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Old 09-08-2014, 05:15 PM   #18
Scraping Paint
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Originally Posted by Bermudas2 View Post
Not to mention a sheen of oil behind us as well.
The sheen on the water behind a Lehman after startup is not oil as many people tend to believe, it's unburned fuel. This is the nature of the beast with old generation engines like the Fords, and does not indicate there is a problem. The reason is that until the cylinders come up to temperature, some of the fuel injected into the cylinder is not burned, so it goes out with the exhaust and forms a sheen on the water behind the boat. This is more noticeable in the winter than in the summer because the engine(s) will be even colder and it will take longer for the cylinders to come up to temperature.

The sheen should go away once the cylinders get up into the proper temperature range and all the fuel being injected is being burned.

Oil in the cylinders, as from leakdown past the valve stem seals after the engines are shut off, goes out the exhaust as blue smoke, which is why the Fords smoke at startup. They should clean up pretty well within a few minutes after startup. If they continue to smoke (blue), then there is a problem that is allowing lube oil to get into one or more cylinders This is most commonly a worn valve stem or guide, or shot valve stem seals, or all of the above.

A good friend who was the head of the engineering department at Northern Lights/Lugger (formerly Alaska Diesel Electric) for decades until his retirement the other year, told us when we bought our boat back in 1998 that eliminating the unburned-fuel-when-cold problem (because of the pollution) was one of the hardest things the engine designers had to figure out how to do. A I said, it's the nature of the beast.
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