2004 Z4 2.5 overheating

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John256

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So far I have replaced the reservoir , thermostat, fan relay, and fan, still overheating when idling and the fan is not kicking in. Any ideas would be greatly appreciated as I am at wits end.
 
Would be worth looking at the water pump. These generally weren't a problem like the M50/52 but it is 22 years old so it's possible that the impeller's broken up or is slipping on the shaft.

Also try flushing the radiator out.
 
smorris_12 said:
Would be worth looking at the water pump. These generally weren't a problem like the M50/52 but it is 22 years old so it's possible that the impeller's broken up or is slipping on the shaft.

Also try flushing the radiator out.
Click to expand...
This

I had a cat that would overheat and the plastic impeller had left the chat
 
Look for corrosion

Check continuity before and after the plug

Does the fan turn when the car is running and AC turned on?

First is check for issues on that small green wire next is check the fan is still serviceable
 
I'm So sorry to have taken so long to get back to this issue, had medical issues in the family.
Just went out and tried, and yes the fan does come on when the AC is turned on. What does that indicate?
And thank you so much for the advice as this is my first glimmer of hope to resolving this issue.
 
Out of interest, since you've ignored comments of a mechanical nature, why do you think this is an electrical problem?
 
I am willing to concede that it might well be a pump, I am just hoping to not have to go that route. With my limited shade tree mechanic skills electrical just made more sense for me. If not the pump then what other mechanical issues should I consider? Not trying to offend actually pleading for advice.
 
I just couldn't see how a malfunctioning pump would keep the cooling fan from engaging,
 
You say overheating but what are the symptoms? Does the gauge shoot into the red? Is it spitting water? How long does it take to overheat? And, since we're still sitting about in our thermals, what's the ambient temperature in Texas at the mo (partly that makes a difference, partly we just want a reason to feel jealous.)

If the pump isn't moving water about it's possible the sender that controls the fan isn't seeing hot water. Or it could be expecting the mechanical fan to do more (I think the M54 still had one.)
 
To add more detail to my example of a failed impeller- I agree with @smorris_12 direction on this

Car would idle fine, there was basic flow of fluid around the system and I checked this looking at the pipes going in and out of the heater matrix inside the car (at the bulkhead)

But… when the car drove, it over heated. Straight into the red

Get your pump pulled out
 
bigwinn

Thread 'M54 cooling issue- RESOLVED: with learnings!'

Right I am scratching my head

M54 engine

Had what I assumed was an expansion tank small leak which was replaced. Then the car overheated and popped the top hose off. I assumed it was a poor fit- so fitted a better tank

Then just couldn’t get it bled to get hot air from the vents

I fitted a new thermostat thinking that may be stuck open but made little difference- still no heat at the vents

Popped the pipes off the back of the heater matrix- no fluid but managed to get a slow flow of fluid to the matrix and heat in the vents

Great! Out for a drive and it overheats again

I don’t...
 
bigwinn said:
To add more detail to my example of a failed impeller- I agree with @smorris_12 direction on this

Car would idle fine, there was basic flow of fluid around the system and I checked this looking at the pipes going in and out of the heater matrix inside the car (at the bulkhead)

But… when the car drove, it over heated. Straight into the red

Get your pump pulled out
Click to expand...
Just for my own curiosity... would the radiator still become hot to the touch, or does the water pump not working mean the radiator would still be ambient/cold?
 
It got hot- quickly especially when driving

As the cooling system was only working at a small % it wasn’t shipping the heat out of the system
 
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