Mercury 75 / 80 / 90 / 100 / 115 FourStroke 2.1 L (and 115 Pro XS, SeaPro) service guide

Quick answers

How much oil does a Mercury 75 / 80 / 90 / 100 / 115 FourStroke 2.1 L take?

5.2 L (5.5 US qt) with filter.

What engine oil does a Mercury 75 / 80 / 90 / 100 / 115 FourStroke 2.1 L use?

Mercury or Quicksilver NMMA FC-W SAE 10W-30 4-Stroke for all temperatures; 25W-40 mineral or synthetic blend allowed. SeaPro (8M0231643 only): 25W-40 recommended; 10W-30 at 0 °C (32 °F) or below.

What gear oil does a Mercury 75 / 80 / 90 / 100 / 115 FourStroke 2.1 L use, and how much?

High Performance Gear Lubricant. Quantity: Standard 800 ml (27.1 fl oz); Command Thrust / SeaPro right hand 810 ml (27.4 fl oz), left hand 790 ml (26.7 fl oz).

What spark plug does a Mercury 75 / 80 / 90 / 100 / 115 FourStroke 2.1 L use?

NGK ZFR5F, qty 4, 16 mm hex. Gap: 0.8 mm (0.032 in).

How often should a Mercury 75 / 80 / 90 / 100 / 115 FourStroke 2.1 L 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 75 / 80 / 90 / 100 / 115 FourStroke 2.1 L?

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 / 80 / 90 / 100 / 115 FourStroke 2.1 L?

700 r/min at operating temperature; 700 to 800 r/min cold warm-up; up to 800 r/min idle charge (low battery).

What is the propeller nut torque on a Mercury 75 / 80 / 90 / 100 / 115 FourStroke 2.1 L?

75 N·m (55.3 lb·ft); bend the retainer tabs.

Maintenance specs

Engine oil	Mercury or Quicksilver NMMA FC-W SAE 10W-30 4-Stroke for all temperatures; 25W-40 mineral or synthetic blend allowed. SeaPro (8M0231643 only): 25W-40 recommended; 10W-30 at 0 °C (32 °F) or below
Engine oil quantity	5.2 L (5.5 US qt) with filter
Oil filter	Oil the gasket; screw on until the gasket touches the base, then 3/4 to 1 turn
Oil drain valve	15 N·m (132.8 lb·in). Loosen no more than 2 1/2 turns to drain; overtightening can damage the oil sump
Gear lubricant	High Performance Gear Lubricant
Gearcase capacity	Standard 800 ml (27.1 fl oz); Command Thrust / SeaPro right hand 810 ml (27.4 fl oz), left hand 790 ml (26.7 fl oz)
Gearcase fill and vent screws	11.3 N·m (100 lb·in), including the SeaPro upper vent, front fill/drain and lower vent
Gear housing leak test	103.4 kPa (15 psi) held 15 minutes, without lubricant (tester FT8950)
Spark plug	NGK ZFR5F, qty 4, 16 mm hex
Spark plug gap	0.8 mm (0.032 in)
Spark plug torque	27 N·m (20 lb·ft), or finger tight plus 1/4 turn
Idle speed	700 r/min at operating temperature; 700 to 800 r/min cold warm-up; up to 800 r/min idle charge (low battery)
Thermostat	Starts to open 46.1 to 51.7 °C (115 to 125 °F); fully open 65.6 °C (150 °F); stroke at least 7.62 mm (0.30 in)
Water pressure	5 to 30 kPa (0.7 to 4.4 psi) at 650 r/min idle; 80 to 300 kPa (11.6 to 43.5 psi) at 5800 r/min
Anode screws	Trim tab anode screw 54 N·m (40 lb·ft); gearcase side anodes M6 x 40 6.8 N·m (60 lb·in); transom bracket anode M6 x 25 8 N·m (70.8 lb·in)
Propeller nut	75 N·m (55.3 lb·ft); bend the retainer tabs
Power trim fluid	Power Trim and Steering Fluid or ATF Dexron III; level with the bottom of the fill hole, tilted full up. Cap 2.5 N·m (22 lb·in); manual release valve 4 N·m (35 lb·in)
Valve clearance (camshaft to roller), cold	IN 0.075 ± 0.025 mm (0.003 ± 0.001 in); EX 0.150 ± 0.025 mm (0.006 ± 0.001 in); ball stud locknut 20 N·m (177 lb·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 or once a year

   Replace: engine oil, oil filter, oil drain plug gasket, gear case oil, gear case plug gaskets, propeller cotter pin

   Check: fuel filter, 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, gear case oil, gear case plug gaskets, propeller cotter pin, water pump impeller

   Check: fuel filter, thermostat, anodes

3. Every 300 hours or 3 years

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

   Check: fuel filter, 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 75/80/90/100/115/115 Pro XS FourStroke 2.1L service manual, 90-8M0231643. Specs can change by model year and serial number, so always confirm your exact model from the serial tag on the clamp bracket.