Thread: engine hours
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Old 06-28-2014, 01:21 PM   #22
Irish Rambler
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Country: FRANCE
Vessel Name: 'Snow Mouse.'
Vessel Model: BROOM FLYBRIDGE 42.
Join Date: Apr 2014
Posts: 1,173
Most of the engine's are run at a gentle 1500 or similar cruising speed. Whilst it may feel good to be 'kind' to the engine what in fact is happening is that because the engine doesn't reach it's correct operating temperature a tiny portion of fuel is unburnt and is put into the exhaust system and creates a black oily coating on the inside of the exhaust manifold and piping. When the engine is gently opened up to WOT (monitoring for any overheating) the engine gets up to full temperature and the unburnt fuel coating also begins to heat up and starts to smoke. As the engine runs hard this oily coating will be burnt off and show itself as blue smoke, when the exhaust system is clean the smoke will clear and the engine will run sweet.
Older two stroke engines were very susceptible to this with a significant drop in performance until they become so poor that action is required either in the form of a costly strip down or, fill the tank with a 50/50 mix of Parrafin and diesel, as Parrafin burns hotter this helps the cleaning, the engine is run up under load (just like your Lehman) and run hard until it runs clear.
What is very important during this exercise, as stated previously, is that the engine is allowed to cool down naturally by letting the engine tickover until the temperature drops to around 70' Celsius to relief thermal stressing.
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