Marine Air unit loses prime

[bikeboybob]

Some of the time when I go for a cruise, the Marine Air unit loses its prime. I can prime it with a hose connected to water at the dock. It tends to lose prime when cruising above 12 knots. Does anyone know what might be causing this.

[DanM]

It might be a issue with air seeping into the system when throttling up and going bow high taking the intake out of the water or at least introducing turbulent water/air into it. That could be caused by a change in weight placement (bodies, fuel, water etc.). It that is not the case it is not uncommon that a pumps impeller has blocked water flow or starts to wear down.

You can do a few things. Make sure the intake is always in the clear water flow, the strainer and hose are clear from slime and debris. If that doesn't fix it you can put a bleeder valve just before the pump intake. If when you bleed the line it fixes the problem you probably have a failing pump or pump impeller which will need to be replaced (easy project). You also could have a scale filled cooling line in the AC unit itself but this is less likely.

[Lyndon670]

Another trick is to add a longer hose from the thru hull to the strainer/pump. Put a bend in it above the pump but still below the waterline. That way the pump will always keep it's prime.