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Mercury OptiMax 135 / 150 (2.5 L, 1998 to 1999) service guide

Oil, gear oil, spark plugs and the service schedule for the Mercury OptiMax 135 / 150 (2.5 L, 1998 to 1999) (135 to 150 hp, two-stroke), from the factory service manual, plus how we service it in Hawaiʻi.

Models covered: Mercury 135 and 150 OptiMax (Model 135/150 DFI) direct injected 2-stroke V6, 153 cu in (2508 cc), starting model year 1998 thru 1999, serial 0G590000 to 0G960499. Gear ratios 2.00:1 (135) and 1.87:1 (150), optional high altitude 2.30:1 (135) and 2.00:1 (150).

Quick answers

What two-stroke oil does a Mercury OptiMax 135 / 150 use?
TC-W3 Premium Plus 2 Cycle Outboard Oil.
What gear oil does a Mercury OptiMax 135 / 150 use, and how much?
Premium Gear Lubricant. Quantity: 22.5 fl oz (665.4 ml); 665 ml; "approximately 22.5 fl oz (666 ml)"; same for the 1.87:1, 2.00:1 and 2.30:1 gear cases.
What spark plug does a Mercury OptiMax 135 / 150 use?
NGK PZFR5F-11 or NGK ZFR5F-11; gap 0.040 in (1.0 mm); qty 6.
How often should a Mercury OptiMax 135 / 150 be serviced?
The factory schedule lists: Every 100 hours or once a year. In Hawaiʻi's salt water we do a full yearly service every 200 hours or 1 year, whichever comes first, and a new engine needs its first (break-in) service.
When should the water pump impeller be replaced on a Mercury OptiMax 135 / 150?
The factory schedule says to replace it at 100 hours, and we follow that. In any case we never let it go longer than a year in Hawaiʻi's salt water.
What is the idle speed of a Mercury OptiMax 135 / 150?
550 ± 25 RPM. Full throttle 5000 to 5600 RPM.
What is the propeller nut torque on a Mercury OptiMax 135 / 150?
Minimum of 55 lb·ft (74.5 N·m); bend three tabs of the tab washer; retighten after first use.

Maintenance specs

Injection oilTC-W3 Premium Plus 2 Cycle Outboard Oil
Gear lubePremium Gear Lubricant
Gearcase capacity22.5 fl oz (665.4 ml); 665 ml; "approximately 22.5 fl oz (666 ml)"; same for the 1.87:1, 2.00:1 and 2.30:1 gear cases
Drain (magnetic) and grease filler screws60 lb·in (7 N·m), with sealing washers; the fill instructions say to install new gaskets on the fill and vent screws
Spark plugNGK PZFR5F-11 or NGK ZFR5F-11; gap 0.040 in (1.0 mm); qty 6
Spark plug torqueFinger tight plus 1/4 turn, or 20 lb·ft (27 N·m)
Idle speed (in gear)550 ± 25 RPM. Full throttle 5000 to 5600 RPM
Water pressureIdle 1.0 to 3.0 psi (6.8 to 20.5 kPa); poppet valve opening 4 to 9 psi (27.4 to 61.6 kPa); WOT 12.0 psi (82.1 kPa) minimum
Water separating fuel filterReplace every 100 hours or once a year. Spin-on with a water sensor wire at the bottom; oil the sealing ring, tighten by hand, squeeze the primer bulb firm and check for leaks
AnodesGearcase anode screw (M6 x 40) nut 60 lb·in (7 N·m); screw listed with the trim tab 25 lb·ft (34 N·m). Two gearcase anodes and one on the bottom of the transom bracket
Propeller nutMinimum of 55 lb·ft (74.5 N·m); bend three tabs of the tab washer; retighten after first use
Power trim fluidPower Trim & Steering Fluid; if not available, automotive ATF. Level even with the bottom of the fill hole, tilted full up on the tilt support lock
Alternator / air compressor beltTension is kept by a belt tensioner assembly.

Service schedule

The factory maintenance intervals, with what is replaced and what is checked at each. Rows marked Hawaiʻi are our shop's yearly service for salt water use.

  1. Every 100 hours or once a year

    Replace: fuel filter, air filter, gear case oil, gear case plug gaskets, water pump impeller

    Check: spark plugs, anodes

  2. Every 200 hours or 1 year (our Hawai‘i yearly service) Hawai‘i

    Replace: fuel filter, air filter, gear case oil, gear case plug gaskets, water pump impeller

    Check: spark plugs, anodes

Source: Mercury 135/150 OptiMax Direct Fuel Injection service manual, 90-855347R02. Specs can change by model year and serial number, so always confirm your exact model from the serial tag on the clamp bracket.

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