Overheating / Overpressurising (again)

R

Robin82

Member
The coolant system on my facelift is driving me mad! I previously had coolant leaks (I think due to the severe winter and degraded coolant expanding) I fixed a few of these and then stored the car as I didn’t have to time to sort it completely.

After pulling it out of storage it’s now overheating (again). I’ve completely bled the system twice to no avail. Pumped water through the system from the front mounted pipe to to try and clear anything.

I gave up and took it to a well trusted garage, to their credit advised they cannot pinpoint the cause and so do not want to replace all manner of parts and not solve the issue. They are also not overly confident with bmw cooling systems.

They did advise there is a split coolant housing (pinhole) which lies at the bottom of the engine block near the water pump causing the leak. Also advised it’s ‘overpressurising’ as one of the large hoses is rock solid and that I should take it to a bmw specialist/dealership to diagnose.

As this could be hugely costly, any ideas what this might be? Overpressure would mean air/gas getting into the system, but the mechanics were 99% it isnt headgasket. Could it be a blockage?

Any advice appreciated
 
The 2 N46 engine has a secondary water pump, mounted on the inner wing behind the MAF. If that is not running then water will not circulate properly.
Check it just in case.
 
The thermostat could be stuck shut. Fan not coming on? Are you getting hot air from the heater? This chap is quite good but you have to listen carefully. https://www.youtube.com/watch?v=2-hzGqBZRfQ
 
enuff_zed said:
The 2 N46 engine has a secondary water pump, mounted on the inner wing behind the MAF. If that is not running then water will not circulate properly.
Check it just in case.
Click to expand...

Thanks enuf, I know we’ve spoke about this previously. I’ll take a look.
 
raymond.harper said:
The thermostat could be stuck shut. Fan not coming on? Are you getting hot air from the heater? This chap is quite good but you have to listen carefully. https://www.youtube.com/watch?v=2-hzGqBZRfQ
Click to expand...

Ah ok. I’m surprised the mechanic didn’t pick that up. No hot air at all, just blowing cold. The temp gauge also doesn’t move in one direction, it wavers back and fourth until it finally overheats (well i dont let it obviously).
 
Still sounds like a blockage of some sort. Did you raise her into the air when bleeding? https://z4-forum.com/forum/viewtopic.php?t=115474
 
raymond.harper said:
Still sounds like a blockage of some sort. Did you raise her into the air when bleeding? https://z4-forum.com/forum/viewtopic.php?t=115474
Click to expand...
Hi Raymond, yes raised right up. I also attached a hose pipe to the front outlet on the engine block and ran water through the system to try and make sure.

I’ve ordered thermometer gun, looks like a logical way to diagnose issues. All pipes are stone cold apart from the large main pipe coming out the block and the bottom pipe from the radiator that runs to the stat, which is not quite as warm.

The coolant isn’t even getting to that other minor pump on the leftwing.

It feels like a blockage. I’m sure the pump is ok (it isnt electric). and I can feel some water moving through the bottom radiator hose.
 
From what I can work out, the thermostat is electronically controlled. A model-specific code reader should be able to detect a fault. This is quite a common engine https://www.e90post.com/forums/showthread.php?t=1798189
 
I had a similar issue with the one I had to change the auxiliary pump on.
Took me several attempts to bleed it fully.
Like you, most of the pipes were cold.
I jacked up the front end as high as I could but made no difference.
In the end I took a risk (suitably covered my arms and face and wore thick gloves) - got it running and then pulled off various hoses one at a time. Eventually, when I pulled the one on the block at the top front of the engine it seemed to shift an airlock and all was well.

The other thing you don't mention is whether the radiator is getting hot at all? Can you check it and see if it is hot in places and cold in others, which would indicate that it is blocked.
 
enuff_zed said:
I had a similar issue with the one I had to change the auxiliary pump on.
Took me several attempts to bleed it fully.
Like you, most of the pipes were cold.
I jacked up the front end as high as I could but made no difference.
In the end I took a risk (suitably covered my arms and face and wore thick gloves) - got it running and then pulled off various hoses one at a time. Eventually, when I pulled the one on the block at the top front of the engine it seemed to shift an airlock and all was well.

The other thing you don't mention is whether the radiator is getting hot at all? Can you check it and see if it is hot in places and cold in others, which would indicate that it is blocked.
Click to expand...

After 2 hours out there with it this afternoon:

With thermo gun after it was up to temp on the gauge - radiator hot 70-80c at the top and cooler towards the bottom (25c). Bottom pipe out of the radiator about 20c.

Following the actions you took I jacked it right up, ran it up to temp and then whipped the expansion tank cap off. Huge volcano followed and all previously cold pipes were now hot. Hot air the blew out of the interior fan for the first time.

So I thought great! Thats it. Unfortunately on refilling/topping up, the pipes returned to being cold and the engine overheated. I tried this a few more times to no avail. I then flushed the entire system removing various pipes from the block and pump. Refilled but no luck. :(

It is strange how those rear pipes got hot, perhaps it was because I had it jacked high up at the time. Perhaps the auxiliary water pump has gone, would this cause the engine to overheat though?

You mention the radiator, the differing temps would be normal? Cold at the bottom hot at the top?

Thanks for your patience guys!
 
Robin82 said:
enuff_zed said:
I had a similar issue with the one I had to change the auxiliary pump on.
Took me several attempts to bleed it fully.
Like you, most of the pipes were cold.
I jacked up the front end as high as I could but made no difference.
In the end I took a risk (suitably covered my arms and face and wore thick gloves) - got it running and then pulled off various hoses one at a time. Eventually, when I pulled the one on the block at the top front of the engine it seemed to shift an airlock and all was well.

The other thing you don't mention is whether the radiator is getting hot at all? Can you check it and see if it is hot in places and cold in others, which would indicate that it is blocked.
Click to expand...

After 2 hours out there with it this afternoon:

With thermo gun after it was up to temp on the gauge - radiator hot 70-80c at the top and cooler towards the bottom (25c). Bottom pipe out of the radiator about 20c.

Following the actions you took I jacked it right up, ran it up to temp and then whipped the expansion tank cap off. Huge volcano followed and all previously cold pipes were now hot. Hot air the blew out of the interior fan for the first time.

So I thought great! Thats it. Unfortunately on refilling/topping up, the pipes returned to being cold and the engine overheated. I tried this a few more times to no avail. I then flushed the entire system removing various pipes from the block and pump. Refilled but no luck. :(

It is strange how those rear pipes got hot, perhaps it was because I had it jacked high up at the time. Perhaps the auxiliary water pump has gone, would this cause the engine to overheat though?

You mention the radiator, the differing temps would be normal? Cold at the bottom hot at the top?

Thanks for your patience guys!
Click to expand...
Not sure the auxiliary pump would make all that difference. And of course the whole idea of the radiator is to reduce the temperature of the water, but I can't believe it drops it as low as 20c.
The fact you have managed to get hot air in the cabin suggests that there is still an airlock or something somewhere preventing circulation. But at least the heater matrix isn't blocked.
It would be interesting to fit another radiator to see if that is the problem.
I have a spare here, but I'm not particularly close I'm afraid.
 
Yes thats what I thought, all points towards a blockage. Perhaps the hole/leak it has is actively taking in a lot of air as it cools down and so I’m fighting a losing battle.

Well thanks for the offer anyway, I’ve given in and booked it into an independent specialist next week. He advised they would fix the leak before anything else as it can mask issues when trying to diagnose.
 
Robin82 said:
Yes thats what I thought, all points towards a blockage. Perhaps the hole/leak it has is actively taking in a lot of air as it cools down and so I’m fighting a losing battle.

Well thanks for the offer anyway, I’ve given in and booked it into an independent specialist next week. He advised they would fix the leak before anything else as it can mask issues when trying to diagnose.
Click to expand...
Let me know if you need a rad
 
You don't mention if you have checked the water pump is okay?

Eliminate possible head gasket failure by doing a sniff test.
 
Rockhopper said:
You don't mention if you have checked the water pump is okay?

Eliminate possible head gasket failure by doing a sniff test.
Click to expand...

As the pump isnt electric and the coolant seems to be at least moving through parts of the system, I’m not so sure it’s the pump.

I’m massively hyper paranoid about head gaskets going as It happened twice to a Z3 I owned some years back. No tell tale signs thankfully!

Thanks for your suggestions
 
enuff_zed said:
Robin82 said:
Yes thats what I thought, all points towards a blockage. Perhaps the hole/leak it has is actively taking in a lot of air as it cools down and so I’m fighting a losing battle.

Well thanks for the offer anyway, I’ve given in and booked it into an independent specialist next week. He advised they would fix the leak before anything else as it can mask issues when trying to diagnose.
Click to expand...
Let me know if you need a rad
Click to expand...

An update: took it to this Indy specialist, coolant flange is leaking, the one at the front of the block that feeds the hose to the expansion tank. So I’ve been quoted £270 for part and installation. Then they’ll refill, remove airlocks and pressure test for 100 miles.

I did know about this leak so I suppose I could’ve attempted fixing the hose. Seemed a little tricky to get at though as it goes right between the block next to the oil gasket.

So we shall see…
 
UPDATE: Replaced leaking coolant flange that feeds the expansion tank, ran a pressure test and diagnosed as requiring new water pump and stat.

Cost: £270 - wanted £580 to install new pump and stat so I pulled it out as I’m pretty sure I can get them installed cheaper than that…
 
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