Engine runs 10 minutes then stops

[s/v Jedi]

If you suspect a blockage, simply take the tank feed hose off the primary filter and blow compressed air into it. You will hear bubbling in the tank when okay but often nothing followed by a big blob when the clog shoots out. A good vent will blow air out and a bad one will gurgle. It means there is a valley in the vent line where moisture accumulates. When the mud dabbers built a nest in there you better look out :-)

[donradcliffe]

Last week's delivery challenge was a Yanmar that had to be bled every 5 hours. We hooked up an electric pump upstream of the Racor and it ran for days on end. The outside of the Racor is wet with fuel, which tells me that's where the air leak is. Its the second leaky Racor I've come across.

[vadrian]

Originally Posted by eje

Yanmar 3GM30F
I replaced both fuel filters & bled the system. The engine will run well for about 10 min then stops. I have to refill the filter and bleed the line between the filter & HP fuel pump, then it will start and run again for about 10 min.
I don't see any fuel leaks. I assume I have an air leak but can't find it.
Any suggestions on where to look?

So, you're having to bleed the line between the engine-attached (secondary) filter and the injector pump? Or is there some other HP pump you're referring to? On our engine, it's:
Tank -> Primary (Racor) -> lift pump -> Secondary -> Injector pump.

It sounds like you have a vacuum leak that's pulling air into the system slowly. You could try pressurizing the supply side somehow (maybe compressed air fed in from the fuel line at the tank?) and then spray soapy water all along. I'd detach it from the injector pump for this test, and plug that end.

It could also be, as others have suggested, crud clogging the intake. You start the engine, crud collects on the suction tube, eventually the engine stalls, the crud falls away again, etc. If you've not recently (last 2 years) cleaned your fuel and tank, that's a solid place to start.


Adrian

[thegui]

Originally Posted by Greg4cocokai

Also, check that there’s not a plugged screen on the pick up inside the tank. I’ve been on two boats where that was an issue.

I had the same thing happen. A piece of dirt from the tank got sucked up the pickup tube, got caught in the screen and slowly swelled up closing off the fuel supply. The motor ran for about 10-15 minutes. When the engine stopped the piece of gunk dropped back down the tube letting the fuel return to normal.
I also agree polish your fuel and if necessary clean your tank.

[Diantre]

Originally Posted by eje

Yanmar 3GM30F
I replaced both fuel filters & bled the system. The engine will run well for about 10 min then stops. I have to refill the filter and bleed the line between the filter & HP fuel pump, then it will start and run again for about 10 min.
I don't see any fuel leaks. I assume I have an air leak but can't find it.
Any suggestions on where to look?

Old diesel

[David Mathis]

Here's a different approach: Try tying or wiring the fuel shutoff solenoid open. If the engine continues to run, the problem isn't the fuel system, it's the safety system or the alternator. Many engines have safety shutoffs for overheating and low oil pressure with a few having an additional shutoff sensor for high exhaust temperature. If your engine has these safety features, one of the sensors may be faulty. These, along with the fuel shut-off solenoid, are usually connected to the alternator so if the alternator has a voltage drop, the solenoid will close. Connect a voltmeter to the alternator (not the battery) then watch for a voltage drop about the time the engine would quit. It's an easy check to perform. If no voltage drop, an alternator issue has been eliminated. Now, one at a time, bypass the sensors to determine which one could be faulty. Most are easy to change.

[David Mathis]

Are you getting air into the Racor housing? If the top is removed and fuel is at the top, air is not entering the fuel system before the Racor. If the fuel level is below the housing outlet, the system has an air leak before the filter.

[iduff]

Originally Posted by eje

Yanmar 3GM30F
I replaced both fuel filters & bled the system. The engine will run well for about 10 min then stops. I have to refill the filter and bleed the line between the filter & HP fuel pump, then it will start and run again for about 10 min.
I don't see any fuel leaks. I assume I have an air leak but can't find it.
Any suggestions on where to look?

You've answered your own question in the third sentence. When you provide fuel by refilling a filter that should not require refilling, it runs, then stops. You've got a fuel starvation issue upstream of your fuel filter.

Suggest you look closely at the lines and filter housings, and not the filter elements. We had a similar issue, turns out there was 20 years of crud at the bottom of our Racor housing that no amount of changing filter elements was ever going to fix.

Check and clean the lines and filter housings, right from the actual fuel pickup inside the fuel tank, straight through to the engine side of the fuel filter. then new elements, and you can rest assured that the fuel path is clean.

If the issue persists then, start looking at flow resistance, like any of the very good suggestions in this thread. But first ensure a clean fuel flow, as you have already identified fuel starvation to be your issue.

[JimZeigler]

A longtime ago, I had a single cylinder Yanmar that would do the same thing. On that engine, the excess fuel return line from the injector went back to the fuel filter. Apparently some combustion gas was ending up in the line. The mechanic moved the return line to the tank and pugged where it was connected to the fuel filter hosing. Never had the issue again. Not sure, but guess that the return spring in the injector was weak or the injector housing was fouled, causing slow closing of the injector plunger and combustion gas leakage back through the injector. Check where the return line from your injector goes. If it is back to the fuel filter, you may need to clean or replace the injectors or re-route the return line.

[Wolf Pack 2]

Originally Posted by eje

Yanmar 3GM30F
I replaced both fuel filters & bled the system. The engine will run well for about 10 min then stops. I have to refill the filter and bleed the line between the filter & HP fuel pump, then it will start and run again for about 10 min.
I don't see any fuel leaks. I assume I have an air leak but can't find it.
Any suggestions on where to look?

I had the exact thing happen to one of my yanmars, replaced racor, fuel filter, fuel pump, cleaned the vent and nothing. A old diesel mechanic told me to take off the fuel cap and start it again. Thought what the hell is that going to do, but did it anyway and haven’t ever had a problem since. Whatever obstruction was there, the added ventilation fixed it.

[Russ]

Air leak guaranteed. Yes check your vent first, it's easy. After that, it gets a bit harder. I have been there with my Yanmar.
First, wrap a small piece of paper towel around EVERY fitting from tank to engine. Running the engine may do it and show damp diesel on a section where the fitting is loose. Gotta remember the diesel engine SUCKS diesel so the air gets sucked INTO the fitting and for that reason you might see nothing even thig there's a leak. IF no luck this way, don't give up. You need to get a small pump and PUMP diesel through the system preferably staring at the tank end of the hose. This WILL show a leak if it exists in the system between the tank and the engine. Yes, I did ALL this to find my leaks (2) even though I have all copper flare pipe fittings!
PM me if you need more help. It isn't likely to be anything else (except the vent, Yes I had a spider web clog one of my vents once, too, same scenario engine running stopping, etc.
Russ

[Primipile13]

All good advice so far. Copper washers can be damaged easily. I always had problems with the o ring on the engine fuel filter. Too difficult access on my boat so I took it off the engine to an easier access point in front of the engine bulk head. At least I could see the diesel seeping out

[svfinlandia]

Originally Posted by gonesail

also when you are tightening up fuel filters .. it helps to dab a bit of silicon grease on the gaskets.

All good suggestions so far.
I had a similar problem last year. It turned out to be the Racor filter body itself. I don’t know which model Racor you have, but mine is the one with the see-through bowl on the bottom. It has a check valve where the fuel enters in, and that valve was nearly completely clogged.
I took the filter completely apart and flushed it out with solvent and the problem went away.
I hope you find the problem. It can be a real bear. It took me about a week to figure it out.

Al, S/V Finlandia

[NormanMartin]

I had that problem once. Solved it by carefully wiping dry all fuel lines and then pressurizing the tank by blowing into the tank breather tube. Bingo. A leak under a hose clamp revealed itself. Replaced hose and clamps. No more trouble.
Good luck.

[botanybay]

Originally Posted by Bill O

All good suggestions so far. Do you have a vacuum gauge on your racor? These are helpful for troubleshooting and letting you know your filter is getting clogged before the motor shuts down. Added an automotive vac. gauge between the racor and pump that is mounted outside the engine room. This made it much easier to view the gauge (rather than looking in the engine bay) to detect any problems.

As suggested by Chris and Greg, would start at the tank checking to see if the vent is clogged or a clogged pick up tube. Usually blowing air into them clears them out if there is a simple blockage. If the blockage is in the pickup, probably need to polish/clean your fuel and tank (did you have a lot of sediment/water in your racor when you changed it?).
Only reason I added "probably" to the statement above because we had this similar issue w/a tank pickup that clogged often. It turned out that tank had a fine screen in the end of the pickup tube and would clog with the smallest amount of stuff. Took much time to determine this issue and was very frustrating!

Try opening the fuel tank fill and see if the problem goes away. If so, then the vent is plugged