Heater Hoses - M25

I have a Universal M25 diesel in my 35-3. I just installed a new Iso-Therm water heater, and it's inlet/outlets for the heatexchanger are 1/2" instead of the 7/8" that was on my Raritan. Can I just replace the hoses and fittings, and reduce them to 1/2" - or will I be harming the engine and it's cooling needs?

Thanks,
//sse

Sean,

I don't think that the change should cause a problem. The heat exchanger is sized to cool the engine without a heater and unless they are plumbed in series the restriction in flow should not affect the coolant flow through the heat exchanger. Tried to check the plumbing diagram in the manual but could not tell (poor quality copy). Will be glad to check the boat if it will help. Let me know.

Ray

Sean,

I have an M40 in Mean Jean, when I removed my Raritan water heater this spring for servicing I remember that my lines were 1/2" dia. I.D. The closed loop cooling system does circulate thru the hot water tank. I haven't seen a problem with this setup.

When I plumbed in my new Atlantic hot water heater and Heatercraft cabin heater, both being in the the engine coolant circuit, all the fittings were 7/8 "standard". Perhaps your heater is sized for metric hose, which might be coincidently about 1/2 inch American...
Other than the hassle of putting in a pair of reducers somewhere, I doubt that the restriction is enough to cause a problem, but I am no engineer.
Another thing to consider: some Universals were plumbed by the factory to put the hose to the hot water heater coil into the circuit with the engine block, and some put it in the circuit that goes to the heat exchanger (directing hot water in that direction after the engine warms up enough to open the thermostat. I know of an E-33 ('83) with the the later setup, and my '88 boat has the former setup. Howcome?? Idono!!
When I was doing my "all new coolant hose" project a couple years ago, the Galley Store guy at Doc Freemans told me that boatbuilders tend to do it either way with no clear pattern.
FWIW, we have just returned from two nights afloat, and last night got down to the low 50's, and we were sure glad to warm up the diesel this morning and have some cabin heat within about 15 minutes!
Loren in Portland, OR
1988 Olson 34 #8, Universal M25XP diesel

Sean,

Perhaps you have thought of this, but here goes. Continue to use the larger hose and use a combination of fittings to connect it to the smaller heater fittings. That will minimize the total restriction to the coolant flow.

Ray