I recently bought a 1995 Hunter Legend 35.5 and on two occasions have experienced air in the fuel lines causing the engine to stall and not restart both times. I've done a lot of troubleshooting and research but before I settle on my final solution I'd like to get a few thoughts from this board.
Hunter built their boats around the fuel tank in the swim step platform making it notoriously difficult to inspect or remove. The original tank was removed prior to me buying the boat, and a new shallower tank was installed at an angle many years ago by a previous owner (more than 2 owners ago). (Current Tank Size - 18” x 7” height x 36” width = 4536 cubic inches = 20 gallons)
Original tank size dimensions ~23.4 gallons (Friend with same model called with dimensions 25” star/port x 18” fore/aft x 12” high = 5400 cubic inches)
This new tank was cantilevered to port so the deepest side was 6 inches below the starboard high side.
I had assumed this was done because it was such a shallow tank and they wanted to keep the pickup lines much deeper than 7 inches. I had also assumed this tank had been slid through the starboard hatch for installation, otherwise why install such a shallow tank vs the original?
While the fuel pickup line is on the port stern corner, unfortunately the vent line is on the port forward corner and the fill line is in the center port in between these two...
After bleeding the fuel lines, replacing fuel filters and checking for air leaks in the lines we've been lead to the diagnosis that the angle of the fuel tank was causing the issue. The previous owner warned of sputtering when running the engine on any heel or high seas and to "Keep it topped off all the time." Both times I believed the tank to be at 16-17 gallons full out of 20 gal capacity. By the way the fuel gauge didn't work bc the sending unit was bad and I couldn't remove this until I dropped it because it was in the center of the tank under the swim step.
However after dropping the tank off the straps hanging it at an angle and emptying the tank, it appears I only had 11-12 gallons in the tank. Both the fill pipe and vent line would nearly overflow when topping it off but apparently about 5 gallons (cubic space) of air were trapped in the high starboard side of the tank. We believe that in the situations where I was in 2-4 seas/chop and/or a moderate heel, air bubbles that couldn't escape the tank were sloshed around until caught in the fuel pickup line since they couldn't escape to the vent.
However, the tank cannot be slid out through the aft hatches and their appears to be new fiberglass at the rear hull joints meaning the old tank was removed and new tank was installed by cutting the fiberglass. I'm hoping to go cruising to the Bahamas in March/April and really don't want to cut the boat again to install a different tank. ($$) This tank is sound, although it would be preferred to have the vent line and the pickup lines on different sides.
I can see the pickup line using an extendable mirror but unfortunately cannot remove the pickup line fitting. The line appears clear with no screen at bottom and just an inch above the bottom of the tank.
Our plan is to keep the original tank with a slight tilt aft so the pickup line is deepest and the vent is highest, both on port side. Not sure how much of an angle maybe just 1". I've also bought a Nauta 14 gallon fuel bladder to install on the starboard side (the port swim step locker contains the propane locker/tank which is temporarily removed for access).
We have several options to use this bladder as the auxiliary tank to keep the primary hard tank topped off. Planning to add a 12v dc fuel pump with toggle switch into the return line with a Y valve or into the fill line of the primary. I'll have to install a separate fuel fill deck fitting for the bladder, probably on the starboard side. The Nauta also has a vent fitting.
We are thinking of installing a hand pump before the Racor fuel/water separator to ease with bleeding the fuel lines if future air issues occur. Current Racor is solid and under after berth and not easy to see or drain. Long-term I'd like to replace this with one on the engine and a clear bowl but that's another day....
Engine is a Yanmar Diesel 3GM. I recently replaced the fuel injectors (long story) and otherwise she runs/sounds great!
Any suggestions on whether I should add a second fuel pump to the engine?
Should I keep the primary tank flat or at an angle?
What's the best solution for tying in the bladder or making it the primary?
Appreciate all comments or suggestions. Serendipity Sailing
First Post
Hunter built their boats around the fuel tank in the swim step platform making it notoriously difficult to inspect or remove. The original tank was removed prior to me buying the boat, and a new shallower tank was installed at an angle many years ago by a previous owner (more than 2 owners ago). (Current Tank Size - 18” x 7” height x 36” width = 4536 cubic inches = 20 gallons)
Original tank size dimensions ~23.4 gallons (Friend with same model called with dimensions 25” star/port x 18” fore/aft x 12” high = 5400 cubic inches)
This new tank was cantilevered to port so the deepest side was 6 inches below the starboard high side.
I had assumed this was done because it was such a shallow tank and they wanted to keep the pickup lines much deeper than 7 inches. I had also assumed this tank had been slid through the starboard hatch for installation, otherwise why install such a shallow tank vs the original?
While the fuel pickup line is on the port stern corner, unfortunately the vent line is on the port forward corner and the fill line is in the center port in between these two...
After bleeding the fuel lines, replacing fuel filters and checking for air leaks in the lines we've been lead to the diagnosis that the angle of the fuel tank was causing the issue. The previous owner warned of sputtering when running the engine on any heel or high seas and to "Keep it topped off all the time." Both times I believed the tank to be at 16-17 gallons full out of 20 gal capacity. By the way the fuel gauge didn't work bc the sending unit was bad and I couldn't remove this until I dropped it because it was in the center of the tank under the swim step.
However after dropping the tank off the straps hanging it at an angle and emptying the tank, it appears I only had 11-12 gallons in the tank. Both the fill pipe and vent line would nearly overflow when topping it off but apparently about 5 gallons (cubic space) of air were trapped in the high starboard side of the tank. We believe that in the situations where I was in 2-4 seas/chop and/or a moderate heel, air bubbles that couldn't escape the tank were sloshed around until caught in the fuel pickup line since they couldn't escape to the vent.
However, the tank cannot be slid out through the aft hatches and their appears to be new fiberglass at the rear hull joints meaning the old tank was removed and new tank was installed by cutting the fiberglass. I'm hoping to go cruising to the Bahamas in March/April and really don't want to cut the boat again to install a different tank. ($$) This tank is sound, although it would be preferred to have the vent line and the pickup lines on different sides.
I can see the pickup line using an extendable mirror but unfortunately cannot remove the pickup line fitting. The line appears clear with no screen at bottom and just an inch above the bottom of the tank.
Our plan is to keep the original tank with a slight tilt aft so the pickup line is deepest and the vent is highest, both on port side. Not sure how much of an angle maybe just 1". I've also bought a Nauta 14 gallon fuel bladder to install on the starboard side (the port swim step locker contains the propane locker/tank which is temporarily removed for access).
We have several options to use this bladder as the auxiliary tank to keep the primary hard tank topped off. Planning to add a 12v dc fuel pump with toggle switch into the return line with a Y valve or into the fill line of the primary. I'll have to install a separate fuel fill deck fitting for the bladder, probably on the starboard side. The Nauta also has a vent fitting.
We are thinking of installing a hand pump before the Racor fuel/water separator to ease with bleeding the fuel lines if future air issues occur. Current Racor is solid and under after berth and not easy to see or drain. Long-term I'd like to replace this with one on the engine and a clear bowl but that's another day....
Engine is a Yanmar Diesel 3GM. I recently replaced the fuel injectors (long story) and otherwise she runs/sounds great!
Any suggestions on whether I should add a second fuel pump to the engine?
Should I keep the primary tank flat or at an angle?
What's the best solution for tying in the bladder or making it the primary?
Appreciate all comments or suggestions. Serendipity Sailing
First Post
