Everything the boatbuilder needs to marinise or fit out boats & yachts.
51 Victoria Road, Portslade, Sussex BN41 1XY, UK
Blog Menu
Blog Menu

Recovering a Submerged Engine (de-dunking)

Posted: 4 January 2023

With dunked engines the main thing is prompt action. Every day you delay makes things more difficult.

We saved a pair of 8.3 litre Cummins engines that went under a few years ago and though it took a couple of days to recover the boat and start drying out, within another day we had them running again, since when they have given little consequential trouble.

I would take IMMEDIATE EMERGENCY action as follows even if boat has been submerged for a few days, as soon as possible after pulling out of the water, as follows:- Speed is important. Even if it has been out of the water for more than a few days, I would try to run it as it is as quickly as possible.

  1. With a good strong hose jet, wash all over the engine with fresh water. Take off starter motor, put it a bucket of hot water for half an hour and then an hour or so in a slow oven set at about 100 deg.C. Spray WD40 in through the starter aperture between flywheel and cylinder block towards the crankshaft rear seal, and between the flywheel and the gearbox towards the gearbox input seal and its splines going into drive plate.Then re-fit the started.
  3. Undo sump drain plug and drain out any water there, replacing the plug as soon as oil starts to come out.
  5. Pull out injectors. Spray a lot of WD40 into the injector holes.
  7. Remove the air filter or air duct connection to inlet manifold on a turbo engine. Disconnect all wires going to alternator.
  9. Connect up a temporary fuel supply to the engine if you think there is water in the fuel tank. Disconnect the batteries that have been under water and connect up a temporary one for starting.
  11. Disconnect any domestic batteries.
  13. If water could have been trapped in the inlet or exhaust manifolds, drain it off by loosening from the head. Turn the engine over by hand a few turns, and then "jump" the starter solenoid to crank the engine over and expel water from the cylinders. Squirt some more WD40 into each injector hole and crank a bit more.
  15. Re-fit the injectors.Make a temporary connection to injection pump solenoid if necessary and go for a start-up. As soon as it fires squirt lots of WD40 into the inlet manifold this will make white smoke from the exhaust. Don't worry about water feed to the engine as impellers are cheap to replace.
  17. Keep blipping the throttle till the exhaust outlet gets too hot to touch. At this point you have probably SAVED rebuilding the engine, so drain the oil, change the oil filter and Jabsco impeller, fill with fresh oil, connect the mains water hose to the water pump inlet, and run the engine for an hour or so with lots of throttle blipping, or even better, afloat and tied up securely having checked gearbox oil and working hard in gear. 
  19. You should now be fairly sure you have the basic engine sorted. If oil is still creamy then change it again.You can now get on to all the other repair work needed, not forgetting at least the following:-
    1. Auto electrician to rebuild alternator. 
    2. Spray lots of WD40 on whole external of engine, including Jabsco and circulating pump bearings, idler pulley bearings.
    3. Keep a careful eye on these bearings for the next year or so in case water has worked its way into their permanent lubricant.

So all the best!


Gallery Images

Click on an image for a larger view.
We're happy to help. Call +44 (01273) 410025

About Lancing Marine

DIY Engine Marinisation guide

Latest Special Offers

Blog Posts

Borg Warnder
Payments accepted including bank transfer: