Un­der pres­sure

Canal Boat - - Back Cabin: - JAMES2016, CB TONY REPLIES…

QEver since a ser­vice, in­clud­ing a pres­sure check, the ex­pan­sion tank on my Ve­tus 417 en­gine has been leak­ing. The ex­pan­sion tank over­flowed so I got a new one, but af­ter about four hours’ use, the new tank started over­flow­ing. Any ideas?

via the


On the face of it, a ser­vice plus a cooling sys­tem pres­sure check would not cause this, so I think there is some­thing more go­ing on. I sus­pect ei­ther the coolant was changed so new an­tifreeze could be added, or the pres­sure check found a leak and blew coolant out of the en­gine. In ei­ther case, I sus­pect the cooling sys­tem was not prop­erly bled free of air so now air is trapped in it.

This is the most likely ex­pla­na­tion be­cause you make no men­tion of over­heat­ing. If it over­heats as the coolant is ejected, check the hoses in case a clamp was left on one of them.

Air ex­pands far more than wa­ter when heated so it blows coolant out of the pres­sure cap. Try ma­nip­u­lat­ing the large cooling pipes so any air trapped in bends can make its way to the en­gine or skin tanks and then try bleed­ing the skin tank, which usu­ally has bleed plugs/screws at the top.

Fi­nally, it could be a symptom of a failed head gas­ket or in­ter­nal en­gine cracks – but elim­i­nate all chances of it be­ing trapped air be­fore think­ing the worst.

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