A reader's question about engines gets answered by one of PBO's friendly experts


I’m an elderly retired marine engineer, and am helping my friend who has starting problems with his Yanmar 2GM.

If the engine is left for less than 24 hours since the last run there’s no problem in starting it, but if left for much longer than that it takes about six or more attempts to start – which takes a lot out of the battery.

I checked for diesel leaks and found none, so I then suspected a fault in the lift pump. I replaced it with a new one but that made no difference. Eventually I found a small leak on the fuel filter housing (between lift pump and injection pump) so that too was replaced, but again didn’t solve the problem.

I’ve also made some other checks and observations:

  • It seems to me that fuel is not getting to the injection pump until the starter has been operated for some time – but operating the lift pump manually prior to starting doesn’t help.
  • Fuel level in the tank is above the lift pump, so the suction pipe must be under slight pressure.
  • I have ruled out problems with the injection pump, injectors and compression because the engine, once started, runs well with little or no exhaust smoke.
  • All fuel filters are clean.

I am now running out of ideas, and wonder if you might have come across this problem before?

Robert Mackay
St Andrews, Fife


The thought that it’s a fuel problem is logical and your process of elimination is sound. It is worth taking into consideration whether the problem suddenly occurred or developed over some period of time.

If using the lift pump manually before starting makes no difference, I’d suggest you explore this a little further. You could bleed the engine via the fuel filter bleed screw before the attempt to start from cold to check that there is indeed no air. An extension to this would be to crack the injector lines and bleed these as well. If there is fuel all the way to the injectors and the engine still doesn’t start within 10 to 15 seconds, then I think we can rule out air in the fuel line.

Next, I suggest you turn the engine over for the equivalent time that it normally takes to start, but with the decompressors in use. It’ll be easier for the batteries to crank and will ensure that fuel, if available, will be injected. Then try starting normally.

The fact that the engine runs normally once started is not a definite indication that the compression is OK.

The actual temperature of the cylinder head is important, and even after quite a few hours the head may be sufficiently warm to allow the engine to fire up.

The 2GM has a pre-combustion chamber under the fuel injector but no pre-heating, so having sufficient compression to achieve combustion is important. The compression can be checked by removing the injector and using a compression tester.

It’s worth noting that it is possible to bend the connecting rod(s) by having water in the combustion space, and bent rods will reduce the compression ratio of the engine. Yanmar uses con-rods that will bend so that no more serious damage occurs in the event of hydraulicing.

This can be checked by measuring the ‘top clearance’ between the piston at TDC (top dead centre) and the cylinder head.

Here’s how to do it:

  • Remove both the injector and the pre-combustion chamber.
  • Lower the piston.
  • Insert some 1.2mm diameter fuse wire into the space and then crush the wire by raising the piston to TDC by hand.
  • Lower the piston, remove the wire and measure the thickness of the crushed part. The top clearance should be 0.68-0.88mm.

The full procedure is given on page 2-21 in the Yanmar 1GM10 service manual, which is helpfully available online at www.yanmarmarine.co.uk

Finally, one last thought: how old is the fuel? Blended diesel fuel with a bio content ages quite rapidly and suffers from a lowered cetane number, which can cause starting problems from cold.

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  • GwasinGreece

    When the lift pump diaphragm on the 2GM lift pumps fails it has a habit of leaking fuel into the sump. This fuel oil mixture can then cause the engine to ‘run away’. Check oil, see if it has any signs of fuel, or is overly full. If so, change oil, change fuel pump and have a happy season.

  • Raimo Lehtovirta

    I have a Yanmar 2Gm20 engine that has stood for four years. It was made repair of valves in the cylinder head. Now, when the engine is started, it will work only maximum speed. Adjustment affect anything. Similarly, the mechanical stop on wire does not work at all. Can you help me

  • Yachticus

    the little Yanmar lift pumps can be problematic – quick way of finding if this is the case is install a temporary day tank higher than the engine so it gets a gravity feed – of clean fuel. by doing this two things happen – any restrictions in the supply are eliminated and importantly you can isolate issue to lift pum/ injector pump or alternatively – the fuel delivery side of the process
    Our little grey beast – from time to time has fuel supply issues – installing a day tank sorted that issue out

  • Magnus

    Hi Paul
    We have a Yanmar 1gm10 which is hard to start, specially when it is cold outside (below 10 degrees Celsius). It would be great to get some hints from your analysis and solution

    Thanks in advance


  • Magnus

    Hi Paul

    We have a Yanmar 1gm10 which is hard to start, even more when its cold outside (below 10 degrees Celsius). It would be great to get an email of your analysis and see if we could get some hints about solutions.

    Thanks in advance


  • John

    Hi Paul:

    I would be grateful if you could share with me what you learned. I suspect I have a leak in the fuel system, but I can’t find it. If I bleed at the injector pump for awhile though the engine starts without issue.

    Thank you,


  • Paul

    I have had a steep learning curve with this issue with my 1GM10. I think I have got there as no problems at all after 6 months. Prior to this, despite the engine having done very little from new I had enormous starting problems. If you are interested I will email my lengthy analysis and how we got over the problem, I am delighted with what I have now.

  • John

    Hi there: my Yanmar 2GM20F has the same issue as written about above. I was just wondering if the fellow let you know what the problem turned out to be.