage wire going to the batt so no problems there. The car has no A/C or power windows so the demands on the electrical system are not too high. I am running a small block with a 200R4. Should I wire it up to allow one fan to come on and off as desired and control the other manually from within the car? If so how would I do it? Should I allow them to both come on together? Should I get a controller to allow the fan to come on at half power then increase depending on the temperature?

Throw me some ideas guys because although the harness is new I am a little worried about it handling a huge draw when the fans kick on. I do a lot of city driving and I really only want to do this one time. I am NOT very comfortable with electrical at all. Basically what would be the best way to wire it up? Temp gets above 90 where I drive during the summer. Thanks for the help.

I just did this on my '71.

Twin 13" Flexalites and a relay kit from the parts store. I also run a drilled 180° T-stat.

I use a battery that has both top and side posts with the side posts used for the car and the top posts used for accessories. That's where I have the main power to the fan relay tapped.

This is a thermostat and I have it adjusted (per the instructions) to come on when the coolant temp in the inlet tank is at 180° F. There's a probe that goes in between the rad fins.

Running the car at idle takes a few minutes for the fans to kick on and when I turn the car off they run for a couple minutes and stop. A few minutes later they kick on again for another couple minutes. This happens three or four times until the car cools down enough. I think this works better to help the "heat soak" but you could set it up so they only run when the ignition is on.

Driving along the fans cycle on and off depending on traffic. Haven't seen over 190° on the (old) SW gauge. Bear in mind my car is a 4-speed with no A/C.

Hope this helps.

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Phil do your fans go on and off several times after the car has shut down because the on/off temperature is the same (i.e 180)?

I guess that I am a little paranoid about the fans drawing too much when they come on. I might try to get it set up so that one fans works as needed and the other I control manually from inside the car.

My older set-up cycled on/off at the same temperature so it would go on and off half a dozen times after I had shutt the car off.

I would look into a progressive fan controller like the one spal offers, the call it there PWM. It kicks one fan on at half speed when the low temp is reached at the second on at full speed when the high temp is reached. I just installed a Ron Davis with twin fan and these are the best of the best. Just a lil fyi those spal fans pull 30 amps each. Like you I have no ac or power windows,but i do have a 120 amp alt and I have to upgrade now because the fans are beating the snot out of it. I just installed the PWM and my only gripe is that when the temp falls below the low setting the fans wont kick off * scratches head* maybe its just a ground problem. maybe you can adapt an OEM controller to work for you. But on thing is for sure, you want to stagger those fans if you can,cause when mine come one my RPM drops 200 rpm do to the load on the alt. If ya wanna compare notes just hit me up here or drop me a line http://www.nastyz28.com/ubb/smile.gif

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72 RS, ZZ383- 770 Holley, HVH carbspacer and RPM Airgap manifold, flowmaster american thunder system modified with two 40 series mufflers, pro-billet distributer,6AL box, msd super conducter plug wires, powermaster 140 amp alternator and March serpantine conversion.

!!!Piss on C.A.R.B.!!!

I don't know what the amperage is on your fans, but mine each have a 10 Amp fuse and the relay is rated at 30A.

I have the B+ wire from the relay straight to the +post on the battery (Die Hard Truck/Van/SUV battery that was in my GTP before I put the Yellow Top Optima in).

No rpm drop when the fans kick in. The wires don't get warm. They're not staged. Interesting story: The fans were freebies I got 15 years ago where I worked. We had kitted up oil cooler/fan combinations for a Diesel engine project that never got off the ground. They were gonna just throw them away but the boss knew several of were hotrodders and told us:"I'm going out to lunch. I expect you guys to throw all of those kits in the dumpster before I get back. And if you happen to park your cars next to the dumpster with the trunks open and a few of them fall in I don't wanna hear about it." I got four (didn't wanna be greedy). Nice little coolers too.

The reason the fans kick on and off is that when the engine stops so does the waterpump (duh). So the fans cool the radiator to below 180° and kick off. Since the coolant in the block is still over 180°and the 'stat is still open hot water flows up into the radiator due to convection. The cycle repeats until the thermostat closes. It may do it four or five times at shutdown. Yes the on/off is the same. On at 180° and above, off below that.

The only risk in having them run this way is IF the relay ever fails in the closed position (kinda unlikely) the fans will run 'til the battery is drained.

Plus it's fun to watch people near the car jump when the fans kick on...

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[This message has been edited by Phil G (edited July 24, 2005).]