Re: 533i Over heating

["D.S." <dasquestbox@xxxxxxxxxx>]

My advice is to do try a cheap solution first.  Drain the coolant, take out the
radiator and give the fins a thorough cleaning.  A pressure wash sprayer works
best.  You can also use a self service car wash sprayer to avoid  renting a
pressure sprayer.  A high pressure stream from my garden hose worked for me.
Repeated overheating tends to stress the thermostat element so it might be
worthwhile to replace it while the coolant is drained.  Even if you don't have a
major cooling problem, cleaning the fins will help any high mileage vehicle run
better that has the original radiator.

D. A. Smith

> I had very similar problems with my '87 535is.  I took the "replace it all"
> approach (except for the radiator) and ended up with a temp needle that
> never exceeds halfway even with the AC on sitting in traffic on a 90+ day.
> I replaced the water pump, all water hoses, thermostat (went from stock temp
> to 71 degree version), and both radiator temp switches.  In the case of the
> temp switches, I bought a lower than stock temp switch for the low speed
> position and put a new stock low speed switch in the normal high speed
> position.  All this did was cause the fan to kick on at a lower temp and go
> into high-speed mode at a lower than stock temp.  The new lower temp switch
> and the non-standard thermostat were sourced at BMP.  In addition to all the
> parts, I also flushed, re-filled, and bled the cooling system.  Normal
> needle position is around 11 o'clock, but I haven't seen it above 12noon
> since doing the above.
>
> You indicated that your fan doesn't kick on until the needle is near the red
> zone...  The ballast resistor mounted to the fan housing may have failed
> which would prevent the fan from kicking into low-speed mode even if the
> temp switch in the radiator is working properly.  Bentley can help with
> diagnosis, but essentially you jumper the two wires going to each temp
> switch to see if the fan will work at both speeds.  If it does, then your
> temp switches are likely shot.  There's just tons more info on this subject
> out there.  Good luck with the search on the problem.

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