Yanmar Water Pump Problem

[Compass790]

Originally Posted by Homer Shannon

This brings me to my last question. I measured the depth of the pump in the boat relative to the water line. The pump is at least ten inches below the waterline. This means that, when the boat is in the water, the pump never needs to be primed. Can I assume that, when in the water, the pump is going to operate reliably? I don’t really have any need to run the motor on the land any further.

Yes I think you will be fine if the pump is 10" below the water line.
You have already proved that it pumps when primed. Just check its pumping the usual amount out the exhaust when you splash her.

Do you have a temperature alarm on your instrument panel? That would be helpful if you have any impeller problems.

[Homer Shannon]

I have an alarm light but no buzzer. I'll know more once the boat is in the water. This little motor needs a rediculously small amount of water to cool it. Even after running for eight hours, the exhaust water is only about 90 degrees. You can put your hand on the motor and it's hot, but not scalding. Now I just need to make sure that the small amount of cooling the motor requires does not suddenly stop!

[Wotname]

Originally Posted by Homer Shannon

I have an alarm light but no buzzer. I'll know more once the boat is in the water. This little motor needs a rediculously small amount of water to cool it. Even after running for eight hours, the exhaust water is only about 90 degrees. You can put your hand on the motor and it's hot, but not scalding. Now I just need to make sure that the small amount of cooling the motor requires does not suddenly stop!

You might like to confirm the temperature alarm switch actually works by removing it, heating it hot water and check the contacts operate at about 55 - 60 C and are low resistance (i.e say <10 ohms).

As they rarely (if ever) operate in normal service life, the contacts inside do fail with age.

The thing is, you must make sure the internal temperature of the cooling raw water remains below 60C (if operating in salt water). If your pump is delivering less than the ideal amount of water, the internal temperature could be creeping up and if the alarm switch is faulty, you won't be aware of it.

Your engine won't be happy if running above 60C in salt water.

[Compass790]

Better to get an audible alarm as well. You can get them for peanuts on Ebay I imagine.

I have found the Yanmar sound alarm useful when motorsailing to windward on port tack as if we heel too much the intake comes out. The builders put it out to the side too much IMO. However doesnt sound like that will be so much of a problem in your installation.
Forgot to say maybe it would be safer to re install the cover plate gasket now you have it flat & your pump is 10" below intake so doesnt need to lift the water column. You might risk squeezing the impeller too much causing early failure with no gasket.
I would try it with the gasket installed in the sea first & see if it pumps fine.
I freaked out a bit when you said exhaust water was 90o but quickly realised you were talking Fahrenheit rather than Celsius that I think in.

[Homer Shannon]

All good advice. I'll re-check the pump once I'm in the water. I'll also look into an audible alarm. I had the temperature switch fail less than a full season ago, so that part is new. I was freaking out when the light started coming on. The temperature was normal, but this was when the motor was using a lot of oil. There's nothing (was nothing!) on board that said what the lights do and I assumed it was oil pressure. Nah, just a bad temperature switch.

[Halifax Sailor]

re: audible alarms,I got mine from Catalina Direct, 2 tone, hooked one to temp, one to oil pressure. Works great don't have to worry about noticing the lights.

[Homer Shannon]

I found this ariticle this morning. It looks pretty promising for adapting to my system that has no audible alarm at all. S/V Johanna Rose: Repairing a Yanmar 3-Way Engine Buzzer Alarm (one buzzer alarm for temp, oil, alt)

[morribabes]

I've not tried this, and I'm not in a position to do so as I've sold the boat, but I'm intrigued at the possibilities of the 12 volt water pumps available on Ebay for less than the price of a new impeller. If you connected one of these through a thermostatic switch in the engine block you could achieve rapid warm up and no danger of flooding the engine through over cranking.

[Wotname]

Originally Posted by morribabes

I've not tried this, and I'm not in a position to do so as I've sold the boat, but I'm intrigued at the possibilities of the 12 volt water pumps available on Ebay for less than the price of a new impeller. If you connected one of these through a thermostatic switch in the engine block you could achieve rapid warm up and no danger of flooding the engine through over cranking.

You want raw cooling water to be flowing through the exhaust from the get go.