4 Stroke Trolling = Engine Failure??!!?

[ironhill]

I heard from someone who indicated their Mercury 4 stroke (60 or 90 hp I think and out of warrantee period) had suffered major power head failure (broken connector rod).

Their tech told them that "Mercury advises against long-periods of low speed operation (trolling) as the unburned gas builds up and dilutes the oil to the point of total viscosity breakdown, which resulted in the damage."

I believe the individual was sincerely passing along the explanation he was given at the shop.

I am no expert but I don't think this holds any water what so ever and it was a BS explanation of cause.

Please educate me if this is a valid concern.

 

[darnice]

Re: 4 Stroke not Recommended for Trolling??!!?

Re: 4 Stroke not Recommended for Trolling??!!?

Bull crap, I troll with my 90 HP 4 stroke 2008 on a 17' Lund all the time. Had oil anaysis done after the first 100 hrs and ther was no fuel in the oil.
So I think there were other contributing factors to a con rod failure.
These engines are thermostatically controled so it does not matter if your trolling or crusing, the oil temp and engine temp is pretty much the same. So any gas that goes into the oil would fash off just the same.

 

[Silvertip]

Re: 4 Stroke not Recommended for Trolling??!!?

Re: 4 Stroke not Recommended for Trolling??!!?

Some four strokes from ALL manufacturers have had issues with "making oil" and some more than others. The description given by the service tech is correct -- but he should have indicated that it is not an ALWAYS situation and trolling is perfectly ok if the proper precautions are taken . 1) Check the oil before EVERY trip. Do this for two reasons. A four stroke engine can consume oil and it must be kept topped off. If the engine is "making oil" due to dillution by fuel, then the oil level would rise on the dipstick. This condition may or may not be due entirely to trolling. It can also be due to an engine that is over-propped, meaning it has a prop with too much pitch and it is lugging. If making oil is caused by long periods of trolling, then every half hour or so open it up to heat up the engine so it can purge the fuel through vaporization. When done trolling for the day, make a long high speed run to heat up the engine. To make this perfectly clear -- EVERY four stroke does NOT have the problem. But SOME owners of EVERY engine BRAND have experienced this problem. IGNORE the possibility and you MIGHT destroy the engine. The capitalized words are not swearing -- they are intended to get your attention.

 

[j_martin]

Re: 4 Stroke not Recommended for Trolling??!!?

Re: 4 Stroke not Recommended for Trolling??!!?

In other words, it isn't the trolling that kills the engine, it's the lack of attention to operation details, like checking the oil periodically.

If you pull the dipstick and it smells like you just uncorked a gas can, something's wrong. If you don't pull the dipstick or don't pay attention, you would never know.