Auxiliary Fan Temp Switches

[1st 5er]

I need part numbers and/or advice.

I've been working through some symptoms and find my self looking for what I think might solve this problem.

With the key in the run position both sets of wires leading to the temp switches in the radiator housing are hot.
The fan will come on in both the low and high mode depending on which set of wires I short.

I've installed an E28 radiator with the E12 temp switches.

When heating up the switches manually they close the circuit and activate the fan, but when installed in the radiator they do not.
Is this possibly because of the plastic radiator housing or maybe how high they set on the radiator housing, or are the switches just bad.

I've not been able to find the part numbers for said switches, so some help there would be appreciated, and/or is replacement not the solution?

[Mike W.]

http://www.realoem.com/bmw/showparts.do ... g=17&fg=05

Scroll down a ways and they're there.

One question though, was the radiator new? I've found some restricted radiators pass the coolant slowly enough that it's cold by the time it gets to the switch side, so the aux fan never turns on. The coolant that gets thru is cool, but there's not enough of it to keep the engine cool. which sounds like what might be happening to you. Also keep in mind the old radiator test, get it good and warm, then shut the engine off. Then open the hood and feel all over the radiator. It should be hot everywhere, cold spots mean limited flow, and to properly cool, it needs good flow all thru and across the radiator.

[Robert Bondi]

You might also check the aux fan relay. In a few situations in which
I expected the aux fan to be on, I pulled the relay out of its socket and
stuck it back in - fan starts. There's also a 25A fuse.

[1st 5er]

http://www.realoem.com/bmw/showparts.do ... g=17&fg=05

Scroll down a ways and they're there.

One question though, was the radiator new? I've found some restricted radiators pass the coolant slowly enough that it's cold by the time it gets to the switch side, so the aux fan never turns on. The coolant that gets thru is cool, but there's not enough of it to keep the engine cool. which sounds like what might be happening to you. Also keep in mind the old radiator test, get it good and warm, then shut the engine off. Then open the hood and feel all over the radiator. It should be hot everywhere, cold spots mean limited flow, and to properly cool, it needs good flow all thru and across the radiator.

Thanks for the #'s.

Nope, not new radiator.
Did the "old radiator test". Hot to the touch on the driver's side, cold on passenger side.

Am now doing a chemical flush, using an over the counter product, that'll hopefully work and keep me from having to pull it again.
But, if I have to, no biggee. I like working on my car.

[Mike W.]

Am now doing a chemical flush, using an over the counter product, that'll hopefully work and keep me from having to pull it again.

That might work, but probably not, don't expect much. Sounds like it's radiator time.

[1st 5er]

Am now doing a chemical flush, using an over the counter product, that'll hopefully work and keep me from having to pull it again.

That might work, but probably not, don't expect much. Sounds like it's radiator time.

You're more than likely right, I've driven probably close to 3 hours with the cleaner in there with only slight improvement, the passenger side is now much hotter than before, but the fans still don't come on.
I'll swap with one of my E28's later in the week if the fans don't come on, and see if that does the trick, if so I'll then see about having this one professionally cleaned.

[Karl in KS]

A radiator flushing trick I discovered by accident: The large hose from the expansion tank back to the engine is a slip fit over a garden hose. So after draining the old antifreeze--disconnecting the lower radiator hose--I fastened garden hose to that return hose from the expansion tank and turned on water till it started to trickle out of the lower hose port on the radiator. Then I started the engine and ran it for a while. The hot water may help your radiator flush.

BTW I had the original radiator recored at a local shop run by an old timer who knows how to do these things, and have no problem keeping the temp of that 3.5L engine under control.

[1st 5er]

So, here's what I've gotten to.
Running the flush didn't change the temp gauge readings significantly, if any at all.
When driving it'll stay just off the right of the center mark, but at idle it moves about 1/2 way towards the next mark.
The cooling fans still do not come on, as there is about a 40% reduction in temperature from the inlet to outlet side of the radiator at the top and about half that at the bottom outlet.
I next swapped a radiator out of my E28 535i and the same result.
I pulled the temp switches and looked in the openings and the radiator is as clean as a whistle in side.
I'm assuming the radiator, fan and clutch are doing their job.

Due to high southeast Texas summers, I'm going to switch to the 71 Degree C thermostat and since everythig else is known good and functioning when tested as it should, I'm going with the way T.Hanson put it, let

the needle stops where it does and that's that.

In passing, and don't know if this'll make any difference, but I'll mention it.
The coolant reservoir, I discovered, height setting is adjustable.
The forward mounting bolt was loose and had allowed the reservoir to drop to it lowest level.
I raised it to it's highest position and secured the mounting bolt.
Don't know if this is really significant as to water volume in the system, just thought I'd mention it.

P.S. New cap went on the reservoir.

[Brian Smith]

It could be that your guage is not getting the right signal.
If you have the resistance curve for a particular sensor, you could attach an ohmeter directly to the sensor with its leads removed and see if the reading corresponds with the reading on the in-car gauge.
Secondly, since the problem is particularly present at idle, perhaps your water pump is not completely doing the job. I know that for some people with e28s it seems that the wrong brand pump is the difference for them between being in danger of overheating or not even close.

Maybe swapping the known good pump along with the known good radiator would end the confusion.

[Mike W.]

71C stats are a common attempted solution to running hot, but they don't do much. If a car is running hot or overheating, the stat is fully open anyway, the only thing it will do is sometimes give you just a minute or two more time before it would overheat.

Times like this a temp gun can be handy and they're not too expensive anymore. Even if you don't know exactly what they should be, you can compare them to another car.

There are a couple of other possibilities. Bad grounds are a notorous problem with temp gauges. Is there any difference when you turn on the turn signals or the heater blower or wipers? If so, run an extra ground between the body and the engine. And where does the needle sit when it's stone cold? I had an E24 one time that always ran hot, but never overheated. Even after I got the ground situation sorted out, it was always hot. Then one day I noticed, first thing in the AM, the needle was almost at the top of the blue, before I even started it. I took it out and that was as low as it would go, but moving it by hand it would go way past the red. I removed the needle, not easy, but doable, and repositioned it so the range of travel was equal, it would to or just past red on the high, and to or just past the blue on the other end. Set the needle there and all was fine, suddenly it was no longer running hot, LOL.

[1st 5er]

It could be that your guage is not getting the right signal.
If you have the resistance curve for a particular sensor, you could attach an ohmeter directly to the sensor with its leads removed and see if the reading corresponds with the reading on the in-car gauge.

Some numeric details here would be helpful.
I've grounded out the lead going to the sensor and it pegs the temp gauge to the right.

Secondly, since the problem is particularly present at idle, perhaps your water pump is not completely doing the job. I know that for some people with e28s it seems that the wrong brand pump is the difference for them between being in danger of overheating or not even close.

Maybe swapping the known good pump along with the known good radiator would end the confusion.

Tell me about a bad water pump.
I was under the impression that seals or bearings were the typical failure areas.
How does one determine impeller failure?
The radiator is good, as best I can tell, see above comments. Unless all three I've tried are bad.

[1st 5er]

71C stats are a common attempted solution to running hot, but they don't do much. If a car is running hot or overheating, the stat is fully open anyway, the only thing it will do is sometimes give you just a minute or two more time before it would overheat.

Times like this a temp gun can be handy and they're not too expensive anymore. Even if you don't know exactly what they should be, you can compare them to another car.

I get your point on the thermostat.

My IR "temp gun", though mine isn't shaped like a gun, reads at the temp sensor 195 +/- when fully warmed, and this is when the gauge needle is about halfway between middle and the next line to the right.
What is the normal acceptable range?
Has anybody done an E12 graphic like this one for the E28?

There are a couple of other possibilities. Bad grounds are a notorous problem with temp gauges. Is there any difference when you turn on the turn signals or the heater blower or wipers?

And where does the needle sit when it's stone cold?

The only change with any electrical usage is when turning on the headlights. It bumps maybe half the width of the needle towards the hot side.
Absolutely no movement at any other time.

I installed new battery to motor, battery to body and motor to body ground straps and nothing changed.

"Stone cold"? This morning's outside air temp is about 75 and the needle, with the key on in the run position, is just south of the blue.

Based on the above pic of the E28 temp gauge readings it looks as if I'm OK temp wise, assuming the E12 is within the same range.

[Mike W.]

About bad water pumps. I have seen, not on a BMW, but a 47 Cadillac, where the impeller came loose from the shaft so it was barely turning and not pumping water. And later BMW's, as in E39 or so and newer, use plastic impellers that can break apart. But I've never seen one of them on a M30 engine. So I doubt the water pump is your problem, though a heavy duty one like the GMB with it's larger impeller can pump more water than a stock one.

But enough of that. Since you have a temp gun, even if it's not gun shaped, LOL, compare it to your E28, they're both M30's, so the temps should be similar. If they are you're good, if not, then pursue it. It's also an option when troubleshooting, you can compare the sending unit resistance between the two.

[Bruce]

A bad water pump can definitely cause it to run hot. At about 50,000 miles, my original pump died and left me stranded on a trip. I made it to the nearest BMW dealer at the time. I just recently had an over heating problem. I thought a noise coming from the engine compartment was the air pump. Not so! I took hold of the pump pulley and could move it back and forth perpendicular to the shaft. I replaced the pump with an after market pump, and though it's not over heating, it still runs warmer than it did (like half way between 12 o'clock and the red mark instead of straight up). I'm considering replacing the pump with a BMW pump. I bought this one off the Internet and assumed it was a BMW pump. I haven't gotten around to replacing it yet.

[1st 5er]

Compared to my E28 eta, running temps, per the IR "gun", are within 5 degrees F of each other, although my ETA gauge runs left of center and the E12, now, just right of center.

I'm satisfied with the temp readings from the "gun" and think that based on my diagnostics that the aux fan will come on when needed.

My water pump may be original, not sure, but it doesn't leak, make noise, or have any play in the shaft whatsoever.
If it ain't broke, I don't usually mess with it, because I usually have plenty of broke stuff to mess with.
My driveway looks worse than Mike W.'s.