Fuel consumption.

[25931]

It is generally accepted that 2t outboards are thirstier than 4s but can anyone quantify ?

 

[Dellquay13]

What power range are you thinking about 2-10hp? 10-25hp? 30hp+?
My Yamaha F70hp 4t gets about the same mpg (and lph) as my previous Johnson VRO 50hp 2t, but it is a thirsty 70hp 4t as it is tuned for max power from the same engine used across their 50-70hp range. Typically 7mpg or 16lph cruising at 25kts.

At the bottom end of the size range, I wouldn’t be surprised to find that so little petrol is actually used by both 4t and 2t that it goes stale and gets replaced rather than being completely used up.

 

[Plum]

It is generally accepted that 2t outboards are thirstier than 4s but can anyone quantify ?

it all depends on the specific engines you are comparing. A direct fuel injected 2-stroke can be more fuel efficient than a 4-stroke. A small carburetted 2-stroke will be less fuel efficient than a 4-stroke.

Two-stroke versus four-stroke outboard motors

www.solocoastalsailing.co.uk

 

[penfold]

2 strokes are less efficient, incomplete combustion and wasteful of the energy extracted; they are/were used because of the simplicity and lightness.

 

[QBhoy]

Some of the Di 2 strokes are very efficient and occasionally proven more efficient than certainly earlier 4 strokes. Especially the models that have very clever injection delivery. But you could argue that any claims such as this, might be offset by the cost or money spent on the 2 stroke oil required. A 2 stroke man, might counter that again by arguing matters around the cost being less than a 4 stroke when new…or less consumable parts routinely required.

 

[Plum]

Some of the Di 2 strokes are very efficient and occasionally proven more efficient than certainly earlier 4 strokes. Especially the models that have very clever injection delivery. But you could argue that any claims such as this, might be offset by the cost or money spent on the 2 stroke oil required. A 2 stroke man, might counter that again by arguing matters around the cost being less than a 4 stroke when new…or less consumable parts routinely required.

In my experience, modern Di 2-strokes do not use 2-stroke oil that is mixed with the fuel, they use regular engine oil.

 

[ylop]

In my experience, modern Di 2-strokes do not use 2-stroke oil that is mixed with the fuel, they use regular engine oil.

? they don't mix the oil with the fuel (hence why they are direct injection) but they don't use "regular engine oil". Depending on the settings they might burn ordinary 2 stroke oil (in larger quantities) or burn a specialist DI oil more frugally.

 

[Dellquay13]

? they don't mix the oil with the fuel (hence why they are direct injection) but they don't use "regular engine oil". Depending on the settings they might burn ordinary 2 stroke oil (in larger quantities) or burn a specialist DI oil more frugally.

The DI 2t outboards, like the buzzy mopeds tourists rent in Greece, are direct fuel injection, metered oil injection from a separate reservoir and use 2t oil. They can be very frugal compared to the old 2t carburettor engines most people are hanging onto for their tender.
Evinrude use a complicated 2t DI system for their big E-tec outboards with an option to use tiny amounts of their special expensive oil, but the engine has to be programmed for it and you can’t easily swap between the two oil types.

 

[25931]

What power range are you thinking about 2-10hp? 10-25hp? 30hp+?
My Yamaha F70hp 4t gets about the same mpg (and lph) as my previous Johnson VRO 50hp 2t, but it is a thirsty 70hp 4t as it is tuned for max power from the same engine used across their 50-70hp range. Typically 7mpg or 16lph cruising at 25kts.

At the bottom end of the size range, I wouldn’t be surprised to find that so little petrol is actually used by both 4t and 2t that it goes stale and gets replaced rather than being completely used up.

I'm looking for a 40hp. How old does petrol need to be to go stale ?

 

[DownWest]

Hold on a min.. If starting now, you either buy a 4T modern O/B or search around for a decent 2T, likely a bit 'used'. In the small sizes, the consumption is of less interest. Once you move up into 20hp plus, and a main propulsor, the cost of fuel looks more important.

 

[Dellquay13]

I'm looking for a 40hp. How old does petrol need to be to go stale ?

At the rate you will be burning it, you will feel like you are pouring it in from a bucket. Unless you are storing it between trips I wouldn’t worry too much.

I haven’t used my motorboat since 2020 when I bought my yacht (mainly bought to save my huge fuel bill) so I don’t know how well the new E10 fuel stores. If you are looking at a 2t 40hp, it will be pre 2004 and the ending of new 2t motor sales in the EU for leisure use, and may need some seals and pipe work replacing to use E10 unleaded. Premium grade E5 unleaded will still be ok in old 2ts

 

[QBhoy]

In my experience, modern Di 2-strokes do not use 2-stroke oil that is mixed with the fuel, they use regular engine oil.

Never heard of any that use regular engine oil at all. Which models use that ? Any and every I’ve known will use injector specific 2 stroke oil. You sure ?

 

[QBhoy]

In my experience, modern Di 2-strokes do not use 2-stroke oil that is mixed with the fuel, they use regular engine oil.

I’d suggest any of these you know of that have been fed regular engine oil, stop getting used asap. They won’t last long. Amazed they have even ran like that.

 

[PetiteFleur]

My experience of using E10 petrol is that it goes stale quickly - last year I had problems with my Honda mower, Honda 2.3 outboard, 2T strimmer and 2T small generator. Took lawnmower to local mower shop who immediately diagnosed 'stale petrol' . Changed to E5 petrol, cleaned carbs, filled tank with fresh E5 fuel(which really smells of petrol) and had no problems since. Honda now recommend E5 petrol and Honda additive.