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Posted by on Aug 31, 2011 in Engines, Maintenance, US |

Hydro-Lock: Engine Won’t Start

After a big storm (like the recent Hurricane Irene), why won’t my engine turn over?

Question: What is going on with my boat’s engine? I decided to leave the boat on its mooring during the recent storm surge from Hurricane Irene. I doubled up the lines and put on extra chafe gear, and everything went without a hitch. After the storm I tried to start my engine and all I got was a loud “thud” as the starter tried, but could not crank the engine at all. What’s up, and is it storm related?

This diagram shows how water can get into an engine in storm surge.

This diagram shows how water can get into an engine in storm surge.

Answer: STOP! Consider yourself lucky that you have not destroyed your engine.

What has probably happened is what is known as a “hydro-lock.” This is caused when an engine ingests some sea water and it sits on the top of one or more pistons. When you go to start the engine, the piston spins up in the cylinder and meets this wall of water in a closed environment (the engine valves are closed at this point).

Since water will not compress, the piston gets stopped short in its travel. In some cases the end result of this is a bent connecting rod, or sometimes they just break and end up flying through the side of the engine block. If all yours did was make a loud thud, be happy, you can fix it.

First, remove the spark plugs and crank the engine over some more and literally let the pistons pump the water out through the spark plug holes. Crank it over until the water stops spraying out of the plug hole. Re-install the spark plugs and fire it up; then you’ll be all set.

If your engine is a diesel, remove the fuel injectors and crank the engine over until the spray stops. Re-install the injectors and you’ll be good to go.

The obvious question here is: how did this happen? The answer is the excessive “hobby horsing” of the boat as it bobbed up and down during the storm surge. On one or more of its down swings, it forced a slug of water into the exhaust outlet on the outside of the boat and the force was so great that the water got pushed right up and over the exhaust elbow riser. The water then entered the cylinder(s) via any open exhaust valves.

I’ve seen this happen several times over the years. An engine with a stronger starter motor will typically destroy either a piston, connecting rod or crankshaft when this happens.
Ed Sherman