I need some help here. I have twin 502 EFI's and wanted to go out today.
I left the marina at idle speed, idled out about 300 yards and all of sudden the water temp alarm went off on both motors at the same time. I shut them both down, lifted the engine hatch to let things cool and jumped in the water to check the outdrives and see if any of the pickup holes were covered and couldn't find anything. I eventually limped it back into the marina and had it put on the rack and hooked the muffs up to the motors. when I started the motor no water came out of the exhaust at all. Nothing. I was out yesterday and it ran fine.
I could see something going on with one engine but both at the same exact time.
I would appreciate any ideas. I'm no mechanic and I just bought this boat, used but from a dealer.
1998 Formula 312 FasTech.

Its most likely the rubber impeller in the raw water pump,thats the place to start .if it has broken up you must back flush to get any broken bits out . also check pump housing for scoring . hope this helps

You just bought it? Did you run it on a hose at the dealership? I wonder if a shut off was installed in the line to run it on a hose and not use muffs?

I wish it was that but we ran it at the shop on muffs. I actually took their muffs since I didn't have any.

You probably have cooling tubes on the lower port side of the motors. Try pulling the rear water hose and feel in there with your fingers for seaweed, and also if the impellors got smoked there will be bits and chunks of the impellor blades in there.

Was the boat sitting for some time before you bought it? I could be the water pickup at the transom.Follow the hose to it and loosen the bolt 11mm I think see if thats restricted.As some one stated does the boat have strainers?If so are all the valves in the correct position.

Are they merc water pumps or aftermarket?

Good question.... stay away from the Sierra branded seawater pump kits and only use the Merc pumps & impellers.

Had a problem with a buddy's boat a few years back. Installed new Sierra impellers & housings and no matter what we did, they would not pump. Came back and installed a set of mercs and had no problems at all.

Thanks for your help guys. It was the impellers. They both got smoked at the same time. I found a thread on here on how to change them and did it myself. Both motors run fine now. That was a pain in the butt though, I don't want to do that again.

trewett, I believe it's recommended that you change those every other year.