[al bundy]

I'm in the process of installing an electric fan for cooling purposes in my 40 chevy coupe (has a 1981 Camera v8 350). Do you recommend the fan be hooked up so that it only runs when the ignition is on or should I wire it direct so that it runs until it has cooled the engine down ? Thanks in advance.

[advanced design]

I would wire it to turn on / turn off based on engine temperature and when the A/C is turned on.

[docvette]

Doc here,

I like the best of both worlds....

Hook it up to run thermostatically controlled, with a manual override switch on or under the dash.

Those controllers have been known to fail at the most inopportune times..and an override will insure you get home.

as you probably know, Don't forget to install a relay...fan motors are a high draw item, and can burn up a harness or a simple switch contact.

Doc

[al bundy]

Originally Posted by advanced design

I would wire it to turn on / turn off based on engine temperature and when the A/C is turned on.

Excellent suggestion. Any idea how much drain or impact on the battery if the fan continued to run after the engine was turned off ?

[docvette]

Doc here,

Impact on the battery would be minimal if the fan were to run for 5 minutes or less after shut down on a properly operating charging system and battery...

Certainly no more than leaving the headlights on while unloading the car and opening the garage door at night with the engine off...

Most new vehicles have the fan run after shutdown for a few minutes to bring the heat soak temps down, with no effect on the battery.

Doc

[outlaw17]

I have read that it is important to have 2 relays to prevent a slow meltdown of the harness , can someone explain how to put in 2 relays . I am installing an elecric fan in an old car with a 350 TBI and all the wiring from a 93 truck.

[docvette]

Doc here,

One relay for the fan motor is totally sufficient provided you have the proper size relay for the task at hand...

If your going to thermal control the relay, your control circuit will consist of the coil wire from the relay via a properly sized fuse and then to switched power..The other side of the relay coil will go through the sender, and ground via the sender at temp..you can run 18 gauge wire for this.

The contacts will wire thusly, with the PROPER gauge wire for the current draw of the fan motor, run a wire from either switched power or battery, through a PROPER size fuse or link for the motor circuit to the normally open contact of the relay, the center wiper of the relay will go to the fan motor power...via a properly size wire for the draw..

When the sender reaches temp, it will close the coil circuit energize the contact and power up the fan..as the temp drops, the coil goes open to ground, de~energizes the contacts and the motor stops..

Options can include a manual override switch (on all the time, bypassing the sender) or a time delay on shut down power continues for a period of time after engine stop to aid in heat soak..(you'll need a TDR time delay relay for this option, or a combination of Capacitors and resistors to equal time in delay)

I see absolutely no reason to run two relays for this function UNLESS you have two fan motors in the same shroud...and even then YOU could get a double pole single throw relay with contacts rated at or above the motor draw (might be more expensive than 2 spst's though)

Doc

[outlaw17]

Thanks Doc , I'll go with just one relay . Now can anyone tell me what kind of sensor I need to get to operate the fan ? Can I just go get one off a car in the jusnkyard ? If so ,which one ,on what type of car and engine ?

[horvath]

Hey, Al

I have a Chevy sb 350 with headers and a mild hydraulic cam in my pickup ... I'm using a thermo-switch that turns my fan on at 190*, off at 170* (I think those are the temps) ... the idea is to keep my 350 operating at around 180*.

Also, I ran 2 relays on my electric fan because of Mad Electrical -- and although I respect Doc BIGtime, I really dig Mark Hamilton's reasoning -- See Here (scroll down)

Here's how and why I did double relays on my 16" electric fan:
Click Here

And if you want to understand relays and how they work; the different applications you can use them for ... here's my low-down:
Click Here

Alan
54 Chevy Pickup

[outlaw17]

Those are awesome examples , great information , but I still need to know what sensor to use , and also where is the best spot to put it ? In the head or up on the intake ?

[horvath]

The intake, near the rad hose, is where mine is and that's the most accurate spot for temp readings.

As far as what kind to put in, you just go by the temps ... if you have a 350sbc engine, get a 170/190 thermo-switch.

PS - I strongly suggest using a fusible link instead of a circuit breaker. Originally, I had a single relay and a circuit breaker on my 16" fan and when it kicked in, my voltage gauge would hit the basement! After installing the double relays and a fusible link, I hardly see the voltage gauge react at all!

[Rob (chuck) Berry]

G'day from down under. One of the questions you asked originally referred to whether you should wire your fans battery direct or through the ignition. Personally I can't see a reason for having a cooling fan running after the engine is shut off, as mehanical fans and electric fans in factory systems shut off with the ignition. With the standard 30 amp relay, I would tend to feed the 85 terminal on the relay from the ignition switch and earth to 86 terminal through the cooling fan temperature operated switch (most are normally open switches which close at about 170) terminal 30 has the input power (with a 50amp fusible link) and 87 goes to the fan motor. the fan should be earthed well and so should the radiator. Make sure you use a spike protected relay with a diode in if you have electronic components in your system.

Ooroo