Re: E34 525i M20 - Overheating only during standstill on a hot day

[alex.fadeev@xxxxxxxxxxx]

"Eugene Hoe" <eugene@domain.elided> wrote:
> My E34 525i M20 seems to ocasionally overheat when the car is at a
> standstill or stuck in a traffic jam on a hot day. When the car is 
> moving, its absolutely fine. The temperature gauge can reach as high as
> 3/4 way to the red spot on the temperature gauge.
 
Eugene,
Three possibilities come to mind:
1. your thermostat is stuck partially closed. When was the last time you 
had it replaced?
2. the viscous clutch of your mechanical fan is dead. When the engine is 
at the operating temp, try to stop the fan from spinning with a folded 
newspaper. If you succeed, the ~$60 fan clutch is bad. 
3. the low speed resistor for your auxiliary fan is shot. Have you tried 
shortening the right pins on the coolant temp harness to prompt the aux. fan to spin at low speed? Turn ON the AC. Does the 
electrical fan spin? If not, replace the resistor. 

> The last time I checked the high speed fan mode on the aux fan by manual
> bypassing it, it was working fine but noticed it didn't activate even 
> though the temperature reached 3/4 on the gauge. [...] So the conslusion
> was the radiator was blocked so had an entirely new radiator put in 
> several months back. Now the car operates much cooler when moving but
> at standstill the temp can still go up past half way point on the temp
> gauge.
> 
> Anyone got any ideas what else could be causing the overheating during
> standstill?. The logical reasoning would be the aux fan or the fan 
> clutch but had those checked and both the fan clutch and aux fan is 
> working fine. 

Check you thermostat.

> I was also told the aux fan should not kick into high speed mode 
> during normal operation, it only kicks in when the temp is really
> high like past 3/4 mark on the temp gauge. Can anyone verify this?.

I think the threshold is when the coolant temp reaches 99C. 


HTH,
alex f

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