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Mercury 75 / 90 EFI FourStroke (1.6 L, 2005 on) service guide

Oil, gear oil, spark plugs and the service schedule for the Mercury 75 / 90 EFI FourStroke (1.6 L, 2005 on) (75 to 90 hp, four-stroke), from the factory service manual, plus how we service it in Hawaiʻi.

Models covered: Mercury 75 and 90 FourStroke EFI, 4 cylinder 1.6 L, model year 2005 on, serial 1B172291 to 1B366822. The 2.1 L 75 to 115 has its own sheet.

Quick answers

How much oil does a Mercury 75 / 90 EFI FourStroke take?
4.3 L (4.6 US qt) without filter; 4.5 L (4.8 US qt) with filter.
What engine oil does a Mercury 75 / 90 EFI FourStroke use?
SAE 10W-30 all temperatures; 25W-40 above 4 °C (40 °F).
What gear oil does a Mercury 75 / 90 EFI FourStroke use, and how much?
Premium Gear Lubricant; Premium or High Performance.
What spark plug does a Mercury 75 / 90 EFI FourStroke use?
NGK LFR5A-11. Gap: 1.1 mm (0.043 in).
How often should a Mercury 75 / 90 EFI FourStroke be serviced?
The factory schedule lists: Every 100 hours or once a year; Every 300 hours or 3 years; Every 400 hours. 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 EFI FourStroke?
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 EFI FourStroke?
Forward 700 ± 50 r/min; neutral 750 ± 50 r/min.
What is the propeller nut torque on a Mercury 75 / 90 EFI FourStroke?
75 N·m (55 lb·ft); bend three tabs.

Maintenance specs

Engine oilSAE 10W-30 all temperatures; 25W-40 above 4 °C (40 °F)
Engine oil quantity4.3 L (4.6 US qt) without filter; 4.5 L (4.8 US qt) with filter
Oil filter3/4 to 1 turn after the gasket touches
Oil drain plug24 N·m (17.5 lb·ft)
Gear lubricantPremium Gear Lubricant; Premium or High Performance
Gearcase drain and vent screwsDrain screw 7 N·m (60 lb·in); vent screw 6.7 N·m (60 lb·in)
Gearcase leak test69 to 83 kPa (10 to 12 psi) for 5 minutes
Spark plugNGK LFR5A-11
Spark plug gap1.1 mm (0.043 in)
Spark plug torque25 N·m (18 lb·ft)
Idle speed, warmForward 700 ± 50 r/min; neutral 750 ± 50 r/min
ThermostatNo lift below 58 °C (136 °F); at least 4.3 mm (0.17 in) above 62 °C (144 °F). The parts list shows a 60 °C (140 °F) thermostat
Propeller nut75 N·m (55 lb·ft); bend three tabs
Valve clearance, coldIN 0.20 ± 0.03 mm (0.008 ± 0.001 in); EX 0.34 ± 0.03 mm (0.013 ± 0.001 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, spark plugs, gear case oil, gear case plug gaskets

    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, water pump impeller

    Check: spark plugs, fuel filter, thermostat, anodes

  3. Every 300 hours or 3 years

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

    Check: spark plugs, fuel filter, thermostat, anodes

  4. Every 400 hours

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

    Check: spark plugs, 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 75/90 FourStroke EFI service manual, 90-897725. 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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