Wiring for External Oil Cooler fan

Hello all,
I am getting ready to install my external oil cooler in my VS and I have everything pretty much figured out except the wiring. I am an inline thermostatic control with the wires on it and the wires coming out of the fan.

I know that the black wire from the fan is the ground and the blue goes to the switch. The other wire on the switch should go to a power supply. From there I was thinking about running it to the coil. Would that be a good idea? I was thinking that I should put it on a fuse but not sure how I would do that.

Well, thanks for reading and your help.

Cooler fan motors have a heavy draw on intital start up.
Run a #12-14 gauge wire up to the dash switch, the other side of the switch goes to a good ground source i.e chassis ground completing the circuit.
Power wire connects to at least a 25 amp in line fuse(see manufactures rating) the other side of the fuse to the positive (battery cable) connection on the starter solenoid. Avoid the coil as a power source due to the heavy initional draw.

You have 2 methods to accomplish this task... One is to have the fan wired hot so even if the engine is turned off, your fan will cool the oil in the cooler or, the better way is to have the fan motor driven by the ignition. In other words, if the ignition is on, then the fan motor can start based on oil temp. If the ignition is off, the motor will not start.

On customer cars, I prefer to use a relay as it takes the load off of the internal switch and places it within the relay. Don't forget to install a by pass switch.

Thanks for all your help. I am going to buy a nice toggle switch to mount on the dash board.

Hidden switch under the dash "looks" better.

perhaps my advice is ill advised, but.... I am going to add a cooler as well and I am going to use the coil BUT I am going to run it off an on/off switch. I know that there is a lot of draw, but I do not plan on running my blower from the start. I would use a toggle switch on the dash to switch it on if I am sitting in traffic, or if I am running it raw. Perhaps it is just me, but shouldn't the option to run a cooler be made if you don't run a thermo?

If you're interested, I can scan the wiring diagram I made to wire up my cooling fans and post it. I use the thermostatic switch AND a manual over-ride switch with an indicator light (to tell me when the manual switch is "on") in case the thermo switch fails. I also use a small inexpensive relay to supply switched +12VDC power to the circuit from the fuse panel. However, I also added a second fuse panel because of the other stuff I've added,i.e. interior lights, "trunk" lights, engine compartment lights, fog lights, emergency fuel pump switch, etc. etc. That's what happens when you spend your life in the aerospace industry. In fact, I got fed up trying to fight my way through the VW electrical schematics and finally made up my own signal light circuits and emergency flasher circuit and panels. I'm reasonably sure that both of the little relay and flasher panels I made up cost less than the VW headlight and emergency flasher switches...and you can get all the parts rather inexpensively at your local auto parts store. Since no oil is moving through your external cooler when the engine is not running, I see no reason to run the fans AFTER you've shut the engine down.

I was thinking of putting it under the dash because I didn't really want to drill in the dash at the moment.

Hey John I would love to get a look at that. Thanks.

I'm using two 16-pass Derale coolers. They draw 6.5 amps total when both are running. On startup, they draw about 12 amps for 1-2 seconds until the get up to moving. As you can see, I destoyed any semblance of originality in the cockpit with my switch panel. On the positive side, I don't have to try and remember where I hid a switch when it comes time to activate the function it controls. I've certainly dated myself with the use of the mechanical relays... a hold-over from my days with Atlas missiles in San Diego.

I should have mentioned that the "E-OIL" switch is used to bypass thermostatic fan switch in the event it fails. I've included the circuits I used for my fuel pump and the emergency flasher/turn signal lights as well. You may not be able to read them since I had to use photos in jpeg format. If you should need a better view, I can email a scan in .pdf format which is much clearer, but the file is 10 times larger. The fuel pump circuit allows the engine to start with zero oil pressure and no cooling air, but then shut the engine down if you experience low oil pressure or loss of engine cooling air. Again, I use mechanical relays...which works for me. I also realize that there are situations where oil pressure can go low after running hard, or worse, on a hot day in slow traffic. However; all you have to do is increase you engine rpm if you have a false "low oil pressure shutdown", or actuate the E-FUEL switch if you're SURE you have oil pressure (and not an oil pump failure). These sketches were only for my car and may be riddled with errors, but they work for me and may give someone an idea for a better way...or at least something to stay away from if they so choose. By the way, I did include one hidden switch to disable the fuel pump...if I could only remember where I put it.

Thanks John. They are clear enough. I was able to print them with enough quality to read them. I am going to take them to a guy I know so he can help me.

I still want it to shut off when I turn the car off though.

You live in Grand Terrace (215 bet. 10 and 60?)

If you need a mechanic, I do a lot of work for the Spyder crowd and several Speedster folks.

I'm in Ontario

I thought about the postings I made here and remembered today there was an error on the fuel pump circuit sketch, so I'm posting the correction now and deleting yesterday's sketch. The error was that contacts 2 and 3 were reversed on the "main Fuel" relay. I corrected the wiring long ago, but didn't update the sketch. They are correct as shown below. Contact 3 is normally open and contact 2 is "normally closed" and the sketch depicts the relay after you have just turned the ignition key on. Sorry 'bout that.

By the way, I'm not sure I understand your concern on the fan shut down coincident with engine shutdown. Since I used a "switched" 12VDC source for the cooling fan circuit, they will shut down the moment you turn your ignition key off.

Hey John,
Thanks for tip. I didn't understand some of the symbols and things on the your sketch which was why I took it to my friend. He said it was nice btw. I am going to study it and figure out how to apply it to my car.

Also, I may have to take you up on that Larry. Don't be surprised if a Speedster gets towed down your way.

John, just a quick note on your oil cooler fan citcuit. The oil temperature switch ought to be relocated to immediately before the relay coil. That way, the relay contacts (rather than the switch) take the heavy current and inherent arcing.

I won't be the first time a Speedster or Spyder has been towed to my home. Let me know of your intentions LJOWDY at AOL.COM

Brian, thanks...that's a positive improvement. I figured the factory design incorporated a switch that was as robust as the relay (30 amp), but you're right, it would certainly be easier to replace the relay than try to find another switch should the current eat up the contacts. Right now, I'm going to resist standing on my head trying to get to the circuitry, but it's certainly on the to-do list when I'm back under there. I've posted a revision to incorporate Brian's suggestion.

Thanks again for the drawling. I have been studying and how to apply it. I start the wrenching tomorrow.

@Larry...Thanks so much for you support. I will drop you email if I run into some snags. Lets hope it all goes well.

Hi, been reading this thread and am about to mount an external cooler. Questions: should it be mounted in the wheel well, probably left. And is it absolutely necessary to have a cooling fan. Won't the air flow at speed cool the fins?

Thanks and I'm sure I'll have more questions

Jay

I mount oil coolers flat above and forward of the drivers side axle, there is just enough room to stuff it there. Since it is horizontal, yes a fan. Never trust slip on hoses and hose clamps. You can have custom hoses made up with the correct threaded ends done for about $75 at a hyd. hose place.