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Mercury OptiMax 75 / 90 / 115 / 125 (1.5L) service guide

Oil, gear oil, spark plugs and the service schedule for the Mercury OptiMax 75 / 90 / 115 / 125 (1.5L) (75 to 125 hp, two-stroke), from the factory service manual, plus how we service it in Hawaiʻi.

Models covered: Mercury 75, 90, 115, 115 Pro XS and 125 OptiMax direct fuel injection 2-stroke, 3 cylinder 1.5L, serial 0T801000 and above.

Quick answers

What two-stroke oil does a Mercury OptiMax 75 / 90 / 115 / 125 use?
TC-W3 Premium Plus or OptiMax 2-Cycle Outboard Oil.
What gear oil does a Mercury OptiMax 75 / 90 / 115 / 125 use, and how much?
Premium Gear Lubricant; Premium or High Performance. Quantity: 665 ml (22.5 fl oz).
What spark plug does a Mercury OptiMax 75 / 90 / 115 / 125 use?
NGK PZFR6H or IZFR5J, gap 0.8 mm (0.031 in); qty 3.
How often should a Mercury OptiMax 75 / 90 / 115 / 125 be serviced?
The factory schedule lists: Every 100 hours or once a year; Every 300 hours or 3 years. 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 75 / 90 / 115 / 125?
The factory schedule says to replace it at 300 hours. In Hawaiʻi's warm salt water we replace it every 200 hours or 1 year, whichever comes first, because a worn impeller is the most common cause of overheating.
What is the idle speed of a Mercury OptiMax 75 / 90 / 115 / 125?
650 ± 25 r/min. Not adjustable; check with the CDS.
What is the propeller nut torque on a Mercury OptiMax 75 / 90 / 115 / 125?
75 N·m (55 lb·ft); bend three tabs. FloTorq III hub required.

Maintenance specs

Injection oilTC-W3 Premium Plus or OptiMax 2-Cycle Outboard Oil
Gear lubePremium Gear Lubricant; Premium or High Performance
Gearcase capacity665 ml (22.5 fl oz)
Drain and vent screws (3)6.8 N·m (60 lb·in)
Gearcase pressure test (no lube)69 to 83 kPa (10 to 12 psi) for 5 minutes
Spark plugNGK PZFR6H or IZFR5J, gap 0.8 mm (0.031 in); qty 3
Spark plug torqueFinger tight plus 1/4 turn, or 27 N·m (20 lb·ft)
Idle speed650 ± 25 r/min. Not adjustable; check with the CDS
ThermostatStamped 143°; starts to open 60 to 62.7 °C (140 to 145 °F); fully open 73.8 °C (165 °F); lift at least 3.302 mm (0.130 in)
Water pressureIdle (625 r/min) 20.6 to 41.3 kPa (3 to 6 psi); WOT (5750 r/min) 75.8 to 96.5 kPa (11 to 14 psi); poppet opening 48.3 to 62.1 kPa (7 to 9 psi)
AnodesGearcase side anode M6 x 40 screw and nut 6.8 N·m (60 lb·in); transom bracket anode M6 x 25 screws 7.9 N·m (70 lb·in)
Propeller nut75 N·m (55 lb·ft); bend three tabs. FloTorq III hub required
Power trim fluidPower Trim and Steering Fluid or ATF (Dexron III)

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, spark plugs, gear case oil, gear case plug gaskets

    Check: 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

  3. Every 300 hours or 3 years

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

    Check: spark plugs, anodes

We replace the water pump impeller at every service from 200 hours up, which can be sooner than the factory schedule, because of Hawaiʻi’s warm salt water.

Source: Mercury 75/90/115/125 and 115 Pro XS OptiMax service manual, 90-8M0047659. 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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