The Boat Doctor

Engine problems solved!

December 12, 2006

Screen Test
I have twin fuel-injected 5.7L Crusader XLs. I change the fuel filters every year and this year I changed the plugs, caps, and rotors. The engines run fine during calm conditions, but in rough seas the rpm on the portside engine bounces from 3200 rpm to 1000 and then back up. It doesn’t fluctuate when at idle, and if I let it sit, it restarts with no problem. What’s the issue? Frank Tiernay (via e-mail)

More than likely it’s a clog in one of the three fuel filters that Crusader puts on each of its engines. The first one to check is located where the boat’s fuel system connects to the engine. Inside the small plastic housing is a screen that prevents debris from getting into the engine. As it clogs, it will restrict fuel supply as you reach higher rpm. Your boat starts and runs fine after it sits because the sediment has settled. Take apart the housing, clean out the screen, and replace it. You should be good to go.

Kick Back
I have a 2000 MerCruiser 5.7-L that starts up, runs for a minute and a half, then stalls. After I restart, the engine stalls again. The warmer it gets, the more the motor acts like water is being dumped into the distributor. Why can’t I get it going? Orrin Cahoone, Exeter, RI


Pull the spark plugs after the engine stalls. If they look rusty and have water on them, water is getting in. Check the exhaust elbows and gaskets for water. If the plugs are soaked with gas, there’s a leak in the fuel system and it’s dumping too much raw fuel into the cylinder. If this happens long enough, the engine will lock up. If the plugs look healthy, the issue is engine timing. It could be caused by water in the distributor cap or by tracking in the distributor, which means two cylinders are trying to fire simultaneously. Make sure there’s no carbon in the cap and that the wires are clean. If the wires are dirty, they could fire at the same time.

Avoid Alcohol
I have a carbureted 2004 MerCruiser 5.7L with 1,020 hours. It runs fine, but whenever I top 3000 rpm, the engine sputters. This happens only when the boat is moving. I replaced the fuel-water separator. There was no water layer at the bottom of the bowl. There were some deposits on the distributor contacts so I cleaned them. I replaced the spark plugs, which were a good color when I pulled them. Can you help? Neil Ardolino, Sayreville, NJ

The float coming off the seat in the carburetor is probably jamming. The fuel pressure should be 6 psi at the inlet at wide open throttle. Also check what kind of fuel you’re using. If it has alcohol in it, the content level is supposed to be 11 percent maximum. When the boat sits longer than a few weeks, the water in the alcohol will wreak havoc on your engine’s fuel system.


Passing Gas
I have a 2005 29′ boat with twin gasoline engines. There’s a strong odor coming from the gas vents. The boat has a 200-gallon tank with two vents. I notice the odor at the dock and when I’m anchored and there’s a light breeze blowing. Do you know the cause? Vincent Del Priore, Point Pleasant, NJ

It sounds as if you have a ruptured fuel line somewhere and the odor is coming out the vents. Check each fuel line on the boat and don’t forget the filler and vent fittings. If one of these is cracked, it’s easy to miss, but it will cause a leak. And don’t try to turn over the engines until you fix this problem.

Oil at Rest
I’m awaiting the delivery of a new boat with a 375-hp MerCruiser 496 MAG engine. I’ve read several articles about using synthetic Mobil 1 oil versus the oils for marine engines and still have no clear answer on which oil to use. Can you give me one? Bryan Tudor, Lavonia, GA


Mobil 1 works great while an engine is running but marinized oils have detergents and additives to protect cylinder walls and other internal parts from rust buildup when the engine is at rest.

Bad Read
I have a 2001 Stingray 190XL with a MerCruiser 4.3-liter EFI engine. Last year the oil pressure gauge needle went all the way to the right-without even starting the engine. I e-mailed Stingray and was told to disconnect the wire from the oil pressure sender and watch to see if the needle moved when the key was turned on. This would indicate a defective sender. The needle didn’t move so I bought a new sender from my dealer. This didn’t fix the problem. Is there any way to check to see if the gauge is bad without replacing it? Bob Woessner, Kimberling City, MO

An ohm resistance should be stamped on the back of the gauge. Use a multimeter to check the resistance. Connect the meter to the signal wire and the ground, and start the engine. If you don’t get the right reading, you’ve found the problem. There could be a grounding problem. Check the wire harness for chafes in the insulation.


Fill it to the Brim
Anyone can spill a little now and then. but when fuel overflows, it’s not only harmful to the environment, it’s against the law. With a new deck-mounted fuel fitting from Securefill, you can clean up your act. I installed one on a Mainship 30 and was pleased to see that it worked as advertised.

Installation was pretty straightforward and took about two hours. I mounted it close to the existing fuel fill. Then I moved over to the gas dock to see how well it would work. When filling, you have to run a supplied clear vinyl hose from a quick-disconnect fitting in the unit into the tank fill neck. We took on 75 gallons and as the tank filled, the fuel that would have spilled all over the deck showed up in the vinyl hose-the signal that we were almost full.

I was concerned about maintaining sufficient airflow to the tank to prevent a vacuum while underway because I had to cut the original vent hose and join it to the Securefill unit. But a second vent line goes from the unit to the existing through-hull vent fitting, thereby ensuring the tank’s equalized air pressure. Securefill is available in two sizes-one for normal gas/diesel filling and a larger one for those boats that use high-speed fueling systems.

Price: Standard unit, $139; high speed, $179; Contact:


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