I wish to wire the fans to stay on when key is off, and engine is hot. Tonight, after tuning a bit on the start up coefficients, I idled the car for long enough to get the heat up to 210 degrees, then turned the MSD box off, (it has a seperate kill switch) thus killing the engine, but left the switched 12V on, which left the fans running. They stayed on for 3 minutes with the outside temperature at 80 degrees, and then the fan tube thermostat turned them off as the radiator temp came down.

Does anyone see a problem with wiring the fan relays to the unswitched 12V? Is there some hidden problem I don;t see? Such as maybe the fans might potentially stay on indefinitely and run the battery down. I know some OEM setups will keep the fans on after the key is off, but don;t know if this is timed, or just shuts off with the termostats. I can imagine a timing circuit that would stay on longer than the predicted timing of the fan thermostats as a back up failsafe, but have no knowledge of how this circuit would actually be designed.

The goal is to try and limit the heat soak in the engine. If I drive the car to the bank, and leave the engine shut off for 5 minutes, when I come back and restart it, the AF ratio is very lean for a minute or so because the intake manifold has gotten quite hot while sitting. One of the few nice features of the Accel computer ECU was that there was a trim screen for enrichment when the manifold got too hot this way. Once tuned, the heat soak did not effect starting AF ratio.

Once the fans cut off, I restarted the engine, and it idled at 15.5 for a minute or so, which was not ideal, but better than when it was left to heat soak with the fans off. At least it did not feel like it was going to die.

Any thoughts about this? Anybody know what the strategy is in the electrical circuits that keep the fans running after engine shut down. My Old VW RAbbit had this feature, along with a sign on the radiator that said, "Keep Hands and fingers away. Fan can start with Engine not running". Any thoughts are appreciated.

Sam

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Hi Sam. I have a VW Passat with the same feature as your Rabbit, the fan comes on when engine stops, and runs until a preset lower temperature is reached. The run-time for the fan varies a lot, the temperature switch obviously shuts the fan off. The car is an '82 model, and has never given trouble with running too long.
As I see it, there are two easy ways to control that the fan doesn't start without your knowledge.
One is to put a timed cut-off switch in the circuit.
The other is simply wire in a double relay that bypass the normal power feed from the ignition switch 'Run' circuit and lets the fan run off the battery as long as needed when given a signal from the thermostatic switch. When the signal disappears because the lower temp is reached, the relay cuts the bypass power feed so the fan cannot restart without simultaneous input from the normal feed again, thereby preventing any random start of the fan at a later stage. This is the system I will make for my installation of electric fan. I am pressed for time right now, otherwise I could have made a schematic, but it should not be difficult to make. There are lots of different relay layouts to choose from.

I also have the circuit diagrams for the VW somewhere, I'll see how they approached the matter, and come back with an update.

Olaf.

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Aspenized

Thanks Olafla. I understand the double relay circuit. I appreciate the offer on the VW manual. Take you time. This project can be started with the double relay circuit and upgraded with further info.

My Rabbit was a 75. I bet your Passat was a spin off from the Rabbit design.
I owned the Rabbit when I had my first A body Mopar, which as a '72 Duster. Both cars carry good memories. The problem with the Rabbit was that I beat on it the same way I beat on the Duster, and it just did not have the strength of the Duster. I was always going through brakes and clutches on the Rabbit. I have calmed down in 32 years and pretty much baby my cars now.

Sam

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I see no problem wiring the fan thermostat to control the on/off function. It is very unlikely to kill the battery unless you run something crazy like a 100 degree thermostat, or temperatures in your town approach 180 degrees (or whatever temp turns on your fan). Then you'd have bigger problems!

I ran my Ford this way for a long time. Fan stays on until it drops below the temp the thermostat senses, then there is no further drain on the system.

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If it was easy, everybody would be doing it.

Thanks for the feedback. Olafla, I thought I could logic out the double relay concept, but I could not. I would appreciate it if you can supply a diagram when you get time. In the mean time, I can just move the feed from switched to unswitched +12. They are just a few inches apart on the inner fender.

Sam

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I have a temp sensor in the cooling fins of the rad for the fan relay. It has been this way for 3 years now. I have a mechanical dial in which I can set the temp for the fans. They cycle on and off as the heat soaked coolant naturally convects (?) out of the engine and into the rad. Mine is old fashioned and works. I've never had a battery issue either.

I also have a manual override in the car to turn on the fans sooner if needed.

I see no problem with you doing it.

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11.02 @ 120.56
http://www.youtube.com/watch?v=EAxRmoDgsdY
Chassis dyno
http://www.youtube.com/watch?v=wd6hFGzLJMc

I run a temp sensor screwed into the top radiator tank that cycles the cooling fans on and off. I leave my system switched on all the time so it can cycle on and off as many times as it needs to on hot days when heat soak would be a problem.

I have never had a problem with battery power or restarts. In fact, restarts are almost immediate since the carb has a heat deflector under it which acts like a cooling heat sink with the fan blowing on it, the carb body stays cool. No heat soak problems at all!

Click on the red link below for pictures.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

You also need 2 diodes with the 2 relay system.

The second relay can be small, as it only needs to power the first relay.


Can't draw a picture, but here goes:

1st relay (power)

Power input goes to battery
Power output goes to fan
Coil output goes to thermosensor (assuming sensor grounds when hot)
Coil input goes to power output of 2nd relay.


2nd relay (control)

Power input goes to battery
Power output goes to coil input of 1st relay
Coil output goes to ground
Coil input goes to an ignition source (through a diode).


As described above, relays will only work with ignition on.


Now add a wire (with a diode) from the power out of the 1st relay to the coil input of the 2nd relay. You should end up with 2 inputs to the coil input, with each wire having a diode.


The fan will stay on until the thermosensor turns off, then stay off.

If you shut down and the fan isn't running, it will never start up.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

That's exellent, emsvitil! For those unfamiliar with electric components, a diode can lead current in one direction only.

I know there is a relay type that use two inputs to activate, but need only one to hold active, the downside with those are that a delayed start from heat soak will not register if the ignition is already turned off. Emsvitil's solution is simple and easy to fabricate with cheap standard parts.
Olaf

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Aspenized

I'm a little confused about the problem.

When doing the electric fan conversion a few weeks ago, I thought about leaving the fan relay powered when the ignition is off. Decided against it because there's no coolant flowing when the motor isn't running. There didn't seem to be much advantage to letting the fan run by itself, other than cooling the engine a little faster when the car doesn't sit long before being driven again.

It could be that I just don't understand heat soak very well. I've never heard the fan on my '06 Civic continue running after shutting it down, so I didn't think it was a problem.

Could someone fill me in on how serious heat soak is? I'm always happy to learn, and it wouldn't be difficult to rewire my fan to keep running after I shut the engine off.

Ems, Thanks. What kind of diode should I look for when I go into Radio Shack? Are there power or voltage ratings that I need to be aware of? For starters I think I will just hook the coils right to batt voltage. Yes the thermostat serves to complete the ground on the relay coil. The relays turn on the fans. I have two relays because there are two fans, and plans to set them at different temperatures if I purchase a second thermostat.

Just for the record, I did have one of these thermostats fail one time in way that they would not turn on the fans. It seems conceivable that they might fail in a way that they did not turn off the fans. In tha tcase, a back up timer might be helpfull. Of course that circuit could fail as well I suppose.

Sam

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http://www.radioshack.com/product/index ... Id=2062589


You'll eventually use them, much better deal than 2 for $0.99

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Sam,

We had a new 1981 Plymouth Reliant wagon equipped with 2.6L engine, and air conditioning that would run the radiator fan after ignition shutdown. Drove me nuts, people constantly telling me the car is still running after parking it… Same with those delay headlights when they became common on cheep cars. Hey… your lights are on.

My 82 Lebaron with the same engine & air conditioning dose not continue to run after shut down. This was a one year feature. Perhaps the wiring diagram for the 81 is available, and would present an easy adaptation to your Dart.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Sam,

Go to Engine FAQ and look up my simplified wiring schematic
Electrical FAQ-More Ignition information for the fans.
Been running it for 6 years now and no problems!
I can turn the fans on at any time or let the thermostat switch do it and I can leave the system active or turn it off after engine shut off. It is extremely simple.....only one relay and no diodes to pop.....!
Don't make it any harder than you have to......

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Thanks Ted. That looks like a good circuit. I enjoyed your web page. It was nice to see you and your cars. It appears you have more than one old Mopar, unless those photos are of other's cars.

If you wire to batt for your +12, then the fan still has the option of coming back on once cooled off, and the heat builds back up. I did not see a way your circuit prevents this. This will happen on mine now that I have hooked the circuit up to the batt instead of keyed +12. Am I misreading yur circuit?

My wife came back in the house last evening to tell me that when she passed the garage it sounded like the car had started up. Of course this is not necessarily a bad thing. It does serve to eliminate some heat from under the hood. I have felt the back edge of the hood, and the fender vents I added, and there is indeed warm air flowing out those vents when the fan is running.
Sam

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