How much oil does a Mercury 5 HP LPG FourStroke take?

Approximately 450 ml (15 fl oz); No oil filter. Level is read on the oil filler cap dipstick with the outboard upright; from the add mark add 100 ml (3 oz).

What engine oil does a Mercury 5 HP LPG FourStroke use?

Mercury or Quicksilver NMMA FC-W certified 10W-30 4-Stroke Outboard Oil for all temperatures; NMMA FC-W certified synthetic blend 25W-40 may be used above 4 °C (40 °F).

What gear oil does a Mercury 5 HP LPG FourStroke use, and how much?

Mercury or Quicksilver Premium or High Performance Gear Lubricant. Quantity: Approximately 195 ml (6.6 fl oz). Fill until lubricant appears at the vent hole.

What spark plug does a Mercury 5 HP LPG FourStroke use?

Use the one on the engine’s emission decal. Qty 1. Gap: 0.9 mm (0.035 in).

How often should a Mercury 5 HP LPG FourStroke be serviced?

The factory schedule lists: Every 100 hours of use or once yearly, whichever occurs first; Every 300 hours of use or every 3 years, whichever occurs first; Every 500 hours of use or every 5 years, whichever occurs first. 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 5 HP LPG 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 propeller nut torque on a Mercury 5 HP LPG FourStroke?

17 Nm (150 lb-in), then secure the nut with a cotter pin.

Mercury 5 HP LPG (propane) FourStroke (1 cylinder 123 cc) service guide

Oil, gear oil, spark plugs and the service schedule for the Mercury 5 HP LPG (propane) FourStroke (1 cylinder 123 cc) (5 hp, four-stroke), from the factory service manual, plus how we service it in Hawaiʻi.

Models covered: Mercury 5 HP LPG (propane) outboard. 1 cylinder, 123 cc (7.51 cid), fueled by propane (liquified petroleum gas) through a mixer, no gasoline carburetor, no oil filter. Gear ratio 2.15:1.

Quick answers

How much oil does a Mercury 5 HP LPG FourStroke take?: Approximately 450 ml (15 fl oz); No oil filter. Level is read on the oil filler cap dipstick with the outboard upright; from the add mark add 100 ml (3 oz).
What engine oil does a Mercury 5 HP LPG FourStroke use?: Mercury or Quicksilver NMMA FC-W certified 10W-30 4-Stroke Outboard Oil for all temperatures; NMMA FC-W certified synthetic blend 25W-40 may be used above 4 °C (40 °F).
What gear oil does a Mercury 5 HP LPG FourStroke use, and how much?: Mercury or Quicksilver Premium or High Performance Gear Lubricant. Quantity: Approximately 195 ml (6.6 fl oz). Fill until lubricant appears at the vent hole.
What spark plug does a Mercury 5 HP LPG FourStroke use?: Use the one on the engine’s emission decal. Qty 1. Gap: 0.9 mm (0.035 in).
How often should a Mercury 5 HP LPG FourStroke be serviced?: The factory schedule lists: Every 100 hours of use or once yearly, whichever occurs first; Every 300 hours of use or every 3 years, whichever occurs first; Every 500 hours of use or every 5 years, whichever occurs first. 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 5 HP LPG 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 propeller nut torque on a Mercury 5 HP LPG FourStroke?: 17 Nm (150 lb-in), then secure the nut with a cotter pin.

Maintenance specs

Engine oil	Mercury or Quicksilver NMMA FC-W certified 10W-30 4-Stroke Outboard Oil for all temperatures; NMMA FC-W certified synthetic blend 25W-40 may be used above 4 °C (40 °F)
Engine oil quantity	Approximately 450 ml (15 fl oz); No oil filter. Level is read on the oil filler cap dipstick with the outboard upright; from the add mark add 100 ml (3 oz)
Engine oil drain bolt	20 Nm (177 lb-in), with washer; lubricate the seal on the drain plug with oil
Gear lube	Mercury or Quicksilver Premium or High Performance Gear Lubricant
Gear lube quantity	Approximately 195 ml (6.6 fl oz). Fill until lubricant appears at the vent hole
Gear lube fill/drain and vent plugs	1 fill/drain plug and 1 vent plug, each with a sealing washer; the gear housing section says to install new gaskets on the fill and vent plugs.
Spark plug	Use the one on the engine’s emission decal. Qty 1
Spark plug gap	0.9 mm (0.035 in)
Spark plug torque	27 Nm (20 lb-ft); or finger tight then 1/4 turn
Thermostat	Starts to open at 50 ± 1.5 °C (122 ± 3 °F); full open 63 ± 1.5 °C (145 ± 3 °F); valve lift 3 mm (0.12 in)
Anodes	One zinc anode on the gear case, retaining bolt 8 Nm (71 lb-in). Replace it if more than 50% is consumed
Propeller nut	17 Nm (150 lb-in), then secure the nut with a cotter pin
Valve clearance, cold	Intake 0.06 to 0.14 mm (0.002 to 0.005 in); exhaust 0.11 to 0.19 mm (0.004 to 0.007 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.

Every 100 hours of use or once yearly, whichever occurs first

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

Check: anodes
Every 200 hours or 1 year (our Hawai‘i yearly service) Hawai‘i

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

Check: spark plugs, anodes
Every 300 hours of use or every 3 years, whichever occurs first

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

Check: spark plugs, anodes
Every 500 hours of use or every 5 years, whichever occurs first

Replace: engine oil, oil drain plug gasket, 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 5 HP LPG Outboard service manual, 90-8M0156927. Specs can change by model year and serial number, so always confirm your exact model from the serial tag on the clamp bracket.

Mercury 5 HP LPG (propane) FourStroke (1 cylinder 123 cc) service guide

Quick answers

Maintenance specs

Service schedule

Every 100 hours of use or once yearly, whichever occurs first

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

Every 300 hours of use or every 3 years, whichever occurs first

Every 500 hours of use or every 5 years, whichever occurs first

Other Mercury guides