Air lock in diesel engine

This is basic but essential….

Couple of seasons ago, I had several instances of air lock problems with my Yanmar 2GM, resulting in the engine cutting out.  There is nothing quite like your engine cutting out to undermine the confidence of everyone on board! We try to do as much under sail as we can – picking up moorings and coming alongside when conditions suit – it is good practice for situations where you can not fire up the engine for whatever reason.
In every case of Mr Yanmar cutting out, the single cause was dirt in the fuel tank clogging the system. Every inboard engine should have a primary fuel filter located on the fuel inlet line from fuel tank to engine. The filter needs to be changed regularly – at least once a season and otherwise as required. When I changed the primary fuel filter in the situation described above, I noticed it was quite dirty. I also examined the secondary filter located on the engine block and found this less susceptible to dirt, possibly because the primary filter is effective. I gave the fuel tank a complete clean and spent a few bob on a good fuel funnel. The funnel I had prior to this had a coarse filter mesh and was pretty useless in removing contaminants. This one does the job properly.


Everything that goes into the fuel tank passess through this funnel at least once. Never had an airlock in the two seasons since. It is an eyeopener to see the amount of contaminants held on the filter. I have added a job to my winter mantenance list – drain down the fuel tank completely and give it a good clean out. Funnel stays in the stern locker and is available when fuel top up is required. And I try to carry a new fuel filter on board as a back-up.

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4 Responses to “Air lock in diesel engine”

  1. graeme Says:

    Nice site, as a fellow Offshore 8metre owner, Offchance berthed in Hartlepool, it’s good to see someone promoting this very underrated boat.

  2. Tom Martin Says:

    I had the same engine in my old boat. I also have the same funnel. Cleaning you diesel tank is a good idea. I had my engine quite on me in a severe storm while passing a very tricky straight…not a good night. I ended up sailing through under bare pole. I slept that night with a life jacket on.

    • Donn Says:

      Hi Tom
      Thanks for your comment.
      The good funnel is such a simple measure and yet so essential. The more I learn about boats the more importance I put on getting the basics right. That is down to how you approach things -not something fancy gadgets can provide. I really rate the Yanmar – extremely reliable.

  3. Cambridgeshire Locksmith Says:

    Cambridgeshire Locksmith…

    […]Air lock in diesel engine « Nighean Donn's Blog[…]…

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