torquing
talk
WITH ANDREW NORTONOld Faithful
STILL POPULAR AFTER 35 YEARS ... EXCEPT WITH THE REGULATORS
T
ohatsu’s 18 has
been a success
story since the
first model,
the M18A, was
released in 1982. As with
other Tohatsu outboards of
the time, it had an above-
prop exhaust that made prop
swapping easy but reduced
the exhaust system’s ability
to scavenge exhaust gases.
This was rectified in the
mid-80s with a through-
prop hub exhaust design
that’s carried on in the
still-current M18E2 model
(released 1999).
Why has the 18 has been
one of Tohatsu’s most
popular models? It develops
significantly more torque
than a 15 but weighs way
less than a 20 – all the
20s are de-rated 25s. This
allows it to provide excellent
performance on short-shaft
tinnies in the 3.8-metre
range without seriously
affecting freeboard at the
transom. Though it’s still
fairly hefty, most of us
can lift the M18E2 onto the
transom of a tinny without
incurring permanent back
injury, something that can’tbe said for 20hp outboards.
Since 1989 I’ve tested four
18s and, due to modifications
to combustion chamber
design, each model has been
better than its predecessor.THE NITTY GRITTY
The 18 has a twin-cylinder
loop-charged powerhead
with CD ignition and simple
mechanical timing advance.
The powerhead is a bored-
out version of the 247cc
Tohatsu 15 but at 294cc
has a way smaller piston
displacement than the
395cc Yamaha 20 or long-
discontinued 400cc Mariner
and Mercury 20s, the latter
also 10kg heavier.
Unlike the Tohatsu M8B/
M9.8B, the 18 was designed
for commercial operators
and has an auxiliary
cooling-water intake under
the anti-ventilation plate
as well as the main intake
just above the gearcase
torpedo. Should the main
intake become clogged with
weed, this ensures at least
some water will reach the
powerhead.
The thermostat is
mounted separately to thecylinder head and can be
easily replaced, and there
are rod-operated throttle
linkages, which are more
reliable than push-pull
cables. Finally there’s an
easily cleaned bowl-type
fuel filter instead of a
disposable in-line unit. So
while the 18 may appear to
be simply a larger version
of its smaller counterpart,
it’s actually a very different
engine. Really the only
similarities are the side
gearshift, and the six
trim positions and single
shallow-water drive setting.
An unregulated six-amp
alternator is optional, as is
electric starting for wimps.
The 18 requires only a firm
two-hand pull when cold,
and one hand when warm
to fire it up I see no need for
electric starting.
Powerhead access is good,
with the sparkplugs and
fuel filter easily reached.
Servicing intervals are every
50 hours or annually after
the first service at 10 hours,
and the recreational usage
warranty is three years. The
break-in period is 10 hours
on 25:1, with 50:1 after that,and the recommended oil
is semi-synthetic Valvoline
Outboard Oil.ON THE WATER
I tested the first model on
a 3.6m Sea Al Super Skua
tinny but even with a
10in-pitch prop the engine
was significantly under
propped. Pushing a total of
285kg including two adults
(I was way lighter then) and
fishing tackle it ran out to a
very scary 27kt.
The next model, in 1992,
was an M18B2 mounted
on my 5.5m Asquith LFB
and swinging an 8.8in-
pitch prop gave about as
much power as would ever
be needed on this round-
bilge semi-planing hull.
As with the first engine,
no revs were picked up on
my portable tachometer
at that time but pushing a
total of 610kg including two
adults and fishing nets, at
two-thirds throttle opening
the 18 averaged 14.7kt,
using 8.5L/h, while at WOT
achieved 15.3kt and 9.9L/h.
In the years leading up to
the current M18E2 Tohatsu
redesigned the combustion74 tradeaboat.com.au