Skip to main content

The Case of the Mysterious Self-Starting Diesel

Q: Is it possible for a diesel engine to start up all on its own?

An event occurred recently on the boat across from mine in our marina that I found very interesting and thought your readers might as well.

The owner received a call from the harbormaster that one of his engines was running. This was a surprise to the owner, as he had not been on the boat—nor had anyone else—for days. The owner went to his boat and, indeed, his port engine was running.

After shutting it off, he called me (as I am a broker and have the listing on the boat) to see if perhaps I had shown the boat, which I had not. He also called the mechanical service provider. No one from their shop had been on the boat either.

The owner’s mechanic, who services the boat, mentioned that he went aboard and found both oil heaters on and the ambient temperature over 90 degrees. These are Detroit 12V92Ts, so the oil heater is engaged prior to starting the engines, however, they were on continuously.

The mechanic’s conclusion was that with the oil heaters on, plus the high ambient temperature, the engine became hot enough to cause combustion and started up. I would have never thought that could happen. —Chris Roth, Bay St. Louis, Mississippi

Chris: Thanks for reaching out. Wow, that’s a new one for us. We ran this up the masthead to our technical editor, Nigel Calder. You might have heard of him. Here’s his take:

“This is a two-cycle diesel, which complicates things a little bit, but nevertheless, I cannot conceive of any way a high ambient temperature and oil heater could cause a diesel engine to self-start. The necessary cylinder temperatures are so high (the ignition temperature of No. 2 diesel is almost 500 degrees Fahrenheit; No. 1 diesel is above 400 degrees Fahrenheit). You would also need diesel in the cylinder, and the piston would need to be at just the right point in the cycle to even get the first power stroke, and then you need the fuel rack open to keep the engine running …

“I think someone is pulling someone’s leg. Whoever last ran the engine forgot to shut it down!”