REVIEW: TOHATSU MFS6C

Released in 2000 and also sold as the Mariner / Mercury F6, Tohatsu’s 123cc MFS6A was the first single-cylinder four-stroke six in Australia. It was followed by Suzuki’s DF6

All three engines were designed to provide low-emission operation while remaining relatively light. They all have single-cylinder OHV engines, with the main differences being piston displacement. All have pressure lubrication, CD ignition with electronic timing advance, and the option of integral or remote fuel tanks, or both.

THE NITTY GRITTY

The Tohatsu MFS6C, released mid-2011, is the first of these engines to have an upfront gearshift and a much longer tiller arm. There are still six trim positions with a single shallow-water setting and an automatic full-tilt lock and reverse lock. The upper cowl is more rounded than the 6A, with an improved air intake flow.

As with its predecessor, only a 12lt remote fuel tank is available.

A 12V, 5A unregulated alternator is optional. The engine still develops 5.9hp at 5500rpm, with a wide open throttle (WOT) range of 5000-6000rpm and a 2.15:1 gear ratio. The dry weight is 25.6kg. Tohatsu still hasn’t fitted a carry handle to the aft end of the lower cowl, so you need two hands to carry it instead of just one for the DF6 and F6C. This is a real pain over longer distances.

ON THE WATER

In June the Aussie Tohatsu distributor, Lakeside Marine, provided me with a new MFS6C for extended evaluation on my 2003 Sea Jay 3.4 Punt — the same hull I’ve also tested the DF6 and F6C on.

Over an initial two-week test period the borrowed MFS6C was carefully run in before performance trials commenced. It started easily hot or cold because the choke is crosslinked with the throttle. That said, on each cold start it blew some oil smoke for the first minute or so, just like the 6A model I borrowed in 2000.

Spinning the standard 8in-pitch, semi-weedless alloy prop and carrying a total of 290kg, including two adults and fishing tackle, the MFS6C did a very good job of pushing the load. Although trolling operation was limited to no more than 10 minutes at a time (first 10 hours), it ticked over steadily with little vibration through the hull. At mid-range rpm the vibration was on par with the DF6 and lower than the F6C, but at or near WOT the vibration was greater than the F6C.

The minimum planing speed on this engine is also my recommended maximum cruising speed (to prevent powerhead damage), achieved at three-quarters throttle.

Although the F6C was quicker at WOT than the MFS6C, the Tohatsu outperformed the DF6, most likely due to the fitting of a prop where the pitch is greater than the diameter. All props used on planing hulls should be designed this way in order to achieve maximum efficiency — the DF6’s prop loses efficiency due to its diameter being bigger than its pitch.

Around a loop of normal cruising including 10 per cent WOT and 40 per cent trolling operation, averaging 4kt (7.5kmh), the Tohatsu used 0.52L/hr — 10 per cent less than the DF6 (and the F6C under identical test conditions). However, because of its older design, the MFS6C has 70 per cent higher exhaust emissions than the DF6 (no figures are available for the F6C), but it still gains an OEDA “3 Star” exhaust emissions rating.

Powerhead access is better than the DF6 and F6C, which also have integral fuel tanks, and the MFS6C appears easy to maintain with the spark plug, carbie / choke linkages and oil filler plug / dipstick all easily accessed. Tohatsu recommends servicing the MFS6C every 50 hours, or 12 months after the initial 10-hour check-up. However, as the sump holds only 0.45lt, I’d change the oil every 50 hours or every six months.

THE WRAP

Tohatsu has done a top job of upgrading its four-stroke six to make it more user-friendly. When trolling with a rod in one hand, being able to hold the tiller arm and shift gear with the other is a real bonus, and the overall fuel efficiency is excellent.

This Japan-made unit has an excellent build quality, on par with the French-made F6C and above the Thai-built DF6. As of July 2011 the shortshaft MFS6C retailed for A$1851, with a spare prop costing A$140. It carries a three-year recreational usage warranty.

TOHATSU MFS6C SPECS

TYPE Single-cylinder four-stroke

RATED BHP/MHP* 5.9 at 5500rpm

REC. WOT RANGE 5000 to 6000rpm

DISPLACEMENT 123cc

BORE X STROKE 59 x 45mm

GEAR RATIO 2.15:1

WEIGHT 25kg

OEDA STARS 1

*Brake horsepower/metric horsepower or PS

SEA TRIALS

2.3kts (4.3kmh) @ 1300rpm (trolling) using 0.16lt/h

12.3kts (22.8kmh) @ 5100rpm (min. planing) using 1.7lt/h

15.3kts (28.3kmh) @ 5740rpm (WOT) using 2.2lt/h

THE COMPETITION