Fuel Pumps

JAC RMNF

Member
Apr 12, 2020
44
Boat Info
87 Sea Ray 300 Weekender
88 Sea Ray 300 Weekender
55 Lone Star Cabin Cruiser
Engines
350 Mercruisers
What type of electric fuel pumps are everyone using? Have replaced manual pumps with Carter marine rotary pumps and have them mounted near fuel selection valves. They constantly get warm and vapor lock requiring me to cool them with water before I can get back under way. The boat is a 88 300 weekender with vortex 5.7s. I've replaced the carters with an aftermarket mercruiser pump like the ones run on an 1994 4.3 and 5.7 but they do not last, have burnt up two in less than two weeks and are now removing and returning,. Thanks to a lifetime warranty on the pumps. Anyone have any ideas or advise? This is driving me crazy. I had looked into the Holley Red Marine pumps, but they say they have to push and I cannot gravity feed them through an anti siphon valve
 
I use Holley Red Marine pumps and have so for 20 years. They usually last 5-7 years then start to fail. I have small pressure gauges on the fuel rail to the Holley carbs. The Red pumps create/maintain 6 psi of pressure and when they start to fail....the pressure drops.

I'm not sure I understand your anti-siphon comment. My pumps are located after the fuel tank selection manifold on the down leg of the fuel line going to each engine.
 
My tanks have anti siphon valves right were the fuel is drawn from the tank. I'm pretty sure all tanks have the same valve in the same location. Have you ever experienced any fuel issues due to bilge heat effecting the pumps? I assume you ran the vacume line from the pump to the carb?
 
I have a '94 300DA with twin 5.7 Carbs and mechanical pumps. Located in South Carolina (hot muggy summers). I have never had the fuel pumps vapor lock. I have had the carb bowls boil dry after a hard run if I shutdown quick. Then restart will require a bit extra cranking to refill the bowls. But even that I can avoid by letting them idle for a bit and keeping the blowers running a while after shutdown.

Did you replace the mechanical pumps with electric due to fuel bowl issues like above and long crank times?
Yes it can help that as the carb should refill quickly as soon as the key is on.
But if the issue was not just the bowls going dry you may have simply moved the problem from the mechanical pumps to the electric pumps.

So first you need to determine why you vapor lock so often/easy?
This could itself be shortening your pump life.

Let's take a quick look at gasoline fuel systems, how and why they are the way they are and pros/cons of different solutions. This will be worth while in understanding how to get to the root cause. I am a retired USCG Machinery Technician and ASE Master Truck and Auto technician. Back "in the day" when most trucks still had carburetors and all the gasoline boats did. I worked as well on many fuel injected autos and still do all my own engine work.

So at 90F gasoline has a vapor pressure of 7.5 PSI, so just sitting in the fuel line with no where to go it will be 7.5PSI. If it can find a place to get out it flashes to vapor. If the bowl level drops the float opens the bowl valve and the fuel in the secondary filter and lines will start to boil off. At 200F it has a vapor pressure of 50PSI. So in a hot engine room gasoline is really trying hard to flash to a vapor. Add to this is any pump pushes a liquid better than it pulls , if you put hot gasoline under even a slight vacuum trying to "pull" it to a pump it wants to flash off to vapor.

Auto makers got around this problem by going to in tank fuel pumps. This keeps the pumps cool and never pull but always are pushing the liquid. This is surprisingly safe due to the physics above. The gasoline vapors displace any air inside the tank, without oxygen the vapor is to rich to ignite even if the pump somehow shorted in the tank. There must be some reason this is not acceptable in boats but I can never find why, it would resolve many of these issues both carb and "Cool Fuel" injection issues. And this is the one area fuel injected is nice, quicker starts, better idle. The entire fuel system is sealed when the injectors close and fuel is contained at higher pressures. But then injection adds a whole new level of complexity and cost for little gain on a boat vs cars.

And finally gasoline is heavier than air so all these fumes settle in the bilges. Therefore ventilate, ventilate and ventilate some more.
You're working with both gasoline and electricity please be very careful.

So the end is heat is our enemy and we need to contain the fuel as best we can, without restricting flow.

My boat has the anti-siphon valve, to a Fram filter on top of the tank, lines down to the stringers, across to the mechanical pump up to the secondary filter, and carb. So most of this is mounted low in the coolest part of the engine room, the ventilation exhaust hoses are under the engine. I have no selector valves, that may help me.

So consider where your pumps are mounted. Can they be lower? Are they in a poorly ventilated location?
Check the vent hoses are they all attached properly to the blowers and vents? Can they be relocated for better airflow?

Any restrictions on the fuel suction side are going to make things much worse.
Start at the tank, remove the anti-siphon valve check it for wear and or any clogs, it should open with the slightest suction, if in doubt replace it.
If the AS valve is not sealing when closed gas in the feed line will vaporize and push back into the tank this will cause longer primes.
Check the primary fuel filter, it should be a simple pleated paper cartridge, it should NOT be a fine cloth bag or resin type. It should be no less than 10 micron rated. Avoid "racing/performance" filters rated at 5 micron, to restricting. It is just there to catch some water and keep large dirt out of the pump.
TEMPORARILY replace the anti-siphon valve with a standard hose fitting if you can. With relatively full tanks you should easily get a siphon started and good flow all the way to the pump inlet. If not find the restriction, old hoses collapse internally, the selector valve could be clogged.
When satisfied you have good flow RE-INSTALL the antisiphone valve.
Re connect your pump and try again.

Good luck, be patient...
 
My tanks have anti siphon valves right were the fuel is drawn from the tank. I'm pretty sure all tanks have the same valve in the same location. Have you ever experienced any fuel issues due to bilge heat effecting the pumps? I assume you ran the vacume line from the pump to the carb?

I thought someone had installed something different on your boat. The tank valves have no effect on the Red Marine Holley pumps. The vacuum line on the pump runs to a port I installed on the spark arrestor. That line is to vent the pump.

No problems with heat and the pumps. I have them set up with a ball valve and a crossover hose which will allow both engines to run off either pump if one fails (not on plane but a reasonable cruise speed). The crossover makes it simple to get home if one of the pumps goes bad. They are also wired into a Holley oil pressure switch which cuts power to a pump if oil pressure goes to zero on an engine.
 
John,
your 370 I assume has a little more engine space, My 300 I can barely get my arm between the engines.
Where did you mount the pumps? Where did SeaRay place the selector valves? Got any photos?

Jac,
Same questions really, got any photos of your setup?
 
I'll look but it might have to wait until I get to the boat this weekend.
 
Here you go:

upload_2020-9-17_15-51-18.png

upload_2020-9-17_15-52-8.png

upload_2020-9-17_15-52-37.png
 
My issue is not with the carburetor or heat sink issues because when I had mechanical fuel pumps there was never a issue with the fuel when I replaced the engines with vortex which does not have a space for a mechanical fuel pump I was forced to convert to electric. I know it's the electric fuel pump vapor locking because if I take a block of ice or a cold water and cool the pump down I'm ready to go again. I have my pumps mounted on the downward piece underneath the fuel selectors right next to the engine bay fire extinguisher. From the looks in your pictures your fuel pumps are mounted underneath the engines correct? And they're pulling fuel all the way from the tanks with no issue?
 
My engine bay stays at a high temperature because I have a generator running also and it keeps the engine bay at a hundred plus degrees
 
I thought someone had installed something different on your boat. The tank valves have no effect on the Red Marine Holley pumps. The vacuum line on the pump runs to a port I installed on the spark arrestor. That line is to vent the pump.

No problems with heat and the pumps. I have them set up with a ball valve and a crossover hose which will allow both engines to run off either pump if one fails (not on plane but a reasonable cruise speed). The crossover makes it simple to get home if one of the pumps goes bad. They are also wired into a Holley oil pressure switch which cuts power to a pump if oil pressure goes to zero on an engine.
Thanks
 
John,
your 370 I assume has a little more engine space, My 300 I can barely get my arm between the engines.
Where did you mount the pumps? Where did SeaRay place the selector valves? Got any photos?

Jac,
Same questions really, got any photos of your setup?
I'll try to get some pictures later on.
 
Photo 88 300 Weekender
 

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Photo 88 300 Weekender
They are usually mounted but since I was in the middle of swapping them out when sally showed up had to keep them hooked up so I could move
 
My plan is to get the Holly red pumps, remove that battery and mount the pumps as low as I can on that middle stringer. should be well enough away from the exhaust hose to remove any possible heat that can get to them
 
From the looks in your pictures your fuel pumps are mounted underneath the engines correct? And they're pulling fuel all the way from the tanks with no issue?

Yes.....no issue for 20 years. Since they replaced mechanical pumps I just kept them in the same general location which makes them easy to get to. I will also add it made changing the raw water pump impeller a lot easier since I used to have a raw water pump with the mechanical fuel pump attached. It is just a different story on your boat finding the right location.
 
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