BMW Z4 - Cooling System Issues - Help Gratefully Appreciated

[Gibbo18]

Hi All

I've never visited forums such as these before and know very little about the workings of cars; however I've been advised that this may be the best port of call in order to finally resolve an ongoing and thus far unresolved issue that has puzzled four repair garages. As such any advice will be gratefully received and very much appreciated. Time line in relation to the issue as follows;-

1) Bought a 2008 BMW Z4 2.0i with just 62K on the clock in July 2019
2) Drove like a dream to 64K miles then all of a sudden the yellow warning light indicated the radiator to be bone dry
3) Topped it up and got 5 miles before the same thing occurred. Ended up having the RAC (service for broken down cars) come out, who's mechanic advised a faulty radiator cap, which was replaced with a new one.
4) No issues until 67K miles, when the same thing happens again without warning. RAC come out again and tow the car home, as they can't find an issue with it, but
don't want to risk me having to call them out again the same day.
5) Local mobile mechanic business of good reputation look at it and suggest a new radiator and header tank. Duly replaced both
6) No issues until 69 K miles, when the same thing happens again. Same mechanics advise a new water pump and undertake a sniffer test which confirms that the
head gasket is fine
7) No issues until 70K when the same thing happens again. Go to a different garage who suggest a new thermostat as it will mean that everything within the cooling
system is new. They also question if I've been topping the rad up with water and to make sure I leave a breathing gap at the top (Like I say, I know nothing about
cars ). A further sniffer test kit is undertaken, which again shows no issues with the head gasket
8) No issues until 73K when the same thing happens again. Take it to a third garage who run various tests and say that they can't find anything wrong with it, so
suggest it must be a faulty thermostat given that one was recently fitted. They also run various processes to look for air locks.
9) Take it back to the previous garage who agree to fit a new thermostat as the previous one is under warranty; however they say that they don't believe for a
minute that there's anything wrong with the original.
10) No issues until 75K when the same thing happens again. This time I take it to a garage that is recommended personally by a friend, who undertake a lot of work
on BMW's and have a good reputation. The proprietor personally drives round in it for a week and undertakes a number of tests, before saying that the car runs
like an absolute dream and that they can't find anything wrong with it.
11) By this point I'm now absolutely loath to even take the radiator cap off to check the water; however at 78K after no issues I feel I need to check the level. Put
about half a cup of water in and leave a good gap at the top for it to breath. Drive 20 miles and the same thing happens again!
12) Am advised to go onto this forum and seek help

Everything points to me giving up and getting shot of it; however the car looks immaculate, drives beautifully and has done less than 80K miles in it. One thing that has however been picked up within the above, is that the lower hose often remains lukewarm at best and the temp rarely gets to half way unless the empty radiator warning light comes on. A few people have suggested that despite the tests mentioned in point 8) that air locking could be the issue, given that the occurance has sometimes happened after the rad cap has either been removed and replaced, or removed and a bit of water added prior to being replaced.

I'm at my absolute wits end with it, so any assistance or advice will be hugely appreciated. Thank you in advance guys.

Duncan (Gibbo18)

[MauiM3Mania]

Moved discussion to model specific sub-forum.

Good luck!

[Clearancediver]

Not familiar with 2.0 engine but the real question is whether or not you have a electric water pump or mechanical (belt driven) water pump.

1st... never too up with water. Use proper mixed radiator fluid.

If mechanical it’s likely air in the system as suggested. The system needs to be bled with the nose of the car elevated as much as possible (drive on ramps/steep driveway). Once bled/topped up to the proper level and warmed up as much as possible find the steepest hill around and take a drive up a few times. That will get any trapped air out. If you don’t have a hill a parkade with steep ramps is the next thing I would look for. Top up the radiator if necessary afterwards....

Looks like you are in the UK... trip to Scotland perhaps? Lots of hills there....smiling...would like to visit across the pond and visit my G’fathers birthplace.

Electric pump has its own bleeding procedure but I’d still find the steepest hill etc around and go up it a few times as well.

While this might sound crazy it actually gets trapped air out.

Also.... look for evidence of radiator fluid leaks at the hose connections and expansion tanks


Sent from my iPhone using Tapatalk

[B328iC]

If you are having to top off the tank you probably have a leak. Get some dye for the coolant and run it with that for awhile. This will make finding the leak easier. Once you find the leak you can have it repaired.

[PbFut]

This is a good one. From what I gather, no leak evidence but topping off is needed from time to time. Occasional overheat.
Do you always get hot air from the heater, or does it sometimes seem it is not heating as it should? That is a sign of air trapped in the system.
So where is air coming from? It is possible you are getting air in the system past a head gasket or worse a head crack. The pressure of the combustion is enough to force a small amount of air into the cooling system via a tiny leak. After shutdown, the pressure in the cooling system is enough to force a very small amount of coolant back into the combustion chamber. This would explain loss of water over time with not leak evidence, and overheat issues from a phantom or occasional air bubble where the system can sometimes clear the air in the overflow tank if not overwhelmed by too much air forced in. Hence occasional overheat. Its a long shot and big effort/expense to repair so I would peruse other ideas first. Best of luck. This is not a fun chase.
Added on edit: This just came to mind. You could send an oil sample to Blackstone and have them pay particular attention to see if your oil has coolant in it. It would not be a lot as most of the leaked coolant would be blown out the exhaust but if elevated, its a good indicator. Also look at the inside of your oil cap. If you have a milky residue, that can also be a sign. This trick is not 100%. Condensate can show in this mannerl from time to time. I get it on my LS motor and its always a scary sight that self clears but it is just another clue to look for.

[Kram71]

When I did my thermostat and water pump on my Z3M I had similar issues. I had to bleed the air out of it twice to get it perfect.

[Gibbo18]

Thank you so much for taking the time to assist, it is very much appreciated.

Just out of interest is there a clue perhaps in the fact that the lower hose pipe rarely gets to lukewarm and the temperature needle rarely gets to half way and drops off a bit once it does?

- - - Updated - - -

Thank you so much for taking the time to assist, it is very much appreciated.

Just out of interest is there a clue perhaps in the fact that the lower hose pipe rarely gets to lukewarm and the temperature needle rarely gets to half way and drops off a bit once it does?

- - - Updated - - -

Many thanks for this; however can you advise how I access it. Like I say, I'm all very new to this.

[Kram71]

Thank you so much for taking the time to assist, it is very much appreciated.

Just out of interest is there a clue perhaps in the fact that the lower hose pipe rarely gets to lukewarm and the temperature needle rarely gets to half way and drops off a bit once it does?

- - - Updated - - -

Thank you so much for taking the time to assist, it is very much appreciated.

Just out of interest is there a clue perhaps in the fact that the lower hose pipe rarely gets to lukewarm and the temperature needle rarely gets to half way and drops off a bit once it does?

- - - Updated - - -

Many thanks for this; however can you advise how I access it. Like I say, I'm all very new to this.

With my Z3M my temp needle would move too high while my lower hose was not getting hot. I parked it in my garage and bled the air out. It improved greatly so I bled the air out again and that made it perfect. This was all after I replaced my waterpump, thermostat, housing and coolant.

If you bleed air out of the Z4 like you do the Z3 then you may want to try it.

[BimmerBreaker]

The lower hose is the radiator outlet - it is always supposed to be colder than the upper hose which is the inlet.

I would start by taking your car to a competent mechanic. It needs to be pressure test and bled

[Caver69]

Ever resolve this? My 2008 3.0i developed similar issue around 86k. Filled and bled, everything fine then suddenly a flash over temp that cleared. Next time out low reservoir light. Fill and bled, repeat. Another week and another flash overheat. Took it to my independent BMW mechanic, pressure test fine no issues. He did get a code for alternator and thermostat. Diagnosed a bad communication cable (seems the two share same cable) fixed, no further issues in the last three months.