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Ask Professor Diesel

How to exercise an unused engine

Caring for engines after a not-too-long hiatus.

Are end-of-season oil changes really necessary?

Should we do end-of-season oil changes or can we stretch the old oil into the next season?

How do I care for my unused engine?

I plan on being away from my boat for two to three months and during that time, I plan on having someone periodically run my diesels dockside...

Does an increase in horsepower explain a rise in exhaust temperature?

  Question: I have a 1989 38-foot Bayliner with twin 175-hp Hino diesels that have been retrofitted with turbochargers, thus raising each engine to 210 horsepower. As I go from cruise to wide-open throttle (approximately 23 mph at 2800 rpm), turbo exhaust temperatures increase from 700F to 950F on the port engine and 850F on the starboard. When

Can switching motor oil viscosity harm my engine?

  Question: The boys at the Ko Olina harbor are having a heated discussion concerning motor oil. Since Costco hit town, we’ve all been able to buy Chevron 15W-40 Delo 400 heavy-duty motor oil at ridiculously low prices. But what about the older engines we’ve been using straight 40W Delo 400 and other single-viscosity products in for years? Can we

Using synthetic oils in older engines

  Question: I own a 1996 43-foot Hatteras with twin six-cylinder Detroit Diesel engines. I change the oil approximately every 100 hours of operation. At this point, I have 1,200 hours on each diesel and so far have only used non-synthetic oil. Is a synthetic or a blend of synthetic and regular oil contraindicated for this aged engine for any

Vintage Yanmars Running Hot

  Question: I have a 29 Phoenix with twin, 1984-vintage, 170-hp Yanmar diesels with 1,000 hours on them. While the boat seems to run fine, I have one issue. During operation, the temperature of each engine rises normally at first but then keeps on going, not to the point of setting off alarms, but close. Pegging the engines (i.e., throttling them

Idling diesel engines

Question: My mechanic friends tell me not to let my diesel engine idle for long. They say that it should either be under load or turned off. I hear a lot of diesel engines in trucks idling at truck stops for hours though. Is there a difference in the two types of diesel engines or are my mechanic friends mistaken

Trouble-shooting an overheating boat engine

Question: I have a 1990 Carver Yacht with two 375-hp Caterpillar 3208 diesels. The starboard engine works fine, but at 2000 rpm the port engine overheats. Once the temperature hits 200F, I slow down to prevent damage and everything returns to normal.

Seasonal Storage For Fuel Tanks

  Question: When I took your one-day Introductory Diesel Maintenance Course several years ago, I forgot to ask one question: What is the best way to lay up a fuel tank for seasonal storage? For years now, I’ve been topping off my tanks when fall lay-up comes around in order to reduce the air space above the fuel and thus minimize algae growth. Just

Aluminum in engine oil

  Question: I just did my first oil analysis on my Cummins 6BTA diesel, and the results seem somewhat disconcerting. According to the report, there was aluminum in the oil at 28 ppm (parts per million) and iron at 20 ppm. The oil that was tested had approximately 43 engine hours on it. And since I bought my boat some nine years ago, I have

Caterpillar 3208 low rpm

  Question: I have a 1989 Sea Ray with 375-hp Caterpillar 3208 diesels. Last year I overheated one of them and blew a head gasket. Overheating had been a problem for some time prior, incidentally. Anyway, I determined shortly thereafter that the gasket had blown into the cylinder although no cooling fluid had escaped. So I hired a diesel shop to

Onan genset spewing black smoke

Question: I have a 4-kW Marine Onan genset with 600 hours on it. If I let it run for a lengthy period it produces so much black smoke that a residue discolors the hull around the exhaust port. A year ago, I cleaned the heat exchanger and installed a new raw-water pump. There are no overheating issues. Do I have an injector or rack problem?—Charlie Carpenter, Morristown, New

Noisy Engines

Question: I have a pair of Detroit Diesel 6-71 TIBs in my 1990 Ocean 48 Super Sport. I love both the boat and the motors, but the Detroits have always been loud at the exhaust end of things. As I grow older, this noise is starting to bother me, particularly at times when I have to shout to be heard on the flying bridge at cruise speed. Muffler companies tell me that modern

Twin Engine Temperature Disparity

Question: I have a 1994 Mainship 31 with a pair of 315-hp Yanmar diesels with 2,000 hours on them. While running at full throttle (about 33 knots) for five minutes, the starboard engine temperature creeps up enough to set off an alarm. If I ease ‘er back to half-throttle, the temperature returns to normal after a couple of minutes. The starboard engine has always run a bit warmer

Algae On My Racor

Question: While performing routine maintenance on my Caterpillar C7, I was surprised to find a substance about the size of a quarter at the top of my Racor—it looked like algae. There was no water in the bowl, and the engine-mounted filter was found to be clean. My Cat runs fine now and I would like to keep it that way. I am getting a lot of suggestions from friends as to what

Professor Diesel

Q. I have a 2003 Sea Ray Sundancer 420 and am moving from the New York City area to Florida soon. Do I need to do anything different in Florida in terms of boat maintenance? I am especially concerned about the warmer waters down there and the algae growth in fuel tanks I've heard so many bad things about.   Dan Markow North Haledon, New Jersey A:

Getting your engine ready for launch in the spring

  Question: I’ve always wondered if there was anything special I should do when getting my boat ready for launch in the spring. My mechanic says no, just start her up, but I wonder. — M.C.K., Tidewater, VA Professor Diesel: The best advice I can give anyone is to start with the engine’s operator’s manual.