Gas Tank Issue

[MaidMarion]

Hi All,
I have a 2002 Marlin with F225's and I have recently been experiencing a fuel tank problem with my main tanks. Lately I can run all day on my AUX tanks, but when I switch to Main tanks, the engines start to cough and eventually stop( within 5 minutes). These are the corrective actions I have taken since this started late in the season last year.
1. Pumped out main tank completely( wanted to make sure the fuel wasn't contaminated, added new fuel with stabilizer ( unfortunately there is ethanol in the fuel, only type available in NY).
2. Replaced all fuel filters
3. Checked the bulbs that seem to be fine. Not flat when I checked after engines died.
4. blew out vents with compressed air to make sure they were not clogged.
5. replaced anti siphon valves.


Any help would be greatly appreciated!

 

[DennisG01]

To double check the vent system, you could run with the fill cap off. But since the bulb was not flat it's unlikely the issue... but of course that isn't a hard and fast rule.

Fuel lines can fail internally and create a check valve, of sorts. But that, again, would normally result in a flat bulb.

There could be something clogging the pickup tube in the tank (unless you pumped the tank out via the tube?). Remove the AS valve again and use some compressed air on the tank fitting. But... again, again... that would normally result in a flat bulb.

HOWEVER, since you've narrowed the issue down to the main tank, the issue has to be between the selector valve and the tank... which would typically result in a flat bulb... but remember, that isn't a hard and fast rule!

One last thing... it could be the selector valve, itself. Try swapping lines on the valve.

 

[glacierbaze]

Do both tanks run through the same filter?

 

[MaidMarion]

Thank you DennisG01 and Glacierbaze for your responses. There are 2 water separators, one per tank. I ran down today and got them both started using the Aux tank. Unfortunately the only real way to test is to take the boat out for a spin. I had the main tank on yesterday at the dock, both idle and 2500 RPM's for 20 -30 minutes and they ran fine, once I took the boat out for a trial run they died within 5-7 minutes.

 

[everwhom]

You could have an air leak somewhere between the fuel selector valve and the tank pickup (had this problem once). These can be hard to find, but you can try gently tightenting all the hose clamps or even better remove the clamps and inspect the hoses to make sure they aren't cracked.

 

[glacierbaze]

Do you have clear filters, or metal cans? Curious if you can see the fuel level in the main tank filter when the engines start to cough. You may pull enough fuel at idle, or even 2500rpm but no load, but not enough running on plane.
When it starts to cough, check the filter level, and as Dennis suggested, open the filler cap for the main tank. See if you hear it suck air in the fill, and if the engine clears up.

 

[Hookup1]

I have a 2002 Marlin with F225's and I have recently been experiencing a fuel tank problem with my main tanks. Lately I can run all day on my AUX tanks, but when I switch to Main tanks, the engines start to cough and eventually stop( within 5 minutes).

What happens next? How do you get them running again?

I would run one engine on aux and one on main until the engine quits. Drop the fuel filter can, dump out into a container and see if there is water and its completely full. Also pull cover off engine and do the same with the fuel filter on the engine.

If there is significant water then you have a water in fuel problem. Just because you drained the tank doesn't mean you got all the water out. It is always difficult to do so and I usually have to work the filter on the water to stir the tanks up and bring it up to the filters.

If the filters are low on fuel top them off with clean fuel snd re-test. If they are low when it happens again you have a problem pulling fuel from the tank. Using the fuel valves reverse which engine runs on aux and main tanks and re-test. There are separate fuel pickups in each tank. This will tell you which tank feed is a problem.

As said above I have seen hoses separate internally and the flap worked like a "joker" valve allowing flow in one direction and not the other.

The troubling part is that it sounds like both engines fail on the main tank. If it isn't water them I would have to believe its venting. Check the filter fuel levels, top off and try running with the fuel cap loose.

 

[seasick]

Are you sure you have one filter per tank or do you have one filter per motor?
Your problem does sound like fuel starvation. The fault may not show up at the dock because the fuel flow demand is lower than when running on the water.
Did you try Dennis's suggestion of running with the fuel fill cap(s) off?

 

[MaidMarion]

I tried the fuel cap open option when the engines starting quitting, no luck. Do you think fuel polishing might help? As mentioned I completely emptied the tank, checked the fuel filters, no water build up. I opened the small inspection hatches and checked the connections, they were tight.

 

[DennisG01]

To me, it doesn't sound like fuel quality is the issue (with the steps you have taken, anyways).

 

[Finest Kind]

Try this:
Swap the fuel lines that go to your motors coming out of the fuel selector valves.
So, now when the selector says "aux", its actually fuel from main, and when its says "main", its actually fuel from aux.

If the problem now occurs when using the "aux" position and now doesn't happen when using the "main" position, you know the fuel in the main tank is fine and its an issue with the fuel filters, lines, or the fuel selector valve itself.

If the problem, doesn't "move" and still occurs only when using fuel from the main, its definitely the gas itself.

 

[wspitler]

There are 4 filters in each engine system. (Water separator, engine paper filter, LP in line filter, and HP VST filter) I'd start by replacing them all since the LP and VST/HP filters can cause symptoms similar to what you are experiencing. The fact that they run OK on the Aux, your say tanks, (do you have two?) could be coincidence. Since they run OK at no load, I'd suspect VST. If those have not been changed, they will eventually need to be anyway. You may be focusing on the wrong area and it won't hurt to change all the filters. If you have already done all 4 for each engine. I may be off base. Good Luck!

 

[Uncle Joe]

Fuel lines...$2.50 per ft.....that is where I would be starting......sounds like it may be sucking wind through a cracked line.

 

[seasick]

Could be but a bad fuel hose but it would be between the tank and the selector valve
All those filters named are common to a specific engine and if they were bad, switching tanks shouldn't make a difference. The air leak is a possibility.
There is a very low possibility that the tank pickup is cracked and leaking. If the pickup tube is not removable, I am not sure how to test that part.

If this motor has an engine mounted clear bowl filter, immediately shutting down the motor when is experiences the rev issue , removing the cowling and looking at that filter bowl can tell you if gas flow was low. The bowl is normally about 2/3 or so full. If low, gas is not getting pumped into it. If full, it probably has an air leak in the filter bowl itself. If you have unscrewed that bowl at some point to say replace the element, it may not have seated correctly when reassembled. That can cause a small leak that doesn't leak gas but sucks air.

 

[Hookup1]

Take a close look at this photo. This is a 268Islander aux tank. On the starboard side you can see the fuel fill and vent line coming off of it. On the port side you can see the two fuel pickups.



The fuel pick line go to the tank switching valve, which go to the water separator can filter, which feeds the port or starboard engine. This fuel path is the same for both motors. There is nothing else from the fuel tank pickups out that is common to both motors.

If the motors work fine on the aux tank and not on the main tank and the problem is both motors, the problem has to be the tank.

Not to be a smart ass but how much fuel is in the main tank? When the motors stall how full are the fuel filters? Both the cans and the ones on the engines? You said you opened the tank fill cap. Is it possible you opened the wrong one?

How do you get the motors restarted on the aux tank after they shutdown on the main tank?

 

[seasick]

I was going to ask if he had gas in the main tank but decided not to..That would be obvious wouldn't it?

 

[Hookup1]

My guess is he is sucking some air with fuel on the main tank pickups (low fuel) when the boat is moving around. Eventually gets enough air in the fuel line to loose prime. The motors start acting up and eventually stall. Filters may not be that low.

Restart by pumping bulb to restore prime.

I doubt water in fuel because he didn’t say anything about draining filters or difficulty getting motors running again.

 

[seasick]

If it is low fuel levels, add 10 or 15 gallons of gas to BOTH tanks and see if the problem goes away. The reason I suggest adding to both tanks is that you may not be using the aux when you think you are using the main.
It's got to be something simple.

 

[Fishtales]

Could be the tank. 20 years on it. Maybe a pressure test and cleaning?

 

[seasick]

Could be the tank. 20 years on it. Maybe a pressure test and cleaning?

I don't think that will help much. If I read the symptoms correctly, either motor fails when it's source is set to MAIN but both motors work fine on AUX. IN addition all filters were changed but the problem remained the same. That tells me that it may not be bad gas since the problem would not clear up as soon as the aux tank was selected. The filters would be filled with junk. It's not a leak per se that a tank pressure test would find since a leak would result in either a gas leak that you would normally smell and wouldn't cause an engine to die. The pressure test won't fine a blockage since to do the test, the pickups have to be capped. I just would like to know if the OP is sure there is gas in the tank.