There are plenty of reasons why the diesel engine is the best power choice for boats over 35 feet, and principal among them is its sterling reliability and reknowned durability. Compared with even the newest electronic gasoline engines, diesels are signifitcantly less likely to suddenly stop running and significantly more likely to outlive their owners.
But diesels aren’t perfect. They do occasionally fail, and when it happens to be your engine that dies in the middle of some vast expanse of ocean, you’re not at all consoled by the fact that the odds were solidly against such an occurrence. But you can take comfort in the knowledge that because of the diesel’s comparative simplicity—it has no ignition system—finding the problem is a relatively simple process. All you need to remember is that if a diesel has two things—air and clean fuel—it’ll run.
Well, that’s not the only thing you need to remember. When troubleshooting a diesel—or anything else for that matter—there’s a kind of mechanic’s Hippocratic oath that should be your motto as well. It’s do the simplest thing first. Human nature compels us to think macro when we should think micro. “Yup, she threw a rod,” sounds so much more impressive than, “Hey, did someone hit the stop button?”
Thinking simple can save you a lot of work and money. So if your engine stops, you should stop, too. Stop and think: Is the ignition switch still on? The ignition breaker? Does the engine have fuel? (Yes, the gauge says it does, but is it accurate?) Did I open the other fuel valve when I switched fuel tanks a while back? In short, don’t even think about touching a tool until you have walked yourself through all of the basics. This can be very hard to do, especially if you’re wallowing in a gale far from home, but the reward for doing it just might be the welcome sound of the engine starting up right after you flipped the emergency shut off that someone inadvertently tripped.
Of course, thinking simple doesn’t always work, and when it doesn’t, it’s time to think macro. Of the two diesel necessities—clean fuel and air—fuel is by far the most likely culprit. Diesel fuel is, for reasons we won’t go into here, far more prone to contamination than gasoline, and diesel fuel-system components, having remarkably small tolerances, are far more sensitive than their gasoline counterparts.
The first place you should look to determine if your fuel is contaminated is your fuel-water separator. Most have a clear “sight bowl” on their bottom where both fuel and grit collect. All you need to do is shine a flashlight through the bowl from the back while you look at it from the front. (You say you don’t have that kind of access to your fuel-water separator? Then you better move it now before you have a problem.) Clean diesel fuel is red-amber and translucent. If neither is the case, you’ve got a problem because contamination has overwhelmed the fuel-water separator and stopped fuel flow to the engine. In other words, you’ve got a tank of dirty fuel. Your next move: Call for a tow, because even if you drain the bowl and change the separator’s particulate filter, chances are it’ll probably clog again.
This article originally appeared in the April 2007 issue of Power & Motoryacht magazine.