Strange water hose failure JE V6 automatic

[Anders Dinsen]

EDIT: Root cause found!

I planned to take the Espace to Le Mans but we barely made it out of Copenhagen before a water hos burst. While I was wating for the tow car I found with my finger a fairly large crack in a hose under the throttle body. This engine has been shoe-horned into the car and there is very little space around it, and no access from behind, so while the problem was evident and could be felt with a finger once the engine had cooled down, I had no chance of fixing it right away. The Espace was therefore towed back home and I took the electric BMW instead (it has fairly short range so that involved a relatively high number of charging stops and was thus a test of the charging infrastructure - test passed!) leaving, due to the BMW's smaller size, two friends behind for this years Le Mans  

I finally managed to remove enough parts and to get the damaged hose out yesterday, and I think the failure is interesting (I have torn the hose to peices while working to remove it, there was just a 5-10 mm crack in the side.)

Look at the grooves that have developed inside it. It's like the rubber has been "eaten" or "etched". I wondered how a failure like this could develop? Googling it, it seems there's a thing called electro-chemical damage to rubber hoses: This involves a difference in electrical potential coupled with some kind of chemical decomposition of the rubber. This can explain the logitudal grooves in hose.

There's a small joiner fitted between the water-to-oil head-exchanger on top of the gearbox, and I wondered if this has somehow played part in this breakdown coupled with some residue or dirt in the cooling system.

The documentation in the vault is not complete on this as the diagram of the coling circuit does not include the heat exchanger, but I've added that to the diagram below so you can see where the hose fits. It's the line from the top of the automatic gearbox back to the thermostat housing on the side of the engine.

Removing more hoses so I can get the hose with the joiner out, I realize that the joiner is made of copper. Also, the other hose has been etched with groves inside, and started to buldge out.

I have a suspicion who fitted this joiner, I paid him lots of money, but I can't make a claim now... 

I've found a piece of oil-compatible heavy 16 mm hose which I will fit. Hopefully that will get the car back to its former running state!

/Anders