20/25 2 stroke vs 4 stroke

martin33100 · 13 September 2018, 15:00

Hi, we have recently squired a nice Avon 3.4M SIB but it has come with a Mercury 4.
Our old 3.8M had a Yam 15 2 stroke but any more than 2 and it was under powered.
Our 3.4 is rated at 25hp and from memory most 20/25's are the same engine/same weight so I just as well go for a 25.

I like the lightweight and quick throttle response from a nice 2 stroke but even the last models (unless I try and buy a new commercial one) are now 12 years old.

Any advice will be greatly appreciated.

Fenlander · 13 September 2018, 15:49

I would have no fear of 12-15yr old 2-strokes. Many of them have low hours and been kept in great condition dry stored by leisure users.

jeffstevens763@g · 13 September 2018, 17:03

i run a suzuki 25 3 cylinder 2015 you will read in other threads i'm having a bit of trouble with it but that doesn't detract from the fact it's a brilliant engine propped down to 10 1/4 x 10 and its as crisp as you like in perfect conditions it will do 21 knots with that prop best i have had is 22/23 knots with a 10 1/4 x 11 prop but speed is no good to me i need quick response in heavy seas to maintain the plane. current fuel consumption is 4.6 KM/L fully loaded with camping kit and 81 ltrs of fuel. engine weighs 61 kg and has a big cowl for the 3 cylinders i wouldnt look at a two stroke now for two reasons only the smell & the constant wine have enough of that with the wife

Fenlander · 13 September 2018, 17:37

>>>wouldn't look at a two stroke now for two reasons only the smell & the constant wine

Fair point Jeff and I voted that way with my wallet paying a few hundred more for the current new Mariner 10hp 4-stroke than the best 2006 Mercury 15hp 2-stroke you'd find which is actually a whisker lighter than the 10hp 4-stroke.

I kept 4-stroke having got used to the exceptionally quiet trolling, fuel consumption (more to enable a smaller tank rather than cost), ease of disposing of unused fuel after trips in daughters car, slightly reduced chance of fuel contamination and less faff with no mixing needed.

But from a reliability perspective I'd be happy to say a mint 2006 2-stroke will probably run at least another 10 trouble free years with basic easy DIY maintenance.

And if circumstances dictated a return to 2-stroke I would go back.

martin33100 · 13 September 2018, 18:04

Thanks for the replys.
I did my aprenticeship with one of the diesel manufacturers working on 2 and 4 stroke diesels so I know the basics.
I remember a few years back talking to one of the outboard repairers about reliability and he said then the well looked after 2 strokes were out lasting the 4's.

Fenlander · 13 September 2018, 18:39

Slight simplification but all a 2-stroke owner has to do to ensure basic engine condition is feed it with the fuel/oil mix. The 4-strokes are candidates for missed oil & filter changes plus running with low/no oil or storing/travelling the wrong way getting oil places it shouldn't be and losing it from where it should be.

This introduces a risk of what I call owner induced wear/failure on the 4-strokes.

jeffstevens763@g · 13 September 2018, 18:50

Quote:

Originally Posted by Fenlander

>>>wouldn't look at a two stroke now for two reasons only the smell & the constant wine

Fair point Jeff and I voted that way with my wallet paying a few hundred more for the current new Mariner 10hp 4-stroke than the best 2006 Mercury 15hp 2-stroke you'd find which is actually a whisker lighter than the 10hp 4-stroke.

I kept 4-stroke having got used to the exceptionally quiet trolling, fuel consumption (more to enable a smaller tank rather than cost), ease of disposing of unused fuel after trips in daughters car, slightly reduced chance of fuel contamination and less faff with no mixing needed.

But from a reliability perspective I'd be happy to say a mint 2006 2-stroke will probably run at least another 10 trouble free years with basic easy DIY maintenance.

And if circumstances dictated a return to 2-stroke I would go back.

With out dought a well looked after 2 stroke are worth thier Buck, gurnard's 25 mariner 14 years old I believe never missed a beat around Skye and using 10% more fuel than me certantly a contender but under his own admission 5or6 hours of it wining does get to him. The only thing I don't like about my engine is a timing belt sooner had a chain or a no interfearance engine if it breaks just my thing. Maintenance wise when my warranty runs out I will change the oils filters as per including the belt my self. Just treat same as the car with service intervals increasing on cars I think we get too hung up with outboards OMO