Why do I keep killing aux fan switches?

[CorvallisBMW]

I'm running an e36 aux fan switch on my m30 swap, p/n 61-31-8-361-787. I have it hooked up to the stock wiring, relays, etc. but instead of activating the stock aux fan it runs a Spal 400mm pusher.

I also have an override switch on my center console that lets me turn it on manually. The switch simply connects in-line with the temp switch wiring, essentially letting me close either the high or low speed circuit on demand (all of which is on the signal wires coming out of the switch, not the power wires post relay). I also have each of the circuits hooked up to 12V LEDs on the dash that tells me when either high or low is active so I can monitor the system for proper function.

My problem is that my car seems to consume them at a rate only slightly slower than that which it consumes fuel. I have to replace it every 2-3 months as it will slowly begin to activate less and less often. The temp will begin to rise but the fan won't kick on. I'll turn it on by hand and wait for the temps to drop before turning it off again. Next time it starts to get hot again, the fan suddenly works again. Then the next time, not. Then it does, then it doesn't, etc... As the switch stays in the car longer, it gets less and less reliable. I'm at a loss as to why. I'm on my 4th switch in less than 10K miles on this swap

Any electrical gurus out there with some advice?

[jlevie]

Unless there is a fault in the relays that is causing excessive current flow through the thermo switch there is no reason for the thermo switch to prematurely fail.

But your description of the failure progression makes me wonder if there might not be a very small head gasket leak that is pumping air into the cooling system. If the top of the radiator fills with air the thermo switch will appear to have failed. Have you tested any of the "failed" switches to see if they are really bad?

[CorvallisBMW]

I have not manually tested them but I will the next time I pull a "bad" one. I've never found any signs of a HG leak but you never know.

[CorvallisBMW]

Maybe I'll swing by a radiator shop and have them test my coolant for hydrocarbons...

I did crack the bleed screw the other day and there was some air in the system but not much.

[CorvallisBMW]

So... thread bump!

I finally got around to having a shop check the coolant for hydrocarbons. None present. No signs of a HG leak.

I'm starting to wonder if I need a better way to bleed the systems, AKA pressure bleeding or something like that. I also need to check all the wiring I guess, see what's going on there. I still keep finding air in the system though...

[Chuck C]

You buying factory or aftermarket? I had 2 switches from WorldPac fail closed, so the fan was running all the time.

[reelizmpro]

You have to submerge it in boiling water and test it out with a meter. I had a similar problem that ended up being bad connector contacts. I ended up buying new terminals and connector. Apparently, this is not uncommon.

[jlevie]

So... thread bump!

I finally got around to having a shop check the coolant for hydrocarbons. None present. No signs of a HG leak.

I'm starting to wonder if I need a better way to bleed the systems, AKA pressure bleeding or something like that. I also need to check all the wiring I guess, see what's going on there. I still keep finding air in the system though...

Using a vacuum fill system eliminates any need to bleed the system and is the best way. But using the correct bleed procedure (see below) works almost as well.

1) Using ramps or a jack get the front of the car 1' or more higher than
the rear. That will make the radiator and bleed screw the highest point
on the engine and facilitate removal of air.

2) With the bleed screw open, add coolant until no more air comes out of
the bleed.

3) Leave the filler cap off, or at least loose, and set the heat for max
temp and fan speed. Leaving the cap loose will prevent air that's still
in the system from causing a "coolant fountain" once the engine heats
up. Start the engine and allow it to warm up to operating temp. As it
warms up occasionally crack the bleed screw to release any air and top
up the coolant as necessary.

4) Once the engine is at temp bring it up to 2000-2500rpm for a few seconds
several times. Then crack the bleed until no more air is released. At
this point the heater should be throwing lots of hot air, which
indicates that the heater core is filled with coolant. You may have to
repeat this a few times to get all the air out.

5) Drive the car a bit, allow it to cool back down, and recheck the
bleed for air. Over the next few days you may get very small amounts (a
few bubbles) of air out of the bleed screw.

After fully bleeding the system, drive the car for a few days and re-bleed. Release of a significant amount of air then or later is evidence of ahead gasket leak. And if the thermo switch starts acting up. Bleed to system before doing anything else. Air released then will explain the erratic behavior of the thermo switch.

[CorvallisBMW]

You buying factory or aftermarket? I had 2 switches from WorldPac fail closed, so the fan was running all the time.

I get mine from Blunt, OEM. But I suppose you can always get a bad part

You have to submerge it in boiling water and test it out with a meter. I had a similar problem that ended up being bad connector contacts. I ended up buying new terminals and connector. Apparently, this is not uncommon.

Good to know. i'm going to go over every wire and relay in the system with a fine-toothed comb.

Using a vacuum fill system eliminates any need to bleed the system and is the best way. But using the correct bleed procedure (see below) works almost as well.

1) Using ramps or a jack get the front of the car 1' or more higher than
the rear. That will make the radiator and bleed screw the highest point
on the engine and facilitate removal of air.

2) With the bleed screw open, add coolant until no more air comes out of
the bleed.

3) Leave the filler cap off, or at least loose, and set the heat for max
temp and fan speed. Leaving the cap loose will prevent air that's still
in the system from causing a "coolant fountain" once the engine heats
up. Start the engine and allow it to warm up to operating temp. As it
warms up occasionally crack the bleed screw to release any air and top
up the coolant as necessary.

4) Once the engine is at temp bring it up to 2000-2500rpm for a few seconds
several times. Then crack the bleed until no more air is released. At
this point the heater should be throwing lots of hot air, which
indicates that the heater core is filled with coolant. You may have to
repeat this a few times to get all the air out.

5) Drive the car a bit, allow it to cool back down, and recheck the
bleed for air. Over the next few days you may get very small amounts (a
few bubbles) of air out of the bleed screw.

After fully bleeding the system, drive the car for a few days and re-bleed. Release of a significant amount of air then or later is evidence of ahead gasket leak. And if the thermo switch starts acting up. Bleed to system before doing anything else. Air released then will explain the erratic behavior of the thermo switch.

The only problem with this method on my car is that if I raise the front of the car too high, the radiator sits higher than the bleed screw (which is on the thermostat housing)

[CorvallisBMW]

Going to bump this again!

I'm still having similar issues with the fan switch, and I'm also noticing a significant difference in where the temp gauge sits while cruising on the freeway vs in town. Supposedly the thermostat is 80C, but the needle sits at the first hash mark when cruising on the freeway when the ambient temp is less than about 75F. But if I'm in town, or the ambient temp is higher (80F or more) then the gauge sits closer to the middle. And the fan doesn't kick on until it hits the middle either, even though it's supposed to come on at 80C as well.

I'm also smelling coolant when I first turn on the heat, and just yesterday when I moved the car after letting it sit for about 3 months, I noticed 6-8oz of coolant in the drain pan.

Could poor pressure in the system, caused by leak in the system from somewhere around the heater core, cause symptoms like this? And would a pressure test be the best way of detecting a leak?

[jlevie]

Are you still getting air out of the system on a bleed? That is evidence of a head gasket leak. The heater core is a different matter. It is leaking and needs to be replaced.

As to bleeding. Disconnect the small hose that goes to the top radiator and blow into it with the cap on and the bleeder closed after bleeding the system until fluid comes out of the radiator.

[CorvallisBMW]

I still get small amounts of air, but it's not much. I had the coolant checked by a shop for hydrocarbons and they said none were present. I was hoping that ruled out the HG but I suppose it's still possible.

I hadn't tried that trick with the small hose but I'll give it a shot. I'm going to rent a pressure tester as well and see what, if anything, it shows me.

[jlevie]

While a positive test for hydrocarbons means there is a head gasket leak, a negative result doesn't mean that there isn't a leak. Once fully bled in the absence of cooling system work there should not be any air released on a bleed. The only way air can get into the cooling system is from a head gasket leak.