The Diesel Engine Dilemma

Should diesel engines be operated differently when they get older?

With the publisher’s Leopard 45 ‘ti Profligate about to leave the yacht management program at BVI Yacht Charters in Tortola for her new home at Antigua’s Jolly Harbor, we’re getting different professional advice on how her diesel engines should be treated. Marine mechanics tell us that boat diesels frequently go bad or have major problems at about 4,000 hours — but only because they haven’t had sufficient use. Unlike gas engines, diesels not only need to be used hard, they need to be used often. Lack of hard use hasn’t been a problem with ‘ti Profligate’s Yanmar 56-hp diesels, which despite still looking almost brand new, have more than 10,000 hours on them. They continue to run great and hardly burn any oil.

Nonetheless, Antonio, the terrific head of maintenance at BVI Yacht Charters, told us that because the engines now have over 10,000 hours, we shouldn’t run them at over 2,000 rpm, about 500 rpm less than we’ve normally run them."Nonsense," says Joe, who has been a lifelong marine mechanic, and whose backyard dock will be ‘ti Profligate’s new home. "Not running them at higher rpms is what will prematurely damage them."

So who is right?

Joe’s point of view seems to represent conventional wisdom, but has been nonetheless contradicted by the experience of Steve Schmidt of the Santa Cruz 70 Hotel California too. Schmidt, who worked in Silicon Valley before taking off cruising many years ago, tells us that his 75-hp Yanmar has 17,000 hours on it, and has been used almost exclusively for charging the boat’s batteries. In other words, extreme engine abuse.

If you know your diesels, we’d love to get your opinion.