Mercruiser fuel pump vapor locking--how to cure

[mbjeeper]

Out on the Ohio river today, 95 degrees ambient, ran about 2 hours then shut down for a while. Boat has a new lower water pump and the temp never approaches the red in the temp gauge. (How accurate is the gauge? Who knows) The boat wouldn't restart. Actually, thats not quite correct. It started and throttled up for a few seconds and then died. Apparently the fuel in the carb bowl didn't flash off, so that's good. But when the carb bowl was empty the boat wouldn't restart.
Fuel not pumping from fuel pump. Fuel filters in carb inlet and on fuel pump clean. Pulled the fuel pump suction line and it was dry as well. Pulled the tank cover up and checked suction filter in the tank and confirmed fuel level (3/4 full) Check valve working OK.
I'm thinking a fuel pump now. Suffered the indignity of being towed in by a Jet Ski.
When I got home I pulled the pump and disassembled it, figuring it had a bad diaphragm. Nope. Looked great.
I mounted in a vise and primed it with fuel and worked it by hand and it pumps great. So the fuel pump is OK.
Almost certainly a vapor lock condition. Apparently it boiled the fuel pump dry and it lost prime. So how can I cure it? Install an electric pump between the tank and the mech. pump wired to a switch to reprime the pump when this happens? Go to an electric pump and do away with the mech. pump? How many psi of inlet pressure does the carb like? (I like the idea of two pumps, though).
Don't see how I could insulate or shield the pump from the engine heat. And it was really warm under the engine lid.
If anyone else has solved this issue ( I did a search and I see it has been on here a lot) I'd appreciate knowing how you did it. (I was unable to get to the faqs area of the Mercury Marine website that was posted a while ago that dealt with vapor lock.)
I know, I know, it's a 470 and most folks don't like them but it's what I've got and I need to keep it running.
Thanks.
Greg
Moundsville, WV

 

[Silvertip]

Re: Mercruiser fuel pump vapor locking--how to cure

An on-the-water fix for vapor lock is quite simple and the tools are close at hand. It's water! Drape a water soaked towel over the pump to cool it off. If under-cover temps are really high, another trick is to prop the cover partially open and let the engine idle for a couple minutes before shutting it down. You might even add another blower that directs outside air at the pump. Yup -- it's a pain in the back side but sometimes one needs to do what one needs to do! Electric pumps also need to be wired through the oil pressure switch so the pump quits when the engine quits. Don't want to continue to pump fuel into an engine that has just stalled because of a fuel line rupture or other fuel related issue.

 

[Coors]

Re: Mercruiser fuel pump vapor locking--how to cure

Yep, I'm with Silvertip, from drag racing days.
Install another blower directed at the pump.
and redundency never hurts.

 

[Bob_VT]

Re: Mercruiser fuel pump vapor locking--how to cure

Make sure your manifolds are not cracked. If the cooling manifold/riser has a hairline crack you will be shutdown. Sometimes this crack will spread when the engine is running.

The fuel pump is a simple napa item and easy to replace. They go frequently too.

My money is on the fuel pump and the cooling system. Been there done that with a 470.