Why has our cruiser’s ex­haust taken up va­p­ing?

Canal Boat - - Back Cabin: Experts - RO­MAIN GOORMAN,


Our Volvo diesel’s wet ex­haust sys­tem puts out a lot of white smoke (or wa­ter vapour), more as the en­gine load goes up, and I have a feel­ing the cool­ing wa­ter blown out is less than it used to be. Is this in­di­cat­ing a prob­lem?

via email


TONY REPLIES: My first thoughts are lack of raw wa­ter be­ing in­jected into the ex­haust, which agrees with your ob­ser­va­tions, and the white fumes are wa­ter vapour. When wet ex­haust en­gines suf­fer a lack of ex­haust wa­ter it also com­pro­mises the en­gine cool­ing, but you do not men­tion hot run­ning or over­heat­ing. As­sum­ing you keep your raw wa­ter in­let and weed strainer/mud box clear of de­bris, the raw wa­ter pump’s rub­ber im­peller has prob­a­bly failed.

It has a num­ber of flex­i­ble rub­ber wings which even­tu­ally fall off, of­ten pass­ing into the cool­ing pipes and jam­ming in a bend or el­bow, block­ing wa­ter flow. Also, some of th­ese pumps run with­out proper bearings so the shaft or body can wear re­duc­ing the ef­fi­ciency. The pump, pipes and hoses are the first things to check in­clud­ing mak­ing sure all the joints be­tween the raw wa­ter in­let and the pump it­self are ab­so­lutely air­tight.

If the pump is in good order you might have a par­tially blocked ex­haust, caus­ing back pres­sure in the raw wa­ter sys­tem to pre­vent the pump from mov­ing enough wa­ter. First make sure the ex­haust-raw wa­ter mix­ing el­bow is free of scale. Then care­fully in­spect the ex­haust hose in case it is suf­fer­ing in­ter­nal de­lam­i­na­tion, which can hang down in the ex­haust stream and be pushed fur­ther down as the ex­haust flow in­creases, block­ing the ex­haust and pro­duc­ing more back pres­sure (and of­ten an au­di­ble hiss).

Too much or too lit­tle?

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