540i coolant leak mystery?

[lysander2k]

Hi all,

First of all an apology I hate signing up to forums only to dive straight in with a question but hopefully I will be able to repay this in the near future!

I have a 1998 540i which has developed a coolant leak. At the moment I am having to put about 1 ltr in each morning to turn off the 'check coolant level' warning.

I have scoured the forum for answers but am still stumped! I have been above and underneath the car with a lead lamp removed the undertray and engine cover and spent ages trying to track it down but no joy.

I can't see anything obviously leaking from above, the radiator looks fine as does the header tank have also looked in the 'valley pan' area but can't see any wetness there. Wherever it's coming from its dribbling down onto the edge of the sump in front of the gearbox then dripping on the floor.

To further confuse things it only seems to do this when cold/not running - when its up to temp/running it seems to mysteriously dissapear?

Thanks in advance for any advice!

James.

[Huff]

Checked the heater hoses? these dive off from the auxiliary pump/valve arrangement on LHS bulkhead down and through the firewall in that are you mention.

When I started losing coolant it actually turned out to be this auxiliary pump; a split had developed in the very thin plastic enclosure between the pump rotor and the magnetic 'cup' that transfers drive to it from the pump's motor.

[lysander2k]

Thanks for the reply

Will start there in the morning when I can see what i'm doing!

Many thanks.

[neiljohnson]

There is pipework right at the back of the heads pita to get to but it sounds like one of these is leaking

[dan101smith]

Might sound silly, but are you sure that the coolant level sensor isn't faulty?

[willis54321]

Hi,

I have a 535 which had exactly the same symtoms. Like you I couldn't locate it, just a coolant stain up the right bank (as you look at the engine standing in front) Then one day, with lots of noise and smoke the alternator went! The V8 e39s have water cooled ones. Is your alternator noisy in any way? I would put money on this...............

[groomi]

willis54321 said:

Hi,

I have a 535 which had exactly the same symtoms. Like you I couldn't locate it, just a coolant stain up the right bank (as you look at the engine standing in front) Then one day, with lots of noise and smoke the alternator went! The V8 e39s have water cooled ones. Is your alternator noisy in any way? I would put money on this...............

Interesting! My 535i is leaking slightly. I have to put about a quarter of a pint in when the warning light comes on, but interestingly if I leave it three or four days, it still doesn't need any more. No signs of a leak anywhere either.

Alternator eh? I think I've had to replace the alternator on just about every car i've ever owned.

[sparks_E39]

Replace the entire cooling system, almost EVERY E39 will suffer from this if something else doesn't kill it. You only have to overheat the engine once, then its off to the scrappy. £400 well spent.

[willis54321]

groomi said:

willis54321 said:

Hi,

I have a 535 which had exactly the same symtoms. Like you I couldn't locate it, just a coolant stain up the right bank (as you look at the engine standing in front) Then one day, with lots of noise and smoke the alternator went! The V8 e39s have water cooled ones. Is your alternator noisy in any way? I would put money on this...............

Interesting! My 535i is leaking slightly. I have to put about a quarter of a pint in when the warning light comes on, but interestingly if I leave it three or four days, it still doesn't need any more. No signs of a leak anywhere either.

Alternator eh? I think I've had to replace the alternator on just about every car i've ever owned.

you've got a treat when you see the cost then......

[eliot]

sparks_E39 said:

Replace the entire cooling system, almost EVERY E39 will suffer from this if something else doesn't kill it. You only have to overheat the engine once, then its off to the scrappy. £400 well spent.

yep.

Take a look round the nearside end of the radiator for little whites water splashes - mine had a cracked rad and only leaked when hot and at high rpm. Like an idiot I only replaced the radiator ignoring advise to replace pump and stat.
Then sometime later the pump went - still didn't replace the stat against wisdom.
Then a little time even later,yep - the stat went - but it had overheated a couple of times by then.
And of course it ballooned the radiator - which needed replacing AGAIN!

[Denis O]

E39 cooling system is made of chocolate and the weakest chocolate is the join between the expansion tank and the rad. It's also impossible to tell where the hole is because it open when hot, coolant evaporates immediately and when it's cold enough to touch it's all closed up again.

A new expansion tank should sort it.

[cinnamon_whirl]

I had the same on my 540, got worse and worse. It was one of the two short hoses on the back of the motor that go into the bulkhead for the heater matrix. Take the engine cover off and you can see them and get to them. When one finally let go completely the AA guy knew exactly where to go. There are about £10 each. Easy fix - first place to look.