Two fans, one truck

[n33k0]

Hi everybody,

My 1972 C10 has two fans mounted on the radiator, but only one of them works. The fan on the driver side of the radiator is hard-wired to a toggle switch in the cab and that controls when the fan is on or off (I always leave it on). It is mounted on the outside of the radiator (against the side of the radiator facing the grille), and it pulls air out of the engine bay. It seems to work just fine, the issue is with the other fan.

The other fan is mounted on the engine side of the radiator, and seems to pull air into the engine bay through the A/C condenser and radiator. It has a wiring harness that plugs into the back of the fan housing, with two wires coming out of it. One wire seems to run to the positive terminal on the battery, the other runs into the cab where the previous owner connected it to the B/U LPS fuse. This doesn't seem like the correct way to power the fan, can anybody enlighten me how to get the fan wired properly?

I noticed the temp gauge rising steadily while sitting in traffic, creeping close to 220*, that is when I looked under the hood and noticed the fan was not working. I replaced the 10amp B/U LPS fuse and it kept the fan running for about one minute, then the fuse blew and melted. I'm hoping the faulty fan is the cause of the temperature problem, and it obviously is not working properly wired the way it is currently.

Thanks for the help,
-Nick

[davepl]

Use a relay. The power for the fan(s) should come directly from the battery or distribution block next to it. The signal to turn the fans on is whatever you choose it to be (a switch or a themal sensor or whatever) and then merely turns on the relay so that current flows to the fans. I guess there's nothing technically wrong with using the backup light circuit as a trigger power source, but I'd stick with IGN or ACC.

That prevents running any (significant) current through the switches and so on.

Modern vehicles are nowadays built with what amounts to one power wire, one CAN BUS wire, and a crapload of relays. I think my truck has at least 50.

I just added a big 3000cfm pusher to help one of my cars in traffic, and wired the relay trigger to a "210 on, 180 off" switch in the head. You have to match that up with your thermostat so that it turns on above the thermostat setting and off below it.

Edit: Summit carries all kinds of stuff like this, have a browse over there.

[n33k0]

Thanks for the quick reply and advice, Davepl. So a fan relay is what I'm looking for, like this?

http://www.summitracing.com/parts/der-16764/overview/

I'm learning about electrical systems as I go crossing them off my repair list

[piecesparts]

You have two fans and they are mounted on the radiator Opposing each other. I am going out on a limb here, but that is just insanely odd. First of all why are they pulling from different directions? Also, fans that are mounted on the front of radiators, routinely are less efficient than ones mounted behind the radiator. However, yours pulls from the engine bay and that is not a norm, in my world. Second, have you ever had overheating issues with this setup, especially in Florida?

[n33k0]

I've only had the truck for a month, and only noticed the temperature issue a week ago. The way the fans are set up is a bit strange, they are staggered so that together they move air across the whole surface of the radiator.



That's the way the previous owner had it set up, and the temp never climbed too far above 190* for the first few weeks I was driving it. The one in the bottom right corner of the picture is always on, pulling air out from the engine bay. The other fan on the left side of the picture is the one that doesn't work properly... the fan is not broken, but the way it is wired is causing it to blow the fuse and lose power.

[piecesparts]

Apparently someone has an idea that should work. My experience is that you are circulating your hot air and NOT accomplishing much for cooling. If you contact any of the larger fan companies, such as Be cool, Flex-a-Lite, or Zirgo, they will tell you push/pull is not an effective design. Just my $.02 worth. I am running electric fans on my 383 stroker engine and my design is that one fan comes on when the temp gets to 180 degrees and the other fan comes on if the temp increases to 200 degrees. I have manual switches, but only use them if there is a relay failure. Do some research and then go forward with a change. Pusher fans are rated at a lower effectiveness than a puller fan, due to the fact air is lost before it goes through the radiator. The higher the airflow, the more effective the fan. Many fan manufacturers will give a rating in SCFM, but you should ask them if that is flow measured against a resistance or is it measured into a open air space. Be Cool taught me a lot when I sat down with them on a Hot Rod Power Tour a few years ago.

I attached two pics, one from my 84 with the stroker engine and one from my old 91 daily driver.

[n33k0]

I just wanted to say thanks, fellas, the addition of a relay worked and the second fan is running as it should now. The truck doesn't go over 180* sitting in traffic, but it still got close to 200* after coming to a stop after a cruise on the highway... I'll chalk that up to regular operating temps considering the workout the engine gets at higher speeds with a 3-speed and 4.10 gears.

Now that I can enjoy the truck again, i can start thinking about what to do with the fan in front of the radiator I'm not convinced it's contributing much to cooling the radiator, time to run some tests with it off and see if I can eliminate it.

Thanks again!