Sadly, the marine engine billows great clouds of blue smoke and you have to add a quart of oil every time you leave the boat dock. So what causes a marine engine to burn oil?
It could be the crankcase sump has been over-filled. But most likely you neglected oil changes and as a result gum and varnish locked the oil control ring in its piston groove. The stuck oil control rings unabled to flex are unable to scrape excess oil off the cylinder walls and dump it into the crankcase sump. The failed oil control rings let the piston pump so much oil into the combustion chamber that the spark plugs fouled and cold no longer fire a spark.
So when should you rebuild or replace an oil-burner? Or, can you get away with just adding oil for just a little while longer? The answer is the same for oil burning outboard motors, oil burning stern drives and oil burning inboards, gas or diesel.
That answer depends on how much oil the motor is burning. Consider the fact that a rebuilt marine engine will cost thousands of dollars. A new marine engine will cost even more. So as long as the engine starts and accelerates strongly and you don't mind the blue cloud of smoke following you like a flock of seagulls, you can get by. Here are two tips to keep an oil burning marine engine running in spite of it all.
Keep the crankcase oil sump full and the engine will burn less oil. That's because a low oil level means a lower volume of oil, so the oil works harder and hotter and the lubricant burns off. It's a lot like a mini oil refinery.
Even though you continually add oil, keep changing the oil and filter every 50- to 100-engine hours in order to remove particulate matter and acid held in suspension in the dirty oil.
Ultimately the day will come when the beast is stubbornly hard to start, and once started, it stutters on acceleration and runs rough. Sometimes cleaning the spark plugs remedies the problem, if only for awhile, before rough running returns. Sometimes transitioning to a hotter range of spark plug burns off the fouling. But once again, only for awhile. Then it's time to get out the checkbook.
This state of affairs gives rise to the question: Should you overhaul the tired old engine or instead opt for a rebuilt marine engine replete with the latest engine management systems?