engine and drivetrain Electric fan hookup help

[BVNitta]

I just got a nice 3-row core from Silicon Garage and 3 thermal switches - a 91C, 92-96C and a 99C. (I presume the 92-96C switch closes the circuit at 96C and opens at 92C.) I also have a Hayden electric fan - a few years old, but works fine and about the right size.

a> What do you guys (the ones who made the electric conversion) use as a thermal switch ? I plan to use the car mostly for street but occasionally for autox, here in the northeast.

b> More fundamental: How do you guys hook it all up ? The switch, the fan, relay (and/or fuse ?) and the battery ? Can someone post a simple circuit diagram ?

c> The fan is a pusher - The engine is out of the car so I can't tell if there is room for a puller or not, but I was informed that some 'modifications' are necessary to put in a puller, since there is very little room between the water pump pulley and the radiator. Is this the experience of folks who made this conversion ? Do most of you use pushers ?

Thanks in advance,

Bhima

[Guest Anonymous]

No diagram but it is simple. You really need to run a relay for safety:

1. From the battery to an inline 30 amp fuse to the #30 spade on a relay.

2. From the #87 relay spade to the positive or hot wire to the fan.

3. The fan ground should go directly to a body ground.

4. From some source of switched power (Can usually find an unused one on the bottom of the fuse panel) to the #86 relay spade....NOTE-this will turn off the fan when you turn off the car. Others recommend pulling from a non-switched power source to keep the fan running after shutdown to help cool the car quicker.....but this is not what I would recommend.

5. From the #85 relay spade to one of the spades on the thermal switch in the rad. The other spade on the switch should be connected directly to a body ground. NOTE: You can splice 2 wires together on the #85 relay spade. One wire goes to the thermal switch as above and one wire goes inside the car to a separate toggle or push-button switch and from there to a body ground. This set-up allows you to control the fan if you want the fan to come on earlier (if stuck in traffic) or if the thermal switch would fail.

As far as which temp switch to use...you will have to experiment a little I am afraid. I have my switch in the waterneck which will be hotter than the bottom of the rad. I would guess in that location I would start with the lowest temp and see what you get. Watch the stock gauge and see where it is in relation to the fan coming on and if you set up the fan like I suggest with a cockpit mounted switch, if it starts moving above normal range before it automativally kicks on, you can just flip the switch.

Also, note that you need to set the fan up to be a pusher as in pushing air through the rad to pulling air through the rad from the engine compartment. To ensure this you just need to change the polarity of the wires to the fan...ie red wire could become the ground and the black wire supplies power....

Hope this helps.

[Guest Anonymous]

My last comment about pusher vs puller is a little unclear now that I read it (typed to fast). You want the fan to push air through the rad from the outside air into the engine compartment NOT pulling air from the engine compartment. Clear as mud I hope.....

[Zenon]

I just got a nice 3-row core from Silicon Garage and 3 thermal switches - a 91C, 92-96C and a 99C. (I presume the 92-96C switch closes the circuit at 96C and opens at 92C.) I also have a Hayden electric fan - a few years old, but works fine and about the right size.

a> What do you guys (the ones who made the electric conversion) use as a thermal switch ? I plan to use the car mostly for street but occasionally for autox, here in the northeast.

b> More fundamental: How do you guys hook it all up ? The switch, the fan, relay (and/or fuse ?) and the battery ? Can someone post a simple circuit diagram ?

c> The fan is a pusher - The engine is out of the car so I can't tell if there is room for a puller or not, but I was informed that some 'modifications' are necessary to put in a puller, since there is very little room between the water pump pulley and the radiator. Is this the experience of folks who made this conversion ? Do most of you use pushers ?

Thanks in advance,

Bhima

Use a pusher fan in front of the rad - no room for a puller. The temp of the switch depends on where it is mounted. Prefereably, it would be on the cold side of the rad and turn the fan on when the cooant exiting the rad was getting close to the regulated engine operating temp. Mine is adjustable and I set it to come on at around 70C. IIRC there is an 82C switch used on some BMWs - in your case I'd use that.

If the switch is on the hot side of the rad (or the coolant outlet on the engine), then it has to be higher than the normal operating temp of the engine or else the fan will run all the time. In that case, a 91 or 92-96C switch would be used. To me, this approach has a major downside of letting the engine temp rise above normal before running the fan. But, many manufacturers use this method since they get away with one less sensor by making use of the ECU temp sensor and ECU itself to control the fan.

As for wiring, here is a very rough diagram (created in response to a request arising from another recent thread). Sorry it is not prettier but it should lay it out clearly enough. The relay pins are numbered correctly for any standard automotive relay, however they can vary in layout so look at yours carefully. Beware if your relay already has an internal diode and be sure to wire the relay coil according if so. Also, if your relay is an SPDT type, the 5th terminal will be numbered 87a and is not used in this setup.

regards,

Zenon

[BVNitta]

Thanks. I think I got it. I was given to understand that a pusher is about 20-30% less effective than a puller... not sure why.. is it because it blocks the airflow somewhat or that the air out of a pusher (before it enters the core) is likely to be a few degrees warmer ?

Bhima

[Zenon]

Thanks. I think I got it. I was given to understand that a pusher is about 20-30% less effective than a puller... not sure why.. is it because it blocks the airflow somewhat or that the air out of a pusher (before it enters the core) is likely to be a few degrees warmer ?

Bhima

For practical purposes, that just means you need a slightly more powerful fan than you could get way with behind the rad. So far, based on all the comments I have read about people's '02 electric fan conversions, it seems that as long as you use a fan big enough to cover the rad fairly well, you will have plenty of airflow.

There is also the issue of air "spillage" so use a fan with a built-in shroud and mount it as close to the rad core as possible (but not touching if you can help it!). Here's my 320i one:

regards,

Zenon

[jgerry2002]

As far as I know there is just no room for a puller to be mounted. Both of my cars have pushers.

Though I am wondering if anyone has tried one of those Spal low profile fans (popular with E36 M3 crowd for the fan delete) that have a 2.0" depth. Might be something to look at though considering that the fan probably has more than 2" clearance where the water pump pulley is located.

Take a look at the perma-cool fans. They have a 14" (19114) which I have which pushes a HUGE amount of air.

Hayden and permacool make an adjustable temp sensor which has a an air temp probe. I believe Hayden has a version with a water based sensor.

[BVNitta]

Nice work. You guys are great ! Thanks again,

Bhima

[andrewro]

So, how are you guys mounting the sensor in the radiator? Do you pull the radiator, braze on a fitting, seal things up good and reinstall? I need to do this in the spring and I'm probably going to try it with my '02 radiator unless there is a reason not to do so. If I must I can always grab a 320i radiator from a yard.

-Andrew

[Zenon]

So, how are you guys mounting the sensor in the radiator? Do you pull the radiator, braze on a fitting, seal things up good and reinstall? I need to do this in the spring and I'm probably going to try it with my '02 radiator unless there is a reason not to do so. If I must I can always grab a 320i radiator from a yard.

-Andrew

Late '02 rads and I think all the OE replacements had a 14mm-thread drain plug in one end of the lower tank instead of the original 6 or 8mm plug on the rear face of the lower tank. The 14mm thread is the same as used for the 320i and most later BMW rad-mounted temp switches. (BTW, It also matches the stock '02 temp gauge sender.)

If you have an early-style '02 rad, I suppose you could have a rad shop install a bung. If you go that route, maybe install a bung to suit whatever temp switches (in the desired temp range!) are most easily available to you, be they german, japanese or 'mercan.

So that the engine thermostat always has a supply of colder coolant so it can do it's regulating job, I recommend a ~70C on point for a switch mounted in the lower tank, but I know at least one other guy here will dispute that. FWIW, my fan only ever comes on at sub-10mph road speeds and not much at that, and the engine temp never runs more than one needle-width above horizontal on the gauge - I consider that to be ideal with an 80C t-stat.

regards,

Zenon

[Zenon]

This awesome diagram was created by Shaun Feruglio (an '02 brother from down under) based on my ugly drawing from above:

Any electrical errors are my fault - if you spot one please point it out. Note that the diagram looks to have a real diode and a symbolic one in series - you only need the one real one. ;-) You can also use any other equivalent or better rectifier diode. Just make sure it can handle at least 50V PIV and 1/2A current.

Thanks to A. Carlson for the drawing that, though it had a booboo, had it's heart in the right place and was the inspiration and catalyst for the creation of this one.

regards,

Zenon