GM fresh water pump priming tip

[MikeP]

Maybe everybody but me knew this already but I discovered that the GM FW pump will self-prime the system if the water tank is full. Previously, when de-winterizing, I would just start filling the water tank with a hose and pressurize the system as it was filling. This required a bit of priming at the pump fitting before it would pull water from the tank.

However, if I fill the water tank(s) first and THEN turn on the pump, it will self prime with no trouble at all. I'm guessing, of course but the "lift" involved when the tank is full is probably not more than a foot or two and whatever it is, the pump can pull it with no trouble.

[Diver Down]

Mike, is your GM mounted higher than the top of your water tank(s)?

[REBrueckner]

On occasion when I'd run my water tank dry on long cruises, my plain old domestic water pump (not a GM) would not pick up prime soon enough...maybe not at all, I never ran it long enough to find out.

So I put an extra valve and a TEE in the pick up line and could open it and suck water up 2 ft or so from the tank, on the pump intake side, by mouth and close the valve...the water column would remain in place.....My water pump would take it from there in just a few seconds.

[q240z]

I find opening a tap to be the easiest way to get my fresh water pump primed, even without the tanks full.

[MikeP]

"Mike, is your GM mounted higher than the top of your water tank(s)?"

I can't say for sure - I have never checked with a water level or other device but just from eyeballing it today, I'd GUESS that the pump is pretty close to being at the same level as the top of the tank so with a full tank there would be very little lift involved, if any.

I had never paid any attention to this before. But my previous method - priming when the tanks were just starting to be filled, resulted in a fair bit of futzing around whereas now, when the tanks are full, I just turn on the pump and that's that!