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Mercury / Mariner 4 / 5 / 4 Sailpower two-stroke (102 cc) service guide

Oil, gear oil, spark plugs and the service schedule for the Mercury / Mariner 4 / 5 / 4 Sailpower two-stroke (102 cc) (4 to 5 hp, two-stroke), from the factory service manual, plus how we service it in Hawaiʻi.

Models covered: 4 hp (3.0 kW), 5 hp (3.7 kW) and 4 hp Sailpower two-strokes: 1 cylinder, 102 cc (6.2 cid), 55 x 43 mm, water cooled, manual start, premix, forward - neutral - reverse gearcase, integral 2.5 L fuel tank.

Quick answers

What is the fuel to oil ratio for a Mercury / Mariner 4 / 5 / 4 Sailpower two-stroke?
50:1. Automotive unleaded, minimum 87 octane, maximum 10% ethanol (2019).
What spark plug does a Mercury / Mariner 4 / 5 / 4 Sailpower two-stroke use?
NGK BPR7HS-10, or NGK BP7HS-10 (alternate), qty 1. Gap: 1.0 mm (0.040 in.).
How often should a Mercury / Mariner 4 / 5 / 4 Sailpower two-stroke be serviced?
The factory schedule lists: First 25 hours; Every 100 hours or once a year before storing. 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 / Mariner 4 / 5 / 4 Sailpower two-stroke?
The factory schedule gives no replacement interval. 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 / Mariner 4 / 5 / 4 Sailpower two-stroke?
850 RPM in forward gear; low speed mixture screw starts at 1-1/2 turns out (2019).

Maintenance specs

Fuel to oil ratio50:1. Automotive unleaded, minimum 87 octane, maximum 10% ethanol (2019)
Gear oil fill and vent plugsInstall the vent plug first, then take the tube out and install the fill plug
Spark plugNGK BPR7HS-10, or NGK BP7HS-10 (alternate), qty 1
Spark plug gap1.0 mm (0.040 in.)
Idle speed850 RPM in forward gear; low speed mixture screw starts at 1-1/2 turns out (2019)
Zinc anodeOne on the gear housing: replace when approximately 50% consumed, never paint it or its contact surface
Power trim and tiltNone: manual tilt, 6 tilt pin positions, shallow water tilt 32.5°

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. First 25 hours

    Replace: gear case oil, gear case plug gaskets

  2. Every 100 hours or once a year before storing

    Replace: fuel filter, gear case oil, gear case plug gaskets

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

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

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 4/5 Two Stroke service manual, 90-8M0131800, December 2019. 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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