- Check the engine, or engines, throughout the rpm range while underway. Note the oil pressure and water temperature at each designated rpm checkpoint. We recommend starting at 900 rpm and moving up at 300-rpm intervals, as we do in our boat tests. Check these against the manufacturer's recommended specs. Also, check for leaks along all the valves and components in the engine room. If found, it's an indication of sloppy installation or assembly.
- Look in the owner's manual for the engine's recommended maximum rpm range and make sure the engine falls within this range during your test. If it doesn't, this could indicate that your boat is outfitted with the wrong prop. Too low? Overpropping the engine can do serious damage over time. Too high? Underpropping can cause carbon buildup and harm the bearings. Experts say it should be on the high end of the range during tests so it will operate within the range when fully loaded.
- Check the color of the exhaust smoke while underway. With new engines, heavy white smoke could be a sign of problems with compression. Thick black smoke can signal, among other things, a faulty turbocharger or fuel injector. Blue smoke might mean something's wrong with the turbocharger or that the oil pressure's too high. Check the gauges.
- One thing any diesel engine needs is air. Lots of it. Check to see that the engine room has adequate ventilation. While underway, check the engine room with a vacuum gauge. If you get a negative reading, the engine's not getting enough air and won't be able to perform at peak levels.