E66 740Li Coolant Leak - A real head scratcher

[voodoomelon]

Hey guys.
Have a coolant leak on my E66 740 and it's doing my head in. It's the essentially the same N62 block as the 745i, 750i, 645i, 650i, 550i etc.

I only drive about 10-15 miles a day and in the last 2 weeks i'm leaking coolant at a rate of about a half a litre a day.

Car doesn't leak whilst parked up or idling, only when on the move.
I've had the car in the air for hours at this stage on several occasions looking up into the engine bay and I see no leaks from the radiator end of the car, so all looks good there.
Also see no leaks from the expansion bottle, any hoses, auxiliary water pump, main water pump or thermostat. It's also not leaking from the center weep hole on the block thank god so it's not coming from the central coolant pipe. I've also examined the lower radiator hose temp sensor which can leak, but it looks good, dry too.

After a drive and looking under the car, the stabiliser bar and main frame brace (the center jack point under the engine) is consistently wet, but that's all.

The whole front of the engine has been painstakingly cleaned and dried and there's not a sign of a leak anywhere!

I had the car pressure tested (it was hot at the time) and for 20 minutes three of us stood there with it running idle and not a single leak.

At this stage i'm thinking of sticking a GoPro in there whilst driving to see what the hell is going on, is it possible it's weeping from the somewhere on the front of the block, down onto the stabiliser bar and evaporating any residue on the front of the block?



:sad:

[Super4]

Hey guys.
Have a coolant leak on my E66 740 and it's doing my head in. It's the essentially the same N62 block as the 745i, 750i, 645i, 650i, 550i etc.

I only drive about 10-15 miles a day and in the last 2 weeks i'm leaking coolant at a rate of about a half a litre a day.

Car doesn't leak whilst parked up or idling, only when on the move.
I've had the car in the air for hours at this stage on several occasions looking up into the engine bay and I see no leaks from the radiator end of the car, so all looks good there.
Also see no leaks from the expansion bottle, any hoses, auxiliary water pump, main water pump or thermostat. It's also not leaking from the center weep hole on the block thank god so it's not coming from the central coolant pipe. I've also examined the lower radiator hose temp sensor which can leak, but it looks good, dry too.

After a drive and looking under the car, the stabiliser bar and main frame brace (the center jack point under the engine) is consistently wet, but that's all.

The whole front of the engine has been painstakingly cleaned and dried and there's not a sign of a leak anywhere!

I had the car pressure tested (it was hot at the time) and for 20 minutes three of us stood there with it running idle and not a single leak.

At this stage i'm thinking of sticking a GoPro in there whilst driving to see what the hell is going on, is it possible it's weeping from the somewhere on the front of the block, down onto the stabiliser bar and evaporating any residue on the front of the block?



:sad:

A dye test might be the way to go in this case, you should be able to pick up a good leak detector dye kit in a decent motor factors or a good indy garage should have something like this available. Hope you get it sorted.

[voodoomelon]

Was thinking the same only today, any idea what they cost?

[voodoomelon]

Turns out it's leaking from the front weep hole on the block, central coolant pipe is shot. Great! :/