Re: E24 overheating/E28 experience

[rusmaster <rusmaster@xxxxxxxxxxxxx>]

I'll jump into this fray with my experience.  Looking at the fan can be a source, but with that age
of the car I'd look at the radiator and expansion tank also.  The OE radiators are notorious for
clogging and the expansion tanks are known to flare out on the lips that hold the cap tight for
proper pressurization of the system.  My E28 has had/have both problems.  I've also heard this with
other owners as well.  I replaced the radiator and have still to replace the ex. tank.  In my case
you can see how the lip has bowed, especially where the cap flange is always pressed against the
plastic lip on the tank in the fully sealed position.  Mine I believe was made worse by a serious
over-heating of the car after an accident.  But they can still fail.

These can be easily checked by any repair facility.  The radiator can be checked by using a temp.
sensor to see if there are variations in temp. along the surface of the radiator.  The tank is
about $60 and is good protection just to replace on high mileage/older cars.  Also do a pressure
check on the system to see if it can hold pressure properly.  If it can't, this can cause the
problems your seeing also.  I don't know if you have the aluminum/plastic radiators, but the seal
from the core to plastic ends are know to leak over time.  Especially if the car has been
over-heated.  In my case the seal had been leaking for some time, yet showed no signs of leaking,
yet I was slowly lossing coolant.

Agian, I'd have a repair shop check the radiator and do a pressure check of the system if the
switchs work OK.

OH, a note on the temp sensor in question, BMW put the switchs in a terrible place high on the
radiator.  Unless the system is working in top condition with proper coolant level and
pressurization and has been proper bled, the coolant won't make contact with the sensors high in
the radiator.  In turn they don't sense the temp. of the coolant and don't turn on the fan!!!!
This was a failure mode in my E28.  This I believe is a poor design flaw and can cause lots of
problems in older/high mileage cars.  This is why I say it's real important t insure the system is
working properly first and then debugg the other less important fan systems after.

Take Care,
Russ
'88 535iS   Healily Dinazised

> Date: Tue, 8 Sep 1998 11:09:21 +0000
> From: "Aaron Bohnen" <bohnen@domain.elided>
> Subject: reply: E24 overheating
>
> Hi Piers,
>
> About your query and your overheating 6'er...
>
> > Any ideas? I have noticed that the auxiliary fan in front of the radiator
> > only comes on with the air conditioning. Is it supposed to come on when
> > the car is overheating? Sure would make sense if it did. If so where do I
> > find the sensor/relay/whatever?
>
> I have been through this recently myself with my 533i. There are two
> switches that turn on the auxillary cooling fan. They are located at the
> top of the passenger's side of the main radiator. The top one with the
> white body is the low speed switch. The lower one with the red body is the
> high speed switch. You can check them as follows:
>
> low speed, white switch should close at 91 Celsius (196 F)
> high speed, red switch should clost at 98 Celsius (210 F)
>
> You can check the operation of the auxillary fan relays by removing the
> leads from the above switches and jumpering them. The fan should run at low
> speed when you jumper the leads to the upper, white switch and at high
> speed when you jumper the leads to the lower, red switch.
>
> The relays are located under rubber boots adjacent to the main fusebox
> between the fusebox and the driver's side fender. The high speed relay has
> two red&green wires leading to terminal 30 of the relay, the low speed
> relay has a single red&green wire leading to terminal 30.
>
> All of this information is available in the Bentley service manual for your
> car - which is the very best $$$ you are likely to ever spend on it. You
> can contact Bentley Publishers directly at www.rb.com or call them at
> 1-800-423-4595, or just contact Steve D'G at www.ultimategarage.com - I'm
> sure he'd be happy to sell you a manual.
>
> best of luck with your overheating and with your car!
>
> Aaron

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