Pull the transmission dipstick too. Most transmissions use ATF, although some use lube oil—having the right one is critical, so if you're not sure which it's supposed to be, do some additional research. If ATF, the fluid should drip freely off the end of the dipstick and have a reddish hue. Dark, sluggish transmission fluid with a pungent, burned smell may indicate that an expensive transmission re-build is right around the corner.
While you're there and the engine is still cold, check the condition of hoses, belts, and wiring. While not expensive, these do add up if there are a lot of defects to repair all at once, and they each can ruin a nice sail when they fail. Inspect the motor mounts for signs of delamination or breakage—a flashlight and dental mirror come in handy. Don't neglect to check the exhaust hoses and muffler for leaks, as well as connections to a hot water heater.
Start ‘er Up If you're satisfied at this point, ask the seller to fire the beast up. Stand directly over the exhaust outlet while he cranks the starter, with every sense on full alert. Almost all of the problems that a diesel engine can have show up in the cold start. Many owners “pre-lube” their engine, that is, they crank it over with the stop applied. This is usually a good practice because it pumps oil to the engine's bearings before the high stress of actually starting. But in this case, don't allow the owner to pre-lube since it can mask engine starting problems. If the engine won't start at this point, of course, your inspection has ended, at least temporarily. Hopefully, it will catch immediately. If it sputters, coughs, spits, or cranks for an inordinately long time before smoothing out, you may need to go to the next inspection stage.
After the engine has run a few minutes, observe the gauges. Cold start oil pressure in many engines at idle is quite low, so don't be alarmed if you see only 20 pounds or so. Note the idle level on the tachometer—if it is more than 800 rpm, it may have been turned up to mask idling problems. Excessive idle rpm may have also caused transmission problems. Rev the engine up several times into the 2,000-rpm range, checking that the throttle control is smooth, that the engine responds without hesitation, and that it doesn't buck when the throttle is suddenly backed off. Some engines “hunt,” or roam up and down in a narrow rpm range at idle with a minor syncopated rhythm especially if the engine is turbo-charged, but this is usually not serious, unless it is excessive.
With all this done, there is only one thing left to do out on the water. If the seller has the engine manual, locate the manufacturer's recommended maximum rpm, and, after the engine is fully warmed up, run it wide open (yes, wide open!) for three to four minutes. Be careful at first that the tach does not exceed the max rpm for any more than a few seconds—if it does, the boat has an undersized propellor. The rpm should be within 100 of the manufacturer's recommendation. If it doesn't come up to that, the prop is too large, either in diameter, or pitch, or both. Running the engine hard, watch the temperature gauge—if it rises, you may have cooling problems. Also watch the oil pressure gauge to make sure that pressure doesn't fluctuate, which may indicate problems with bearings or the oil pump.
Drop Testing If you suspect at this point that a problem exists, one simple method of double-checking is with a drop test. Have a friend or cohort stand at the tachometer with the warmed-up engine set to run between 800 and 1,000 rpm. Loosen the first fuel line connector to the injector to disable that cylinder, having your friend record the level to which the rpm falls for cylinder number 1. Repeat this in turn for each cylinder, one at a time. When all cylinders have been tested, look at the numbers recorded. They should all be the same, or very close—if one cylinder has significantly less rpm drop than the rest, it may have fuel injection, or compression problems.
Replacing the Diesel Engine by Sue Larry
Electric Motors and Sailing Vessels by Mark Matthews
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