Weird behaviour - temp sensor or thermostat failure ?

J

jnwright71

Member
Hi All,

Help please.

My Z has been behaving really weirdly tonight. I went out to play football and about 6 miles into the journey I noticed the temp gauge had started to rise. So I ran the heater at full blast to try and pull some temperature away from the engine and the gauge dropped immediately back to normal, but then the heater stopped blowing hot air and got progressively colder, then the gauge started jumping around and the heater started blowing hot then cold etc. Eventually the red warning light came on and the car beeped, but then the temperature gauge dropped straight back down to normal.

After football (1.5 hours), the car was still very hot and when I started it the temp gauge went straight to normal. I drove the first 6 miles without the gauge moving, but with the heater still fluctuating between hot and cold. Then the gauge started moving again and the heater temperature fluctuation became even more extreme. Even more bizarrely, the temperature started to rise when the heater was blowing hot and falling when it was blowing colder.

When I got home I scanned the car using a basic OBD reader and the are no fault codes, but again the engine seemed very hot. I've not touched the coolant, other than check it before I restarted the car to come home. Even after the 1.5 hours it had been sat, there was still some pressure and the coolant was hot and at the maximum level.

Ordinarily I would think this is an airlock, but I cannot see how air could have entered the system as the water level is fine and there are no signs of a leak.

Could this be a temperature sender issue or a faulty stat ?

Any advice gratefullly received as I am really concerned.

Cheers, James
 
The symptons you describe are overheating and it sounds like you got it hot enough to boil the coolant and cause pockets of air (air locks). These cars (SI) suffer from faulty water pump at 70k miles, which are electric and expensive.
 
Thanks Guys,

Had the car up on a ramp today and there were no leaks and coolant was full, so I ran the car up to temp but only the top hose to the header tank got hot, the rest of the system was almost cold. Therefore, it must be the pump as there is no coolant flow at all. Checked was a BMW Master Tech (friend of a friend) and he confirmed that the impellers on the N52 pump often become detached from the shaft which continues to spin, but the is no coolant flow.

So tomorrow I will try and source a new wp and stat and get some BMW antifreeze on Monday. I am thinking about going for a Pierburg pump and a Wahler or Mahle thermostat. Would these be OK, or is it OE all the way ?


Cheers, James
 
As has been said, sounds like the electric water pump but that should show on the OBDs - mine did!

I can't help with advice on options, but my local BMW specialist fitted OEM parts when he replaced mine - pump was £500 and thermostat another £100 (plus fitting)! Ouch! :x
 
Is there no on board measuring of flow? I would expect the car to know if the pump was running but now coolant was flowing.
I wait to be corrected but can't imagine that the OE unit would be made by anyone else other than Pierburg as they seem to be the only supplier. I use OEM parts over OE usually unless they're not available e.g. MANN filters as you're just paying double for the BMW stamp on the same parts.
 
Hi Scooba Steve,

I have been reliably informed that Pierburg make the OEM pump, so I should be fine getting this.

In terms of the car knowing the pump has failed and coolant is not flowing, then apparently not. Certainly there was no EML or other warning other than the temp gauge increasing. Having reviewed other posts and other forums, then it appears these just fail without warning and the driver needs to be vigilant to ensure the car doesn't seriously overheat which could wreck the engine - poor design !!

Cheers, James
 
jnwright71 said:
Hi Scooba Steve,

I have been reliably informed that Pierburg make the OEM pump, so I should be fine getting this.

In terms of the car knowing the pump has failed and coolant is not flowing, then apparently not. Certainly there was no EML or other warning other than the temp gauge increasing. Having reviewed other posts and other forums, then it appears these just fail without warning and the driver needs to be vigilant to ensure the car doesn't seriously overheat which could wreck the engine - poor design !!

Cheers, James
Click to expand...

You are quite right - I had driven 25 miles or so, stopped to refuel mine, left the garage and in no more than 2 miles the temperature gauge was in the red with the red light flashing, but no other warning signs.

It is a poor design, but at least it has a temperature gauge - E90s and E91s with the same engine don't even have that! :thumbsdown:
 
The reason I was told the gauge had been dropped was due to the speed it went into the red and that most people don't notice, where as when a red light suddenly appears they do.

The other issue with no gauge though is you can see if the thermostat is stuck open resulting in the car not getting up to temperature, which was the issue I had in my old 2.5si.
 
jnwright71 said:
Hi Scooba Steve,

I have been reliably informed that Pierburg make the OEM pump, so I should be fine getting this.

In terms of the car knowing the pump has failed and coolant is not flowing, then apparently not. Certainly there was no EML or other warning other than the temp gauge increasing. Having reviewed other posts and other forums, then it appears these just fail without warning and the driver needs to be vigilant to ensure the car doesn't seriously overheat which could wreck the engine - poor design !!

Cheers, James
Click to expand...

ECP have 30% off tonight until 9
 
Hi All,

I sourced a Pierburg pump and Wahler stat today - £290 all in. I also picked up some BMW antifreeze and fitted the lot tonight. All is back to working properly.

For anyone interested, this is an easy DIY, although I did have the benefit of the car being on a ramp. Total job took me 5 hours, including fitting a new Meyle expansion tank (these tend to fail, so as it was only an additional £38 and I had to drain the coolant anyway this made real sense). As a total novice I don't think 5 hours is too bad - 30 minutes of this is the bleed cycle and about 1 hour was to do the expansion tank.

In total this job cost me just £351 - very reasonable given the circa £700 horror stories on here. The Wahler stat and Pierburg pump are supposedly the same as OE BMW (although the stat has a composite housing, not aluminium like the original on the car).

If anyone wants to know more about the process, I will be happy to help.

Cheers, James
 
jnwright71 said:
Hi All,

I sourced a Pierburg pump and Wahler stat today - £290 all in. I also picked up some BMW antifreeze and fitted the lot tonight. All is back to working properly.

For anyone interested, this is an easy DIY, although I did have the benefit of the car being on a ramp. Total job took me 5 hours, including fitting a new Meyle expansion tank (these tend to fail, so as it was only an additional £38 and I had to drain the coolant anyway this made real sense). As a total novice I don't think 5 hours is too bad - 30 minutes of this is the bleed cycle and about 1 hour was to do the expansion tank.

In total this job cost me just £351 - very reasonable given the circa £700 horror stories on here. The Wahler stat and Pierburg pump are supposedly the same as OE BMW (although the stat has a composite housing, not aluminium like the original on the car).

If anyone wants to know more about the process, I will be happy to help.

Cheers, James
Click to expand...

Good result! :thumbsup:

Mine was one of the £800 horror stories! :evil: But as I only have an allocated parking space to work in (well, when the neighbours don't use it) I just couldn't face trying a DIY fix!

Now you can go and put some more miles on yours. :driving:
 
srhutch said:
The reason I was told the gauge had been dropped was due to the speed it went into the red and that most people don't notice, where as when a red light suddenly appears they do.

The other issue with no gauge though is you can see if the thermostat is stuck open resulting in the car not getting up to temperature, which was the issue I had in my old 2.5si.
Click to expand...

Quite see your point - I suppose their excuse is that the OBD probably logs low temperature, but why should you need diagnostic equipment to find out?

Much as I hate to praise any Stuttgart product (!) for a year or so I drove a Sprinter and although it had no temperature gauge you could find the actual temperature when you scrolled through the OBC.

Sadly I think BMW have short-changed owners with this approach - :sly2:
 
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