540 - Where's my water going

[2linesontheroad]

Hi, as the title suggests i think I have a coolant leak. Its not a significant leak, Im having to top the header tank about every 2 months. The header tank has been replaced by a previous owner.

I cant see an external leak, but havent looked too hard yet... I just hope is not leaking inward!

Does anyone have any starting points?

Thanks.

[john_p]

Compression test?

[Huff]

Weak seal on header tank cap? Loose hose clamp?
Water pump?

(if the h/gasket had gone, it'd use water much faster than that)

[Maruchino]

Header tank is quite common I believe.

On mine my Radiator had bowed at the bottom like a banana. It wasn't visible from underneath but once we got it out it was obviously that it was leaking from one end of the bow. Apparently this can happen due to the radiator cooling down too fast, probably a manufacturing fault.

Since replacing (touch wood), I haven't needed to top up, and that was back in 2008.

[williamp]

My header tank split at le mans last year. I replaced mine, refilled but the weater kept dissappearing and needed topping up throighout the joruney home.

Once I got back i read the internet and discovered how to bleed the system. Once done, the "leak" stopped. I would suggest bleeding the system again.

[skeeterm5]

Is it an e39 540? I had one of these and the top radiator inlet tube split away from the body of the radiator letting all the water out.

I wonder if you have this but with a smaller split? As the water would then be running down the hot radiator it might be evaporating away hence no trace.

The solution for me was a complete new radiator.

S

[madou]

2linesontheroad said:

Does anyone have any starting points?
Thanks.

E39 540i has a variable thermostat. Cause of slight water loss on mine was the non OEM radiator leaking slightly when the thermostat was on a hotter range, such as 100's km along the Autobahn at high speed. And I was happy to see it had a new radiator when I bought it Just had valley pan coolant leak fixed

"Cooling System
Water pumps and thermostats are common failure points, with occasional radiator issues. The electronically controlled thermostats are prone to failure and set the “Service Engine Soon” warning. They can short out internally and melt a section of the engine wiring harness on the V8 cars."

From this link which credits the original source. See also radiator failure and coolant problem

Edited by madou on Monday 20th April 19:56

[miniman]

How low does the level get? You say you have to top it up, but is it really empty? Or just lower than you expect? Most cars will find their own level and always empty out down to that point and then stop.

[eliot]

I've had slow loss which was a hairline crack in the radiator near the top hose.
Another place to look is in the valley - you need to remove the plastic engine cover and look into the valley underneath the inlet manifold towards the rear where the geabox joins - you will see a small drain hole in each side, Look for wetness or evidence of staining.

[madou]

eliot said:

Another place to look is in the valley - you need to remove the plastic engine cover and look into the valley underneath the inlet manifold towards the rear where the geabox joins - you will see a small drain hole in each side, Look for wetness or evidence of staining.

Yes, this is subtle, mine was only leaking a few hundred ml per month, but I really don't like random coolant warnings

E38 valley pan write up

[B'stard Child]

2linesontheroad said:

Hi, as the title suggests i think I have a coolant leak. Its not a significant leak, Im having to top the header tank about every 2 months. The header tank has been replaced by a previous owner.

I cant see an external leak, but havent looked too hard yet... I just hope is not leaking inward!

Does anyone have any starting points?

Thanks.

Back of the engine 3 hoses from engine to heater and pump assembly

Replace all three - notorious for splitting

I'd put a £20 note on one of them having a split/pinhole

Copied and pasted from my running report on my E38 740 on the seven series register

Starts

Well since October the coolant level has required constant but small amounts of coolant to keep it at the right level

today the car got a run after a lot of short trips - a run is always good to stretch it's legs and blow out any cobwebs......

First time I put my foot down coming home it was getting dark and it chucked a load of white smoke out behind the car - hmm how odd

So I gave it another foot full and same thing again

That's not good I thought - take it easy keep the engine revs low and cruise home - about a mile from home I gave it another blast and it did it again

Basically produced a fog/mist bank from the rear of the car - not a head gasket gone fog bank more water on a hot exhaust engine fog

So as I pulled on the drive I popped the bonnet and yep loads of steam.

I can't see where it's coming from apart from

- the top of the torque converter housing is covered in coolant

- the bulkhead is the same

Sitting with the engine running on the drive it's hard to tell where the leak is coming from, in fact the leak isn't at tickover so I'm guessing I have a pinhole or small split in one of the hoses at the back of the engine. Squeezing them doesn't seem to re-create the leak so it's obviously at higher revs when the water pump is working hardest and the system has a higher pressure.

Feeling arong the back of a V8 to try and work out what hose was causing the issue got me a wet/damp fingers/hand - so I reckoned that the block to the heater motor hose was probably the one at fault.

Manipulating the hose resulted in spurt of coolant (was warm too - ouch)

So that was it I couldn't see the problem but it was close to the jubilee clip end and the hose had a bit of slack in it so maybe if the problem was close enough I could trim the hose and stop the coolant loss till I got all the new hoses and replaced them all

Lost a bit of coolant removing the hose

breaking up on the inside probably as a result of engine movement



And that would be a nice nick



An inch removed from the hose - refitted it (it's a bit tight length wise but better than a leak) and a quick washdown of the bulk head and gearbox housing to get rid of excess coolant.

Topped up the coolant and I'l do that again tommorrow when it's stone cold but a quick zip down the bypass showed no sign of the excessive steam behind when giving it the beans - good

Ends