Is this serious? Or did I do something stupid?

[Ginja]

I had a very similar issue on my 2001 540 E39. I owned it for many years and all its life it would lose a little coolant which would only become evident when I used the A/C - i.e. once a year I'd need to add a tiny amount to remove the 'low coolant' warning after using the A/C (I tend to use that infrequently). So this went on for 4 years, no problems. Then it got a little worse one year, i.e. more than one top up. Then after a long trip the warning popped up while driving which was a new one so I stopped at a petrol station to find water pouring out of the bottom of the expansion tank. Where the pressure sensor sits in the bottom of the bottle had failed so it had been leaking out of the sensor over the years, then after a long drive in the hot summer had just failed completely. New tank was about £60, problem never returned

Not saying its the same, just check the pipes, tank etc and don't assume the worst

Mark

[Targarama]

These cars normally need a cooling system refresh around 100k miles - radiator, expansion tank, water pump, main hoses, thermostat and expansion cap. Have these been replaced in the car's past? If not I suggest getting the whole lot done. Read up about the 5 series straight six cooling system and you'll find lots of forums telling you this.

[DonkeyApple]

I would just add that you are extremely lucky not to have burnt yourself.

Either leave an engine to cool or use a rag over the cap to halt the progress of steam to your hands or face.

[Smanks]

Shadows said:

Easy to find out if headgasket's goosed by a milky residue in either the oil or coolant. First thing I look out for when buying a used car.

Mayo doesn't always mean the headgasket is buggered, it can also be a sign of frequent short journeys

[TurboBlue]

eltax91 said:

Also, lets imagine it is, what's the bill for a strip down, head skim and gasket set on a 6 cyl bmw? Is it time for more k seal and trade it in??

When the HG went on my E39 the bill was £1,300 (incl. VAT).

[Evoluzione]

Do a compression test hot and cold, this may show up any problems.
When they did the water pressure test they should have taken the spark plugs out and looked into the combustion chambers to see if any water was forced in.

[16v stretch]

I'm 99% sure it'll be the expansion tank. Not hard to do diy.

I had a Z4 3.0 which had a hairline crack along the moulded seal for the top and bottom of the expansion tank, was only loosing coolant under pressure, and was barely noticeable as it was basically steam.

[steveo3002]

id expect to see a whitish /green powdery mark if its lost 4 ltrs

[Dr Doofenshmirtz]

There should be two level marks on the header tank, a cold line and a hot line.
If you top it up to the hot line when the engine is cold, these excess water [when hot] may go down the overflow tube.

[MaximumJed]

Could be the plastic tank on the side of the radiator. Seems to be a constant BMW failing to mount it directly to the radiator, plastic goes very brittle and then starts to break.

We also went through a similar amount of coolant, recently got worse though it wasn't dropping coolant anywhere, no obvious signs of a leak either. Dealer diagnosed it over the course of a day and the whole rad was replaced. Had similar with an X5 previously, and an E34 before that.

[Smanks]

MaximumJed said:

Could be the plastic tank on the side of the radiator. Seems to be a constant BMW failing to mount it directly to the radiator, plastic goes very brittle and then starts to break.

We also went through a similar amount of coolant, recently got worse though it wasn't dropping coolant anywhere, no obvious signs of a leak either. Dealer diagnosed it over the course of a day and the whole rad was replaced. Had similar with an X5 previously, and an E34 before that.

Or possibly the thermostat/thermostat housing

[Shadows]

Smanks said:

Mayo doesn't always mean the headgasket is buggered, it can also be a sign of frequent short journeys

It ain't a result of short Journey's, I'd be getting my car checked out if it had any in my oil or coolant..

[rscott]

Shadows said:

Smanks said:

Mayo doesn't always mean the headgasket is buggered, it can also be a sign of frequent short journeys

It ain't a result of short Journey's, I'd be getting my car checked out if it had any in my oil or coolant..

Certain GM engines (eg 2.8 v6) have what's basically a nice long plastic tube between the block and the oil cap. This can lead to the appearance of mayo under the cap after short journeys even if there are no problems at all with the gasket. I was specifically warned about this by the Saab dealer who sold me my car.

[eltax91]

In the cars history. Last year, it had a new rad. Around 115k

[getawayturtle]

Shadows said:

Smanks said:

Mayo doesn't always mean the headgasket is buggered, it can also be a sign of frequent short journeys

It ain't a result of short Journey's, I'd be getting my car checked out if it had any in my oil or coolant..

Erm, it's certainly possible. Six cylinder BMW engines do this.

[Herman Toothrot]

Dog Star said:

You've undone the cap, reduced the pressure hence the boiling point of the coolant. That's normal.

Quite basic primary school stuff really.

[Shadows]

getawayturtle said:

Erm, it's certainly possible. Six cylinder BMW engines do this.

I'm not saying it's impossible, I'm saying it shouldn't happen.. My mates 335i had it, but with the list of problems as long as the surface of Jupiter it could of been anything.

I'm not talking about boil residue from coolant either, I'm talking milky lumps of white stuff in your oil and in your coolant. That means serious problems, not a bit of white stuff under a cap like the GM engines.. Good tid bit of info though .

Edited by Shadows on Wednesday 24th July 14:34

[Smanks]

Shadows said:

Smanks said:

Mayo doesn't always mean the headgasket is buggered, it can also be a sign of frequent short journeys

It ain't a result of short Journey's, I'd be getting my car checked out if it had any in my oil or coolant..

Yes, it can be a result of short journeys, and not necessarily mean the gasket is gone, that is a fact.

[Shadows]

Smanks said:

Yes, it can be a result of short journeys, and not necessarily mean the gasket is gone, that is a fact.

I have never seen white milky liquids in oil and coolant from short driving, white bits from residue's sure. Any links, technical guides / readup's?

[VinceFox]

METHS said:

Try replacing the coolant cap.


Seems silly, but they are designed to let out pressure over 15psi, sometimes they "wear out" and leak slowly.


Leave a sheet of cardboard under the car overnight. sometimes the system will only leak while cold (happened to me).

Edited by METHS on Tuesday 23 July 23:32

This was my first thought. Also, chck the bit of bonnet sound deadening panel above where the cap is, are there any tide marks?