Generator raw water pump losing its prime

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Re: Generator raw water pump losing its prime

Postby Ortolan » Mon Jun 27, 2016 7:25 am


As a footnote, I had wanted to upgrade my Northern Lights control panel to their more "deluxe" one, which includes gauges as I liked the idea of having a water temp gauge. Unfortunately the panel is quite large & over $500!

A tech at Northern Lights told me that since a water temp sender is factory installed AND the wire harness already contains the lead, all you really need is a standard $30 gauge. So for $30 & an hour of time, I now have a gauge above my old control panel to observe the water temp, which should help foresee most cooling failures, rather than solely relying on the auto shutdown.

If anyone would like the wiring details, let me know.
Twin Sisters
2006 MV34 - Hull #100

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Re: Generator raw water pump losing its prime

Postby Expatriate » Sun Nov 19, 2017 1:06 pm

My gen set was not losing prime on the seawater side, but it was overheating after about five minutes. Basically just enough time to warm up. Of course I checked oil and water before I started it the first time. It overheated and I replaced the raw water impeller. Then tried it a few times, no luck. The belt was loose so I tightened it and tried it a few times. No luck. I replaced the overtemp cutoff sensor and tried it a few times. No luck. I was all ready to replace the thermostat so I checked the coolant again. It was a quart low!

When I checked the coolant overflow tank, way in the back, it was completely full! Good grief, what a simple problem to solve I thought. It had to be the radiator cap, but it looked brand new. The gasket is nice and soft and the spring is still stiff. So any expansion overflow goes into the tank, but is not siphoned back to the engine after it is shut down. That got me thinking back to previous engines. I had never seen an engine with overflow down that low. It is not designed to siphon back. No way. Looks like it was put there merely to prevent pollution. I figure that all of my test runs of five minutes each may have pushed out some coolant, but not a quart. Maybe a cup in the worst case. So now I think it was a little low on coolant and I blew it. The impeller definitely needed replacement, and the belt was loose enough to turn the pulleys by hand. The radiator cap is allowing too much overflow. The sensor was probably fine, but now I have a spare. All these things conspired to confuse me!

In any case, I have purchased a new radiator cap and an after market overflow tank. I will mount the tank high up and forward. The old one will just have to stay put. I could not figure out how to get it out and it really won't matter anyway. The new tank has the hose connection at the bottom so it should drain easily back to the engine header tank. When I topped off the coolant, the gen set ran like a sewing machine for about a half hour while we celebrated with a beer.

Any one else seen this?

Tim Denney
MV 068 Expatriate

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