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oil cooler fan t'stat and switch installation

Hi Folks,

I get stuck sometimes (often) on the way back home from work in the miserable traffic on 101 across the GG bridge and in the summer it can get pretty hot. It kind of pissed me off that the fan on my 87's front cooler would never turn on, so I decided to do something about it. In all my time of owning the car, I'd never heard it once.

I've read that the factory's t'stat only turns on the fan at 244F, which is way too hot, considering that there's probably a 20-30F temp difference between engine oil temp and temp at the cooler itself from heat transfer along the lines.

I'd read somewhere here that there's a BMW t'stat rated at 194F with the same thread pattern that can be installed, so I ordered one from our host and installed it. It's kind of a b!tch actually...

I put the car up on the lift and pulled the R front wheel to have a look. You need to remove the horns and their bracket, which is held on by three 13 mm bolts, one of which attaches to the bottom of the headlight bucket. It helps to remove the wiring from the turn signal and running light, and the aluminum reinforcement bar which runs along the inside of the bumper as well, which is held on by two long 13 mm bolts.

With this business out of the way, and your eyes full of grit, you can being wrestling with the cooler. It's held on by three 13 mm nuts. Two on rubber-isolated mounting studs at the bottom, and a third at the top. I removed these, as well as the oil cooler line brackets in the fender well, but couldn't get enough movement to wiggle it off the supporting studs on the bottom. Finally after much cursing, I managed to pry it off there by using a large screwdriver between the cooler and the lower mounting bracket.

Here are the two t'stats. The BMW part is on the left. Note the shorter extension of the temperature sensing element. Doesn't seem to have caused a problem.



Here's a view looking up at the t'stat after installation. Note Porsche's strange arrangement of the ground connection, which is actually mounted on the cooler itself, while the power connection with the blue wire has the odd cylindrical connection pictured dangling in the front. BMW uses the more traditional spade connectors, and has both connections on the t'stat itself, so the power connection had to be modified to fit.



When you go to replace the cooler, I recommend you slot the lower mounting holes in the cooler like this with a dremel or whizz wheel to avoid the pain of trying to pry the whole thing back into place again. Why didn't Porsche do this? You can see the scars from the original removal:



My sealing gasket around the periphery of the cooler was pretty much non-existent, so I ordered a foam seal for an aircooled VW bus. This part fits the 72-79 type II, and is used to make a seal between the the engine tin and the body. It's slotted on either side, so it's a pretty good fit. It was about $35, and best of all, it's about twice as long as needed, so if you screw it up, you can try again:



After finishing, I finally heard the thing go on in traffic a couple weeks later when there was an accident on 101 and I'd been idling for a half hour or so just creeping ahead on quite a hot day. It finally turned on around 220-225F engine temp.
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Last edited by ianc; 11-05-2006 at 08:02 PM..
Old 11-04-2006, 07:14 PM
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I have the opposite problem. My fan will not shut off. I've disconnected the wire until I can change the thormoswitch.

I have a new one from pelican and actually tried to change it once but didn't think I could get enough movement in the oil line to change it.

You were able to change it without disconnecting the oil lines?
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Old 11-04-2006, 07:25 PM
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Not satisfied with that, I decided that an additional manual switch to turn on the fan would be useful. I thought for a bit about the least obtrusive way to do this, and hit upon the idea of using the rear windshield wiper switch. The car used to have the rear wiper when I bought it, but when I ditched the tail, that went with it, leaving me an extra switch.

In order to do this, what you essentially have to do is ground the fan relay by means of the switch. I looked around for a way to do this near the relay panel, but couldn't find an easy way to do it without splicing into the wires themselves, and one of my electrical mantras is never to touch the factory wiring if it can be avoided.

The first actual interruption in the wiring from the relay to the t'stat is in the front right side of the trunk near the spare:



I reasoned that if I could find an identical connector, I could just fabricate a short connecting piece with an additional branch to run to the switch, and that would leave the original wiring intact. After a bit of searching around at my friend's shop, I discovered just the thing. Here's the connector I made with the yellow wire as a take off to the switch. The covered blue spade connector joins to a wire running to the switch. Underneath you can see the black bakelite connector for the fan's actual power supply and ground wires:



Here you can see the itinerant yellow wire making its way rearward behind the relay panel and back behind the dash:



Here it is emerging from the hole in the dash. The rear of the switch becomes much more accessible with the removal of the wheel and the oil temp\press gauge:

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Old 11-04-2006, 07:37 PM
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After checking, I found there is continuity between the top two terminals of the switch when it is pressed down. To complete the installation, move the ground wire from the lower right terminal to the upper right, then remove the upper left connector from its terminal, and substitute the yellow wire in its place. Zip tie everthing in place for neatness:





And here's what the end result looks like; just as stock, and an installation that can be removed later if necessary with no cut wires, etc.:



Next will be to box in the bottom of the cooler with a piece of scrap aluminum or plastic as Chuck did, but I guess that can wait until next summer.

Hope this helps someone!

ianc
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Old 11-04-2006, 07:42 PM
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D'oh! Don, I know somone would get in there before I finished.

Quote:
You were able to change it without disconnecting the oil lines?
Yes, actually. It was a bit of a struggle to pry it off of the bottom bracket, but it can be done.

Easier for you might be to mount a manual switch as my posts after yours show though.

ianc
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Old 11-04-2006, 07:44 PM
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Ianc,
Can you provide a part number or link for the BMW tstat?

Thanks!
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Old 11-05-2006, 07:27 PM
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Quote:
Can you provide a part number or link for the BMW tstat?
Hi Mark,

Yes, negligent of me not to have included it earlier. The part description is:

Auxiliary Fan Switch 2-Prong (White Top) 91 Degrees, 318i (1984-85), 325i/is/iC/iX (from 08/87), M3 (from 02/87), E12 528i/530i, E28 5 Series all, E24 6 Series (09/82-08/86), E23 7 Series all

Part # is: 61-31-1-364-272-91-M36

and cost was $13.75 from our host,

ianc
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Old 11-05-2006, 07:52 PM
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good read. thanks
Old 11-06-2006, 04:28 AM
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Good write-up Ian.

To put it in oil temp gauge terms . . .



Ian
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Old 11-06-2006, 04:59 AM
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Thanks for the switch detail ianc. I'm going to order the part now and add the project to my list. I appreciate your time and effort on the research and how to!
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Old 11-06-2006, 07:28 AM
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I am looking forward to reducing oil temp. in hot conditions. Looking at the picture of the BMW part...are the threads the same?

Vytenis

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Old 12-31-2006, 06:21 PM
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Yes, they are....
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Old 12-31-2006, 08:59 PM
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Look here... I found a lit switch ( choice of amber, red or blue) that fits perfectly and is cheap..about $3 at the NAPA store...

Factory looking switch for OIL cooler fan.

- Wil
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Old 01-01-2007, 08:42 AM
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Greetings to all...came upon this dated thread and wanted to ask for some clarification.


ianc: When you state "In order to do this, what you essentially have to do is ground the fan relay by means of the switch.",...where is this fan "relay" you speak of located?

Thanks, in advance.

Best,,

Mine is a 89 coupe (SA Edition), 3.2L. I've long removed the rear wiper and have made temp use of the console switch to operate the aux fan manually. I wanted to ensure that the grounding path fires through a upper current rated relay contacts
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Old 05-06-2007, 12:23 PM
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Well,..further searches have revealed more data..(and maybe confusion)

Bentley 970-33, I assumed to be for the fan at the rear... w/ relay #2 /fusebox being the driver...Am I reading this wrong? I assumed they would state AUXILLARY oil cooler in the print (not "oil" cooler)..guess a tracing of the wires would provide "light"...

Please slap me around with the facts..

Best,
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Old 05-06-2007, 12:31 PM
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slick idea and work, ian.
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Old 05-06-2007, 01:01 PM
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further searches reveal that relay #2 is, in fact, the relay to fire the aux fan.....Amen?

No need for an additional relay in a 1989!!

Best
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Old 05-06-2007, 01:29 PM
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Hi dshepp,

Yes, there is already a relay for the cooling fan in place. Can't remember off the top of my head which one it is, but it lives in the front relay panel. Normally this relay is grounded by the thermostat I replaced in the the oil cooler, but you can do this by means of a switch instead (or in addition to). When the switch is pressed, the relay is grounded turning on the fan. Have a look at the wiring diagram in the Bentley for more info. HTH,

ianc
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Old 05-07-2007, 09:05 AM
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Thanks, ianc. I'm a EE and have installed a few electrical mods to the car already. I just can't believe I missed this when I planned out my mod. Having removed the rear wiper, easy enough to make use of the console switch...providing ground to a relay I installed to drive the fan. There was no need for the additional relay, as your thread revealed . It must be relay #2 (the only one labeled oil cooler fan) living in the area you suggested. I guess (in my early days of ownership) I assumed this relay to fire a fan in the engine area... oh well.....guess I'll leave her alone, as she's doing fine (as designed)...

Headlamp switch mods were great, too. BIG improvement!

Thanks! AND BEST!!!
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Old 05-07-2007, 09:25 AM
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Question I'm not sure what I'm doing wrong. Electrical is not my strongest point.

Fan used to run all the time when the car was on. Now it never comes on when car running. I'm thinking bad thermostat.
I first checked fuse and relay (swapped the relay with the cruise relay and cruise still operates). Both good. Check.
Next I ran power from the battery to the brown and teal wires on the lower connector in the trunk. Fan comes on, check.
Next I put a meter into the connectors with the ignition switch on. Power, check. Put meter into the gray/teal side and grounded the other lead and got power reading on meter.
So shouldn't the fan have come on when I grounded the power side (in essense the same as running a ground thru the wiper switch)?
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Last edited by Por_sha911; 09-02-2010 at 04:13 PM..
Old 09-02-2010, 03:35 PM
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