RE: reply: E24 overheating

["Aaron Bohnen" <bohnen@xxxxxxxxxxxxxxxx>]

Hi Piers, (hope you don't mind me copying this to the digest - there may be 
others who might be interested)

Thanks for the mail:

> *	Your relays must be different than mine

Not necessarily.

> *	When I jump the two wires on the high temp switch  together with the
> IGN on, I feel the relay K6 click and the fan goes on.

Sounds right - same here.

> *	When I jump the two wires on the low temp switch  together with the
> IGN on, I don't feel any relay click, the fan goes on and I can feel the
> ceramic ballast resistor adjacent to the aux fan click. The K1 relay is
> supposed to click, I believe, but when I switched it with another from the
> fuse box there was no difference.

Well, as long as the fan is responding to the control signal from the 
switch correctly I think all is likely well with it. I wouldn't worry too 
much about the relay since the fan seems to be acting appropriately.

> *	If I hot wire (with a positive lead from the battery)  one prong of
> either switch the fan turns at the appropriate speed.

Sounds right - you're just putting battery voltage to the control system. 
Seems to me that it should work this way.

> *	If I hot wire the other prong the interior blower fan and the seat
> belt idiot light and chime go off - go figure?

Weird - can't quite figure this out except that maybe the applied voltage 
to the switches from the control system is less than 12V - and when you 
apply 12V to them it snazzles (good word, eh?) some other aspect of the 
control system enough to fire up the interior fan and idiot light. Under 
these circumstances I'd probably refrain from doing that again.

> *	After playing around for a while something got too hot, maybe the
> ballast resistor, and nothing worked.
> *	What ever it was seemed to cool off and I was back to my original
> situation.

That's good!
 
> My conclusions:
> 
> *	I probably need a new high and low temperature switch.

I'd replace those with the 81 and 88 degree (rather than stock 91 
and 98 degree) switches from BavAuto - or check your local OEM supplier for 
suitable units. You probably want that fan to switch in earlier given the 
likely age/condition of the radiator and the fact that the switches are in 
a totally stupid location on the rad - one in which they might never even 
see coolant if your level is even slightly low.

> *	I may need a new ballast resistor

I certainly need one of these - mine was jumpered by the previous owner. 
Both fan switches run my fan at high speed. This is fine with me so I 
didn't change it.

> *	I may need a new KI resistor

Well, if the control system works I'd say leave the K1 relay alone. And if 
you do put another one in there, don't go and buy it from BMW - they'll 
fleece you for what is really a simple automotive relay. Just get yourself 
a Bosch or Hella unit with equivalent pinout and current rating from your 
local supplier.

> Please comment.

My comment after all of that is good luck! Check your switches - ie: put 
them in a saucepan with an accurate thermometer or gently warm them up 
with a torch in a small can of just enough water to cover them (don't touch 
the switch with this - just the can!) and then test them at the 
appropriate temperature. No reason to replace them if they're working fine 
unless you want to go with the lower temperature switches as I'd suggest. 

Additionally, you might also want to check your coolant level. If it's low 
you may have the situation where the coolant never reaches the switches. 

Finally, (and this is something I'm considering myself) I'd think about a 
two-position manual override switch in parallel with the fan switches at 
the front of the car. The system would continue to work as designed (and if 
the aux fan was switched on by the system you wouldn't be able to turn it 
off) but you could also have an option to power it on to low or high 
yourself from inside the cabin. If the system's working well this will not 
be necessary, but if there's still any doubt left or if you are worried 
about losing some coolant to the point where the switches are not fully 
immersed in it, such a manual override might be worthwhile and valuable 
peace-of-mind insurance.

best of luck!

Aaron
___________________________________________________________
Aaron Bohnen                     email: bohnen@domain.elided
- -Ph.D. Student, Civil Engineering Department, U.B.C.
- -Technicraft Engineering Services

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