Boat Maintenance Tips March '12

Outboard motor engineering and design have come a long way and the topic of four stroke versus two stroke outboards gets aired often. Opinions on performance and cost of operation range all over the map. Two stroke price tags are easier on the budget but four strokes cost less to operate - or so we're told. Let's see if we can unravel the puzzle.

Start with fuel consumption. Marine outboard manufacturers base fuel consumption on gallons-per-hour (gph), not the miles-per-gallon (mpg) formula we are more accustomed to seeing. While the gph rating may be useful for the manufacturers, I prefer to stick to the good old mpg rating because it is easier to relate to.

Here's an illustration…

A four stroke of 150 to 250 HP will usually be most efficient at around 4200 rpm with an average mpg rate of 3.5 to 4.0 - provided the boat is propped correctly, the trim is adjusted, and load (passengers and ALL gear aboard plus fuel load) does not exceed the capacity recommendation. Throw in a T-Top or overload the boat slightly and all fuel mileage bets go out the window. Interestingly - all the above is also true for a two stroke outfit but with reduced fuel economy - roughly 3.0 mpg or thereabouts.

Now let's look at what happens if we push the engine harder. Did you know that at wide open throttle that same outboard could consume 20-25 gallons per hour? That's what I was getting at when I said the gallons-per-hour rating can be a little confusing for boat owners who are more accustomed to calculating fuel usage in miles-per-gallon.

Now that we understand fuel consumption a little better let's dig into other costs of operation. Four strokes are more fuel efficient but they require more regular servicing, especially crankcase oil changes. Two strokes are not totally immune here, they inject engine lubricant as they burn gasoline. Which costs more?

Actually, the costs of operation are not all that different although you spend it in different ways. Let's assume a four stroke rig and a two stroker are both driven 600 miles.

The average four stroke maintenance cost for oil changes and such will be about $200 out the door, parts and labor included. Premium name-brand two stroke lube runs about $35 per gallon. At average 3.0 mpg you will burn 25% more fuel (200 gal vs. 160) and probably spend about $150 for two stroke lube. You spend a tad more as you drive but the four stroke operator paid more for his engine when new.

As you can see there is actually little difference in the total cost of ownership. What will definitely change the picture is if you run cheap oil. You may think you are saving a few bucks but you will pay the difference and then some down the road. And don't forget the fuel additive to prevent ethanol fuel problems with every fill-up.

Have a great spring season!

Coastal Bend Marine - Port O'Connor, TX
www.coastalbendmarine.com
[email protected]
361-983-4841