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Mercury 75 / 90 / 115 FourStroke EFI (4 cylinder 1.7 L, serial 1B366823 to 2B095048) service guide

Oil, gear oil, spark plugs and the service schedule for the Mercury 75 / 90 / 115 FourStroke EFI (4 cylinder 1.7 L, serial 1B366823 to 2B095048) (75 to 115 hp, four-stroke), from the factory service manual, plus how we service it in Hawaiʻi.

Models covered: Mercury 75, 90 and 115 FourStroke EFI (80, 100 and 115 in the EU), serial 1B366823 to 2B095048. the ending serial is where the 2.1 L manual starts (2B095049). 4 cylinder, 1.7 L (105.6 cu in), 16 valve double overhead cam driven by a timing chain, electronic fuel injection, integrated dry sump. One gear case size, 710 ml; the 115 changed from a 2.07:1 to a 2.33:1 gear ratio at serial 1B739661.

Quick answers

How much oil does a Mercury 75 / 90 / 115 FourStroke EFI take?
5 liter (5.3 US qt) with filter replacement; Fill to the midpoint of the cross hatched region of the dipstick, not to the top of it.
What engine oil does a Mercury 75 / 90 / 115 FourStroke EFI use?
Mercury or Quicksilver NMMA FC-W certified Synthetic Blend 25W-40 multi-viscosity 4-Stroke Outboard Oil.
What gear oil does a Mercury 75 / 90 / 115 FourStroke EFI use, and how much?
High Performance Gear Lubricant. Quantity: Approximately 710 ml (24 fl oz), both gear ratios.
What spark plug does a Mercury 75 / 90 / 115 FourStroke EFI use?
NGK LFR4A-E, qty 4 (hex 16 mm, 14 mm thread). Gap: 0.8 mm (0.032 in).
How often should a Mercury 75 / 90 / 115 FourStroke EFI be serviced?
The factory schedule lists: Every 100 hours of use or once yearly, whichever occurs first; Every 300 hours of use or three 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 75 / 90 / 115 FourStroke EFI?
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 75 / 90 / 115 FourStroke EFI?
700 ± 50 rpm, all models. Full throttle range 5000 to 6000 rpm (75/90, EU 80/100) and 5800 to 6400 rpm (115).
What is the propeller nut torque on a Mercury 75 / 90 / 115 FourStroke EFI?
75 Nm (55 lb-ft); bend three tabs of the retainer into the thrust hub grooves.

Maintenance specs

Engine oilMercury or Quicksilver NMMA FC-W certified Synthetic Blend 25W-40 multi-viscosity 4-Stroke Outboard Oil
Engine oil quantity5 liter (5.3 US qt) with filter replacement; Fill to the midpoint of the cross hatched region of the dipstick, not to the top of it
Oil filterApply a film of clean oil to the gasket (no grease); screw on until the gasket contacts the base, then tighten 3/4 to 1 turn.
Engine oil drain plug23 Nm (17 lb-ft), with gasket; lubricate the seal on the drain plug with oil
Gear lubeHigh Performance Gear Lubricant
Gear lube quantityApproximately 710 ml (24 fl oz), both gear ratios
Gear lube fill/drain, front vent and rear vent plugs3 drain screws (fill/drain, front vent, rear vent), each with a sealing washer, 8.5 Nm (75 lb-in). Install a new sealing washer on the fill and vent screws
Gear case leak test pressure69 to 83 kPa (10 to 12 psi) for 5 minutes, before gear lubricant is added
Spark plugNGK LFR4A-E, qty 4 (hex 16 mm, 14 mm thread)
Spark plug gap0.8 mm (0.032 in)
Spark plug torque27 Nm (20 lb-ft); or finger tight then 1/4 turn. Pencil coil retaining screws 10 Nm (88.5 lb-in) with Loctite 271
Idle speed700 ± 50 rpm, all models. Full throttle range 5000 to 6000 rpm (75/90, EU 80/100) and 5800 to 6400 rpm (115)
ThermostatStarts to open at 46.1 to 51.7 °C (115 to 125 °F); full open 65.5 °C (150 °F); piston height at full open 7.62 mm (0.300 in)
Fuel filtersTwo filters. Low-pressure filter: checked for contaminants every 100 hours and replaced if required; install with the arrow toward the engine. High-pressure in-line filter: replaced every 300 hours or three years; it is under pressure and the pressure must be released first.
AnodesAnodes on each side of the gear case and one on the bottom of the transom bracket. Gear housing anode screw (M6 x 40) 7 Nm (62 lb-in). The trim tab is painted and is not an anode; trim tab retaining screw 30 Nm (22 lb-ft)
Propeller nut75 Nm (55 lb-ft); bend three tabs of the retainer into the thrust hub grooves
Power trim fluidPower Trim and Steering Fluid, or automatic transmission fluid (ATF, Dexron III) if not available. Tilt full up on the tilt support lever; level even with the bottom of the fill hole
Valve lashIntake 0.150 to 0.270 mm (0.0059 to 0.0106 in); exhaust 0.350 to 0.470 mm (0.0137 to 0.0185 in)

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 of use or once yearly, whichever occurs first

    Replace: engine oil, oil filter, oil drain plug gasket, spark plugs, fuel filter, gear case oil, gear case plug gaskets

    Check: thermostat, anodes

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

    Replace: engine oil, oil filter, oil drain plug gasket, spark plugs, fuel filter, gear case oil, gear case plug gaskets, water pump impeller

    Check: thermostat, anodes

  3. Every 300 hours of use or three years

    Replace: engine oil, oil filter, oil drain plug gasket, spark plugs, fuel filter, gear case oil, gear case plug gaskets, water pump impeller

    Check: thermostat, 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 FourStroke EFI service manual. 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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