Mercedes OM636 Cutting Out

[DAVE FOX]

My engine seems to cut out after about an hour of crusing. If I try to start again, even with full revs it won't stay running.

This has been happening for a while now, and have drained diesel tank and cleaned and new fuel filters but no change.

Does anybody have an idea on what the problem could be?

Thanks in advance

[Scubaseas]

Fuel starvation. Put a vacuum gauge on the fuel line which will indicate a blockage. Or check the pickup tube in the tank itself. If there is an elbow at the tank that maybe clogged. The boat I have now drove the previous owner nuts with new filters, new fuel & cleanish tanks but no flow. Turned out to be the elbow at the tank pickup tube was full of rust/sand.

Make sure you have the hand pump plunger secured properly. You can check and see if you lift pump is supplying the injection pump. Disconnect the lift pump to engine fuel filter line and crank engine.

To rule out the fuel system between tank to engine run supply and return hoses to a separate diesel fuel source, like use a jerry jug to test out if your tank to engine line is clogged.

[DAVE FOX]

Thank you for your reply. I'll check all of those things. Its just strange that it only happens after about an hour and not all the time.

[Scubaseas]

Take a look at the power supply to the shut off solenoid if you have one and/or make sure the shut off mechanism is moving freely.

[Cheechako]

Check your fuel tank vents, they may be clogged by bug nests creating a vacuum as you run. Next time your engine stops, remove the fuel fill cap and see if there is a vacuum there as you pull it off.

[skipperpete]

I haven’t worked on one of these in many years BUT, the last time I did it was for the same problem. The first thing I noticed was that the manual pump attached to the plunger type lift pump was loose, (ie not screwed down into the run position) but even after re priming the lines and tightening the priming pump she was still getting air so I hooked up a gravity feed from a can in the cockpit as a temporary measure and later, at the marina, replaced the priming pumppump. The new pump had no lockdown function, a vast improvement on the original.
Other than that , look for suction leaks between that pump and the fuel tank, perhaps fit a short length of clear plastic tube in the suction line to dismiss or confirm a downstream air leak.

[Scubaseas]

Bosch used that pump for literally decades on all their diesel cars & trucks. It's a common problem. The top o-ring shrinks and then the plunger vibrates out. Change the top o-ring and put a dab of blue 242 Loctite on the threads. Some people will tape it, use a hose clamp (not too tight or it'll crack) or drill a hole and safety wire it to keep it from rotating loose.

[DAVE FOX]

No electric supply, but its moving freely. I researched that the forward postion is for overfuel when cold. This isnt an option on my dash, but i can manually push forward. When having the cutting out problem, even pressing forward wont stop it from cutting out

[DAVE FOX]

Originally Posted by Cheechako

Check your fuel tank vents, they may be clogged by bug nests creating a vacuum as you run. Next time your engine stops, remove the fuel fill cap and see if there is a vacuum there as you pull it off.

I didnt mention that there are x2 engines. Both OM636. They get fuel from same tank. So when engine 1 cuts out, I can still keep cruising with engine 2 with no problem so guess this rules the vacum out?

[DAVE FOX]

Originally Posted by skipperpete

I haven’t worked on one of these in many years BUT, the last time I did it was for the same problem. The first thing I noticed was that the manual pump attached to the plunger type lift pump was loose, (ie not screwed down into the run position) but even after re priming the lines and tightening the priming pump she was still getting air so I hooked up a gravity feed from a can in the cockpit as a temporary measure and later, at the marina, replaced the priming pumppump. The new pump had no lockdown function, a vast improvement on the original.
Other than that , look for suction leaks between that pump and the fuel tank, perhaps fit a short length of clear plastic tube in the suction line to dismiss or confirm a downstream air leak.

I always make sure its tight as I havent tightened in the past after changing fuel filters and was losing diesel from it.

I will definately be checking for suction leaks between tank and pump.

If this was the problem, do you think it would be more consistent rather than just happening after an hour?