525 EFI with sea strainers in a Cigarette Gladiator. The front engine stopped pumping water while running down the lake. The engine was shut down. Over the next 20 minutes the engine was started 4 times to see if it would pump water. The fourth time it started pumping and ran fine for 20 minutes to get home. Nothing blocking low water pickups. This has happened twice before. Once while running and once right off the trailer with a new impeller it wouldn't pump. Upon disassembly everything looks fine every time. It's like it loses prime. This is three times in 5 years. Any ideas?

Pulley slipping?

Most of the Cigarettes I have seen have fresh water flush connections in the engine compartment. Are you certain there are no air leaks in the hose cap end of this connection, or any other parts of the system? Are you getting any water in the bilge? Are the sea strainers original equipment? They need to be mounted as low as possible in the hull.

Pulley is not slipping. No water in bilge. I think they are OE sea strainers and they are mounted low. I need to check the flush caps. The caps have not been used to my knowledge, fresh water boat.

I think the plastic pump/impeller assembly is roughly $100 bucks or so. I'd put one on, even if it looks fine. I tend to at most run impellers no more than 2 years, period; no matter how many hours.

Also, see these threads on replacing the lube inside the pump. Perhaps this is an issue?
http://www.offshoreonly.com/forums/g...pump-lube.html
http://www.offshoreonly.com/forums/g...-sea-pump.html

I know the 496 pump is significantly different but I did run into a similar problem when I installed new impellers in a worn pump body. The new impeller was not worn into the grooves on the end plates of the pump and would not seal there. It had a very difficult time getting primed. I must say that once running it would not lose prime.

I like the Sydwayz theory of an air leak.