Please help me - westerbeke 20b Impeller

[wantacruise]

I recently replaced the impeller in my westerbeke 20b after overheating it seems to be ejecting water okay but it continues to overheat.
I removed an old water heater and just connected the hoses in a loop coming from the engine should I have bled air out of the system ?

[dougweibel]

I don't know the westerbeke 20b but from your description of the work you did you may be misunderstanding how your cooling system works. Generally for small marine diesels you have raw water coming in a thru-hull, being pumped through the heat exchanger and exiting with your exhaust. You also have a fresh-water cooling loop with coolant circulated in the block and then pumped through the heat exchanger and water heater. The impeller is in the raw water pump. The fresh water pump is usually a gear pump you don't need to service. There is no reason to touch your fresh-water cooling loop when changing the impeller in your raw water pump.

There are several reasons you could still be overheating. You could have created an air bubble in your fresh-water loop. If your old impeller had fins broken off when you removed it they may be lodged in the heat exchanger blocking flow. Check the belt that drives the fresh water pump.

Others will probably have other suggestions.

[DougR]

It’s possible that you need to bleed an air lock out of the freshwater system, but more likely you have created a short circuit round your heat exchanger and you are just taking hot water from the engine, bypassing it around the heat exchanger and returning it to the engine without cooling anything. In other words there is not enough flowing thru the HE and too much bypassing the HE.

Instead of connecting the two hoses together you should remove the hoses and plug the outlet and return fittings.

[Sailmonkey]

Originally Posted by DougR

Instead of connecting the two hoses together you should remove the hoses and plug the outlet and return fittings.

This +1

[wantacruise]

Thanks for the feedback guys. I had suspected that those hoses that used to go to the water heater might be the issue plus I never did bleed the air out of the system so I think I have a double whammy going on there.
Any suggestions on how I can plug those outlets for those hoses if I take them off?
Also I was thinking of installing one of those on demand propane water heaters . . have any of you experimented with these and had any luck ?

[Cpt Mark]

Originally Posted by wantacruise

Thanks for the feedback guys. I had suspected that those hoses that used to go to the water heater might be the issue plus I never did bleed the air out of the system so I think I have a double whammy going on there.
Any suggestions on how I can plug those outlets for those hoses if I take them off?
Also I was thinking of installing one of those on demand propane water heaters . . have any of you experimented with these and had any luck ?

As you say, a double whammy. I'd look at both as the culprits.

re: on demand hot water heater. Had one on my last boat. Worked fabulously well. You will need to learn how to service it. On the Bosch I had there was a little screen filter you had to dig out and service regularly. Because of the design it was a major PITA. Bosch carried that design for their home units as well and I taught my landlord how to do it. If you go with one of these be VERY VERY careful on install. Do not mix up the water hoses installation as if you run it backwards like the previous owner of mine did it is a huge repair effort. Bosch was great to work with and once we identified the issues (I bought it used, supposedly never hooked up) I was able to repair it.