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Canal Boat - - This Month - TONY REPLIES:

Get­ting the wa­ter prop­erly hot; why some en­gines have an­odes; can you change types of an­tifreeze and BMC fuel pump leaks

QOur Volvo Penta 2002 raw wa­ter-cooled en­gine with wet ex­haust pro­vides hot wa­ter from a calori­fier fed by the en­gine. The pipe that takes wa­ter from the ther­mo­stat hous­ing to the ex­haust el­bow is cut into and the wa­ter is run (via the hose in­di­cated in the pic­ture) through the calori­fier heat­ing coil then to the ex­haust el­bow.

Wa­ter flows freely through the coil; the ther­mo­stat has been tested; but if I spend the day pot­ter­ing at 1500rpm (about 3mph), the hot tap gives tepid wa­ter only. If we run at 1700rpm (about 3.5 mph) so the en­gine is work­ing harder, the wa­ter is just warm enough for a fairly cool shower. What can I do to make it hot­ter? KEITH FROOM, via email

AOn a wet ex­haust sys­tem there must al­ways be suf­fi­cient wa­ter in­jected into the ex­haust to pre­vent the ex­haust hose burn­ing, ir­re­spec­tive of the po­si­tion of the en­gine ther­mo­stat. On di­rect raw wa­ter cooled en­gines this is usu­ally achieved by hav­ing a fancy ther­mo­stat ar­range­ment so that when the en­gine ther­mo­stat is closed the raw wa­ter by­passes the en­gine and is fed into the ex­haust. As the en­gine warms up, more wa­ter passes through the en­gine to cool it; how­ever there is al­ways far more cold wa­ter than hot be­ing di­rected to the ex­haust so the flow is never much more than tepid.

On some en­gines it is pos­si­ble to fit a dis­tance piece to the ther­mo­stat hous­ing mount­ing with a hot take-off from the en­gine side of the ther­mo­stat. On oth­ers it is pos­si­ble to mod­ify the pipework but as far as I can see from the man­ual a pipework mod is not pos­si­ble, and there is in­suf­fi­cient in­for­ma­tion to be sure a dis­tance piece (which would need ma­chin­ing and could be ex­pen­sive) and take-off will work.

Con­tact your lo­cal Volvo Penta dealer in case there is an al­ter­na­tive calori­fier take off point. You could also dis­cuss the cost of mod­i­fy­ing the en­gine to heat ex­changer cool­ing, which would pro­vide lots of re­ally hot wa­ter.

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