words - Andrew Norton
With all the focus on the high-tech new-generation powerplants, it's easy to forget that in some applications 'conventional' two-strokes are an excellent option.

Such is the case with Mercury Marine's 175 EFI a cost-effective compromise between the carbie and Optimax models. Andrew Norton.

Since the introduction of Mercury Marine's Optimax range of motors, the company's existing V-six line-up has been largely overlooked. This is a shame, because in their latest EFI form, these models offer good value, easier starting and marginally lower fuel consumption than the carbie models without the complication of direct injection.

Sure they don't offer the much-vaunted benefits of the Optimax powerplants, but compared to the carbie models, the EFIs are still a full generation ahead.

Theses are engines in which automotive-type EFI injects fuel upstream of the combustion chamber (at the reed valves), unlike the Optimax where fuel is injected directly into the combustion chamber like a diesel engine.

Mercury Marine's EFI models were introduced locally in the late 1980s and although initially there were teething problems, they offer a lot a benefits over carbie models.

The electronic management system keeps the motor in peak tune. It incorporates features such as the turn-key starting like a car (without having to worry about over or under choking the motor) and fast-idle warm-up which helps the motor quickly reach normal operating temperature.

The EFI also maintains the correct air/fuel ratio according to barometric pressure. On hot and damp days the motor won't run rich or have hot starting problems due to vapour lock.

Oil is mixed with the fuel at the reed valves and varies in ratio from 100:1 at Dead Slow Troll (DST) to 50:1 at Wide Open Throttle (WOT).

The 175 EFI uses the same 2507cc powerhead as the 150 EFI and 200 EFI models and carbie 175/200, which in turn is bored-out version of the 1998cc powerhead of the carbie 135 and early 150.

The 175 EFI retails for only 7% more than the carbie 175 and is 3% heavier, although it weighs 7% less than the Optimax 135/150. In its 150 EFI form, it is 6% cheaper than the Optimax 150.

Supplied by Black Pete Marine of Seaforth (NSW) and fitted to a Markham Bonito 622 Profish, the 175 EFI provided as much power as you'd ever need on this hull.

It started instantly hot or cold and reached normal operating temperature within a couple of minutes from cold. Once warm, it idled at a relatively low 700rpm in gear, though it was significantly rougher than the Optimax 135 sampled recently. After a few minutes of idling it smoked as much as a carbie motor, but above 1000rpm this disappeared.

Spinning an 18inch pitch stainless steel prop and pushing an estimated total of 1350kg (including two adults) it planed us on only 2800 revs and 30kmh, while at 4000 revs we averaged 52kmh consuming 41lt/h. At WOT the Merc averaged 80kmh on 5500 revs across a 30cm chop. The fuel consumption was a fairly high 69lt/h, but all the same was not bad, considering the additional windage of outriggers, a rocket launcher atop the canopy and clears on the test boat.

There was significant prop ventilation in hard-over figure of eights and coming out of the hole there was a slight miss at 2500rpm with higher noise levels than, say, Yamaha's 175, from these revs up.

The 175 EFI is straight forward to service with intervals recommended every 100 operating hours or yearly (also for the waterpump impeller) after the first 20 and 50 hours.

The test motor had clocked up 129 hours of mostly offshore operation, and surprisingly for a Mercury Marine product there was a significant amount of corrosion in areas not expected. It was disappointing to see rust on the SS prop and forward lower unit retaining bolt, despite the fitting of a transom bracket zinc anode (almost corroded away). Still, it is hard to pass final judgement on a motor's saltwater corrosion resistance unless you really know exactly how it's been treated.

This aside, the 175 EFI is good value for money. The standard of castings and paint finish is excellent and the motor is well engineered just as you'd expect from Mercury Marine!

Mercury 175 EFI
Type: Loop-charged 60° fuel-injected V-six, two stroke
Prop hp/rpm: 175/5300
WOT rev range: 5000-5600
Piston displacement (cc): 2507
Bore x stroke (mm): 88.9 x 67.3
Ignition system: Electronic engine management
Charging circuit (amps): 40 regulated
Fuel: Straight ULP
Oil: TC-W3
Oil tank capacity (litres): 11.4
Gear ratio: 1.87:1
Transom height (XL, inches): 25
Weight (kg): 186
Rec. retail: $19,120
Spare S/S prop: $933
Waterpump impeller: $21
Servicing costs*
Year One: $405
Year Two, etc: $165
*As per manufacturer's recommended schedule but excluding parts. Spares and servicing prices (as of June 1999) from Tomos Marine, Marks Point (NSW), tel (02) 4945 3202.

Published : Wednesday, 1 September 1999

Prices and specifications supplied are for the market in Australia only and were correct at time of first publication. makes no warranty as to the accuracy of specifications or prices. Please check with manufacturer or local dealer for current pricing and specifications.

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