Fan power

[Ponymedic]

Not sure if this is an issue or not
my fan often stays on 5 min or more after the engine is shut down. This is after normal driving in 50degree weather. I assume it shuts off when the radiator cools but I dont love the look. Is this normal? What have others done ie. Wire to another circuit?

[i.e.427]

If you have an aftermarket EFI like Sniper or FiTech the computer shuts it off when the ignition is turn off. If you have a carb I generally wire the trigger side of the fan relay to a switched circuit in the harness so it shuts off when the ignition is turned off. There are spare circuits in the harness you probably aren't using that you can use to trigger the relay.

[FLPBFoot]

As i.e. said you can go to a switched circuit or go a switch route as I have. I have a 427 carb motor and the fan relay with the RF harness is wired to the temp sensor on the motor by the thermostat housing. This will cause the fan to run for a long time after the motor is shut down while the coolant at the top of the motor cools. With no circulation in the system the fan is doing little to cool the top of the motor. I have put a DPST switch in the relay circuit and have it wired for "Automatic", "Off", and "On" giving me complete control over the fan operation. Nothing worse than pulling into a car show and your fan sits there and screams for 5 to 10 minutes. I just hit the Off position and all's good. As these cars have a relatively small battery I'm also concerned about conserving power so when it comes time to spin that high compression large engine there is no issue. Once I start the car and back on the road toggle to Automatic and let the temp sensor in the block control the fan.

When it is VERY hot out I do let the fan run so to cool as much fluid in the radiator as possible to help control overall temp once back on the road. Good news is you have choices for solutions.

Steve

[Mike DiGiorgio]

This is a great time for a time delay relay (like this) https://www.delcity.net/store/Time-Delay-Relays/p_804415.h_804416.r_IF1003?&mkwid=s&crid=456573819067&mp_kw=&mp_mt=b&gclid=Cj0KCQjw4ImEBhDFARIsAGOTMj_Iura0e68KSlSgrSzj 3dkOmrzK0w_sKay7VFdyK4wzwgk-PexZ4mAaArmsEALw_wcB

the ground side of the relay is based triggered via temp sender, + trigger side from ignition key. set relay to 1-3 minutes after key shut off so fan will cool rad down, but not forever after key off.

[edwardb]

Just to be 100% clear -- although the posts above refer to it -- the current version of the Ron Francis has the cooling fan power/relay on the battery power circuit. Meaning it's always got power as long as the battery is connected. That, along with whatever the sensor setup you have, will allow the fan to run even after the ignition key is in the off position. So any override you do just needs to break the power or ground to the cooling fan relay. Either with a relay wired to the ignition side or a manual override switch. Both as suggested.

[skidd]

Ok.. what you describe is not normal.. but.. I can imagine it happening... and why.
The power to the fan on a typical wiring harness actually does come directly from the battery. (I'll explain why in a moment).
The trigger that engages the relay that provides that power is almost always a "ground" trigger. Meaning that something "grounds" the relay to start the fan. Your in-block temperature sensor.
Then, the power to the relay coil... that power needs to be on a switched circuit. Based on the ignition key.
The important thing here is that the 2 - 12v power sources to your relay, must NOT be on the same circuit. (see below)
If they are both on constant/battery, then your fan will stay running as long as the temperature is above the sensor trigger.
If they are both on switched 12v, then your fan will power your switched circuit, and actually keep your motor running (see below)

This is roughly what you want.
Battery 12v --> POWER INLET side of relay that feeds to the fan.
Switched 12v --> Trigger / Coil side of relay
Ground of Trigger/Coil side of relay --> Temperature Sensor

In the case of your wiring.. I would look at that trigger/coil 12v side of your relay. It should be connected to a key switched 12v source. Not a constant 12v source. My Money is on that it's wired to a constant source somehow.

Now.. why should the fan power side of the relay be connected to a constant 12v battery source?
Because the inertial momentum of your electric fan, will actually feed back 12v to the circuit it's connected to.
Ask me how I know? lol. The 12v hotrod wiring harness I bought, has the 12v power and trigger to the relay .. all connected to the same switched 12v circuit.
The problem with this setup is that when the inertia of the fan keep spinning.. it back-feeds 12v to the switched circuit. This back-feed actually keeps the fan relay engaged (both 12v terminals on the relay are connected).
Having the fan keep putting 12v back into the switched circuit.. also kept power going to the Coil!
See where this is going?
yes.. as long as my fan was spinning under its own inertia.. the engine kept running. The motor would stay running for about 2 seconds after turning off the key. It didn't stop until the back-fed 12v fell below enough current to keep the fan relay engaged.
This is why the fan relay needs to have switched 12v feeding it's trigger/coil.. and the power to the fan on the constant battery 12v circuit.
If you kill power to the car (turn off the key) , it stops 12v going to the relay trigger side. And since the fan inertia is feeding 12v back to the constant side, it can't keep the relay powered. So, the relay opens, and the fan spins down, and your car shuts off!!!!

On my wiring harness.. I traced the wires and confirmed that power 12v pins on the fan relay were both wired to switched 12v.
Basically... a mfg mistake. I had to disconnect the 12v pin that powers the fan, and tie it to constant 12v. After that, everything worked perfectly.

Sorry.. I know that above explanation is confusing and hard to follow... its' kinda hard to explain.
I hope that makes some sense.

[Papa]

All great advice and explanations above. but because I'm a visual guy, here is my version of how a fan relay circuit works:

https://thefactoryfiveforum.com/attachment.php?attachmentid=146828&d=1619192489

1. For any electric component, like a fan, to function it needs a complete circuit (power and ground).
2. A relay is a way to allow high current drawing items, like a fan, to be switched on and off without putting that high current through the actual switch.
3. In most fan circuits, the switch is actually on the ground side of the circuit. This can be a mechanical thermally activated switch, an EFI computer-controlled switch, or a manual "override" switch.
4. The relay is set up to connect power from a battery source to the device (fan) by connecting pin 30 (relay power) to pin 87 (device power) when pin 86 (trigger) is powered AND pin 85 (ground) is present
5. In most fan circuits, pins 30 and 86 are always powered and the circuit for the fan is completed when the ground is connected
6. In your case, pin 86 is an always hot battery connection, so anytime the ground is complete, the fan is powered on.
7. To change this, make pin 86 a keyed power connection. By doing this, the fan can only run when the key is on because the switch inside the relay is closed only when power is supplied to pin 86 and the ground is completed.

Make sense?

[Ponymedic]

Im a visual guy as well this is great thanks

[AC Bill]

Since it's completion, my roadster has done that. Many manufactured cars do as well.

After the engine is shut off, temps under the hood often rise significantly. The fan blowing air, besides lowering coolant temps, also removes excessive heat from the engine, headers, and other engine compartment components, which are no longer being cooled, as when your moving. This air movement, can also help keep the foot boxes, and firewall cooler. On a hot day, it could keep the interior a little more comfortable, especially if your only parked for 10 minutes, before jumping back in.

I have a manual over-ride fan switch, so sometimes as I am approaching home, or wherever I may be shutting the car off, I will turn the fan on a few blocks before arriving. This cools the car down enough, so when I do park, and shut it off, the fan only runs for a minute or so, if at all. I'm not big on car shows, other than a spectator. The odd time I have entered one, fan run-on never concerned me. Most people are familiar with it these days.

[CraigS]

Papa's diagram is fantastic. For reference for anyone else looking at fan wiring I added a dash switch.
https://live.staticflickr.com/65535/51135071556_71205ea60f_z.jpg (https://flic.kr/p/2kUCBfL)Fan relay (https://flic.kr/p/2kUCBfL) by craig stuard (https://www.flickr.com/photos/152454123@N04/), on Flickr

[Blitzboy54]

I’ve been a member of a lot of forums. I’ve never seen anything this like the level of support and community.


You guys make this so much fun.

[Ponymedic]

UPDATE followed papa's advice (not the first time) worked great.As blitzboy said the level of support is great