Cooling System - Any 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)

 

[Chippie]

Hi and welcome to the forum

It wouldn’t be getting air locked from simply removing the cap and topping up, it would only happen if the system has been drained or somehow lost most of its water, as you have had new thermostat and pump I would think that’s not the problem, I think the water pump is electric so I could be an intermittent fault with the wiring, connections/control module not activating the pump and so causing it to overheat.
I’m no mechanic and not had any problems with mine, just my best guess, hope this helps

 

[Chris_D]

When you say ‘water’ I hope/presume you mean proper ‘engine coolant’?

If you have an overheating issue and your stat is letting the coolant run above 100*C then water will evaporate off.
I suspect you have undercooling however. Are you sure that mechanic replaced the stat? Did you see the old one when the job was finished?
New stats can also be faulty on installation without the garage bothering to test it properly.

Have you tried bleeding the system properly? Car on slight incline facing forward. Engine on, heater on full, bleed cap off/loosened until coolant starts bleeding?

Suggest you also invest in an obd reader, pref bluetooth and ‘Torque Pro’ app so that you could monitor coolant temp precisely and independently of the temp gauge. Shouldn’t go over 98-99 deg ideally.

 

[brillomaster]

im confused, is the problem that you are overheating, or is the problem that you are losing coolant? or is the problem that you're getting a light come on the dash?

if you overheat, your temperature gauge will go into the red, and you'll get a geyser of steam from the radiator when you open the bonnet most likely. however, that doesnt sound like thats happening.

equally, it doesnt sound like you're actually losing much coolant - if theres a leak, it'll soon become apparent as soon as the car gets up to temperature, as the pressure will leak out.

if you've had a reputable garage drive it round for a week and find no problem, id suggest there isnt one. sounds to me like there is a dodgy coolant level sensor, which sounds to be about the only thing that hasnt been replaced!

Also, does your radiator have a float (plastic stick, normally red or orange, that has a float on the end)? if it does, open the cap and check that the float moves freely. the level of the coolant should be such that the float floats to the top, and that is then the right level. Also adding half a cup of water every couple of thousand miles doesnt sound like a problem - the total amount of coolant is like, 7 litres?!?

 

[Rucky]

I have topped up with 20mm of coolant on the floating dipstick twice in 10000 miles with no leaks visible, no drips, steam or other evidence.
On a different vehicle I DID have a small crack in the resevoir. The crack caused lack of pressure in the system so the water boiled at a lower temp and escaped.
A sealed system with a pressure cap boils at a much higher temperature than the nominal 100c for pure water at ambient pressure.
When your motor is at operating temp is there any steam anywhere to indicate its not holding pressure?

 

[Gibbo18]

Thank you all for your assistance. I would have responded to each of you individually and answered questions that you'd respectively asked; however I can't work out how you do that.

 

[colb]

Just post the answers to the questions on here everyone will see the answers and be able to see what direction to take in relation to things that may be causing your issues.

 

[mr.tourette]

Thank you all for your assistance. I would have responded to each of you individually and answered questions that you'd respectively asked; however I can't work out how you do that.

look at the top right corner of the post you want to quote.. there is a box with a quotation mark " click on that it will open up a new dialogue box with the quote in it that you can then type into

 

[ph001]

I’m fairly sure your car has a mechanical water pump rather than electric so a problem there is unlikely (plus the fact that it’s already been changed).

A duff thermostat should never cause loss of coolant so that doesn’t add up either (if that’s what is really happening as your story is a little confusing).

The expansion tank is certainly a weak point on these cars so you were right to change that.

What you really need to do is to have the system pressure tested. Search for a garage that can specifically do this.

 

[Gibbo18]

Thanks all for your respective feedback; however one quick thing to add if I may. The car is very slow in getting up to the mid point on the temp gauge and even when it does the lower hose is lukewarm at best. Is there anything in that ?

 

[javis20]

Have they done a pressure test? If your loosing fluid a pressure test will find the problem. My son's e85 was loosing coolant, we found it to be a leaky bleeder screw on the bottom of the expansion tank. It would only spray out coolant when the engine was up to temperature. Wasn't even visible. The other number issue for you to check is a cracked expansion tank. Again, a pressure test will find these problems.

 

[Collectingbrass]

Do you know whether the new header tank was a BMW part or a pattern part from a motor factors / spares place? Some non OEM tanks are very poor.

 

[javis20]

I just looked back to the beginning of your thread. You really need a new mechanic. I can't believe he keeps throwing expensive parts at the car. First thing should have been a cooling system pressure test. A simple diagnostic test could have confirmed the temperature sensors and thermostat operation.