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Discussion Starter #1 (Edited)
:confused:Hi there, I need help!
The water pump on my 91 M5 (S38) went out and started loosing coolant from the weep hole on the pump. I replaced the water pump and now the temp gage goes to red within 5 minutes (driving or idling). I figured the thermostat might have gone bad, so I replaced it also.
It still gets hot within 5 minutes. Could it be that the fan belt is too loose? it's not slipping! I also noticed that my aux fan is not going on. Could that make that much of a difference?
Any help and suggestion would be greatly appreciated.
Thanks in advance.
Vafa
 

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Did the car overheat before you changed the pump?? if not, then I would suggest that you have an air lock in the cooling system. Bleed the system thoroughly (max temperature for heating, motor running, open bleed etc)

If the engine has overheated, then I don`t dare to say what I fear out loud....

The aux fan does not do that much of a difference when the car is rolling. mostly idle. Does your cooling fan in the engine compartment engage? though this too is mostly important in city traffic/idle.

SAkke
 

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always remember to use good cooling/anti freeze liquid.
 

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We kinda need to know if the car fully overheated before you replaced the pump to help diagnose the new issue after you replaced the thermostat and pump. Also did you let the car hit the red when it started to overheat or did you cut off the engine before. Best case scenario like DrSakke said you have air lock and simply need to bleed the cooling system off, worse case when you overheated the car you warped the head which is allowing combustion gases to leak into the cooling system. Good luck and keep us updated.
 

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Discussion Starter #5 (Edited)
overheating problem

Thank you all for your help and replies,
I had no overheating issues at all prior to the pump going bad, the water pump went out rather suddenly, loosing coolant from the pump itself. Luckily it was in front of my house and the temp gage got hot but never into the red, as I shut down the engine as soon as the gage moved to near red zone.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com
clogged. Is there a way to find out if the flow is restricted or not?
Also is there an aux pump? I've seen it at some online part stores.
<o:p>Again, thanks for the replies and any suggestion is appreciated.

Vafa
</o:p>
 

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the aux pump is mostly for heater function, it's mounted below the heater control valves, by the air bleed screw.

If the radiator is original, it could certainly be bad, does the car overheat idling in the driveway or only on the move? If you turn the heat up to full, can you delay the onset of overheating?
 

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Discussion Starter #7
overheating problem 91 M5

I can't remember when the radiator was replaced, it was along time ago!
But I had no problem with overheating prior to water pump going bad. would the radiator suddenly go bad or gradually over time?

The car overheats in idle and while driving only two blocks, but it cools back very quickly, in 2-3 minutes. and that's kinda strange! (It goes to red in 5 and back to normal in 2 minutes)

I haven't tried running it with the heater on. I'll try it in the morning.

Thanks,
Vafa
 

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Discussion Starter #8 (Edited)
I have one more question,
the repair manual is not clear, but it seems as it indicates that after flushing and replacing coolant, one would need to run the engine at 2500 RPM With the expansion tank's cap off till the level steadies then replace the cap!
Is this correct? how about when bleeding the system. should the cap be off or on?

Thanks,
Vafa
 

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Hi!
When the pump went bad, was it intact or was there loose parts? is so, something could have gone further inte cooling system and blocked the system??? Cools down fast-is that while driving on a higher speed ,or do you turn off the car and wait???-be precise! In the last case I would suggest block in the channels-air or something else...

:cheers:
Sakke
 

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Silly question, but is it really overheating?

Check the connection to your temp gauge sender. I had a fluctuating temp gauge and a fiddle with the sender fixed it.

If i recall correctly there are two sensors, one for the ECU and one for the gauge. So the running of the car of not affected when the gauge plays up.

Number 13 I think.

RealOEM.com BMW E34 M5 3.6 Cooling System Water Hoses
 

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Discussion Starter #11
DrSakke,
Cooling down fast when engine is off waiting for it to cool down, if I don't shut down the engine it continues to heat up to red mark.
I tried driving to get fresh air to the rediator, but it still gets hot very quickly.
The waterpump looks intact, I don't see any metal shavings around the old pump.

Vaf
 
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