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General Motors MCM 3.0L / 3.0LX Engine

The General Motors MCM 3.0L / 3.0LX is a 3 L 4-cylinder engine. It powers generator sets from Mercury Marine, including the MCM 3.0L. It holds 3.8 L (1.0 gal) of oil and 3.8 L (1.0 gal) of coolant.

Also known as: General Motors (GM) MCM 3.0L / 3.0LX

3.0 L

Displacement

Cylinders

3.8 L

Oil capacity

On this pageSpecs Generator sets Maintenance FAQ Service intervals Torque & specs Fluids Procedures

Engine specifications

Oil capacity	3.8 L
Coolant capacity	3.8 L
Displacement	3.0 L
Cylinders	4

Generator sets powered by this engine

Mercury Marine MCM 3.0L

This engine also powers 2 machine(s) on Power Equipment Info.

Common problems

Wet Fouling (Oil Deposits)
Cause: Excessive oil entering combustion chamber, usually in engine with many hours of operation. Worn piston rings, cylinder walls, valve guides or valve stem seals are causes of oil entering combustion chamber.
Fix: Only engine repairs will permanently relieve oil wet fouling. New engines or recently overhauled engines may wet foul plugs before normal oil control is achieved with proper break-in procedures. Such fouled plugs may be serviced (clean, file and re-gap) and reinstalled.
Scavenger Deposits
Cause: Powdery white or yellow deposits are built up on shell, insulator and electrodes. This is normal appearance with certain branded fuels. Accumulation on ground electrodes and shell areas may be unusually heavy, but may be easily chipped off.
Fix: Plugs can be serviced (clean, file and re-gap) and reinstated.
Overheating
Cause: Insulator is dull white or gray and appears blistered. Electrodes are eroded and there is an absence of deposits. Check that correct plug heat range is being used. Also check for over-advanced ignition timing, cooling system malfunction, lean fuel/air mixtures, leaking intake manifold or sticking valves.
Fix: Replace spark plugs.
High Speed Glazing
Cause: Insulator has yellowish, varnish-like color, indicating that temperatures suddenly have risen, usually during hard, fast acceleration under heavy load. Normal deposits do not get a chance to blow off. Instead, they melt and form a conductive coating.
Fix: Replace plugs. If condition recurs, use colder heat range plug and service plugs more frequently.
Cold Fouling
Cause: Dry, black deposits indicate rich fuel mixture or weak ignition. Clogged flame arrestor, flooding carburetor, sticky choke or weak ignition components all are probable causes.
Fix: If only one or two plugs in set are fouled, check for sticking valves or bad ignition leads. After correcting cause, service (clean, file and re-gap) plugs and reinstall.
Chipped Insulator
Cause: Careless plug re-gapping. Severe detonation also can split insulator firing ends.
Fix: Plug must be replaced.

Compiled from service & troubleshooting documentation across every generator set that uses the General Motors MCM 3.0L / 3.0LX.

Maintenance schedule

Item	Capacity	Part #	Interval
Air filter		72420		Amazon eBay
Fuel filter		—	20 hr
Oil filter		50617	20 hr	Amazon eBay
Belt		72012		Amazon eBay
Coolant filter		—
Oil	4.0 U.S. Qts.	—	20 hr
Spark plug		—

Pooled from every document that names this exact engine — confirm the interval and part number against your unit's serial number.

Service intervals

Item	Action	Hours	Months	Notes
20-Hour checkup	Other	20 hr		First service — To be done by dealer
Propeller shaft	Lubricate	50 hr	2 mo	Saltwater: every 50 hours or 60 days; Freshwater: every 100 hours or 120 days
Shift, throttle cables and linkages	Lubricate	50 hr	2 mo	Saltwater: every 50 hours or 60 days; Freshwater: every 100 hours or once yearly
Crankcase oil and filter	Change	100 hr	12 mo	Every 100 hours or once yearly
Drive belts (all)	Inspect	100 hr	4 mo	Every 100 hours or 120 days, whichever occurs first; inspect condition and check tension
Engine alignment	Check	100 hr	12 mo	Every 100 hours or once yearly
Engine coupling, universal joint shaft splines	Lubricate	100 hr	12 mo	Every 100 hours or once yearly
Flame arrestor and crankcase ventilation hose	Clean	100 hr	12 mo	Every 100 hours or once yearly
Gimbal ring clamping screws	Adjust	100 hr	12 mo	Retorque to 40 lb. ft. (54 N-m); every 100 hours or once yearly
Ignition system	Clean	100 hr	12 mo	Clean and inspect condition
Stern drive unit oil	Change	100 hr	12 mo	Every 100 hours or once yearly
Transom gimbal housing assembly swivel shaft and gimbal bearing	Lubricate	100 hr	12 mo	Every 100 hours or once yearly
Continuity circuit	Check	200 hr	12 mo	Check components for loose connections, broken or frayed wires
Electrical system	Check	200 hr	12 mo	Check for loose or damaged wiring
Steering system	Lubricate	200 hr	12 mo	Lubricate and inspect for loose, damaged or missing parts
Universal joint cross bearings	Lubricate	200 hr	12 mo	Every 200 hours or once yearly
Closed cooling coolant	Replace		24 mo	Replace every two years
Closed cooling coolant	Test		12 mo	Test for alkalinity - once a year
Heat exchanger	Clean		12 mo	Clean seawater section - once a year
Power package exterior surfaces	Clean		12 mo	Clean and paint; spray with rust preventive - once a year
Quicksilver Mercathode system	Test		12 mo	Test output - once a year

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Service specifications

Type	Item	Value	Unit	Condition
Clearance	Camshaft End Play	.003-.008(0.08-0.2032) Max	in. (mm)
Clearance	Connecting Rod Side Clearance	.006-.014 (0.152-0.356)	in. (mm)
Clearance	Crankshaft End Play	.002-.006(0.05-0.15)	in. (mm)
Clearance	Main Bearing Clearance No.1-No.4	.001-.0025(0.03-0.06)	in. (mm)
Clearance	Pinion Clearance (Starter)	.010-.140 (0.25-3.5mm)	in. (mm)
Gap	Breaker Point Gap	.016 in. (0.5 mm)	in.
Gap	Spark Plug Gap	.035 In. (0.9 mm)	in.
Other	Breaker Point Spring Tension	20-27 oz. (567 - 765 g)	oz.
Other	Firing Order	1-3-4-2		L.H. Rotation
Other	Ignition Timing (Breaker Points Ignition)	8° BTDC	degrees	at Idle RPM
Other	Point Dwell	39° - 45°	degrees
Other	Timing (DDIS Ignition)	8° BTDC	degrees	at 700 RPM
Other	Timing (EST Ignition)	1° BTDC	degrees	at Idle RPM; must be set using special procedure
Pressure	Compression Pressure	140 PSI (966 kPa)	PSI
Pressure	Fuel (Pump) Pressure	5-1/4 - 6-1/4 PSI (36-44 kPa)	PSI	at 1800 RPM
Pressure	Min. Oil Pressure (at Idle)	5 - 6-1/2 PSI (35-44 kPa)	PSI	at Idle
Pressure	Oil Pressure (at 2000 RPM)	30-60 PSI (207-414 kPa)	PSI	at 2000 RPM
Speed	Idle RPM (in Forward Gear)	650-700	RPM
Speed	Maximum RPM (at W.O.T.)	4200-4600	RPM	MCM 3.0L
Speed	Maximum RPM (at W.O.T.)	4400-4800	RPM	MCM 3.0LX
Temperature	Thermostat	143°F (62° C)	°F
Torque	Camshaft Sprocket Bolts	80	lb. in.
Torque	Connecting Rod Cap Nuts	45 lb. ft. (61 N-m)	lb. ft.
Torque	Cylinder Head Bolts	90 lb. ft. (122 N-m)	lb. ft.	Retorque after first 20 hours of operation
Torque	Distributor Clamp	20 lb. ft. (27 N-m)	lb. ft.
Torque	Engine Coupler to Flywheel	35 lb. ft. (47 N-m)	lb. ft.
Torque	Flywheel Housing to Block	21 lb. ft. (28 N-m)	lb. ft.
Torque	Flywheel to Crankshaft Bolts	65 lb. ft. (88 N-m)	lb. ft.
Torque	Front Cover Bolts	30 lb. in. (3.4 N-m)	lb. in.
Torque	Front Engine Mounts	30-40 lb. ft. (42-54 N-m)	lb. ft.
Torque	Front Mount to Block	21 lb. ft. (28 N-m)	lb. ft.
Torque	Main Bearing Cap Bolts	65 lb. ft. (88 N-m)	lb. ft.
Torque	Manifold to Head	23 lb. ft. (31 N-m)	lb. ft.	Retorque after first start up
Torque	Oil Pan Bolts-Crankcase	80 lb. in. (9 N-m)	lb. in.
Torque	Oil Pan Bolts-to Front Cover	45 lb. in. (5 N-m)	lb. in.
Torque	Oil Pan Studs to Oil Seal Retainer or Crankcase	15 lb. in. (1.7 N-m)	lb. in.
Torque	Oil Pump Cover	72 lb. in. (8 N-m)	lb. in.
Torque	Oil Pump Pickup	60 lb. in. (7 N-m)	lb. in.
Torque	Oil Pump to Block	120 lb. in. (14 N-m)	lb. in.
Torque	Power Steering Hydraulic Hose Fittings	20-25 lb. ft. (27-34 N-m)	lb. ft.
Torque	Rear Crankshaft Oil Seal Retainer Nuts	135 lb. in. (15 N-m)	lb. in.
Torque	Rear Engine Mounts	35-40 lb. ft. (47-54 N-m)	lb. ft.
Torque	Rocker Arm Cover and Bolts	40 lb. in. (4.5 N-m)	lb. in.
Torque	Rocker Arm Nuts	20 lb. ft. (27 N-m)	lb. ft.
Torque	Spark Plugs	22 lb. in. (30 N-m)	lb. in.
Torque	Starter Motor to Block	37 lb. ft. (50 N-m)	lb. ft.
Torque	Thermostat Cover Bolts	30 lb. ft. (41 N-m)	lb. ft.
Torque	Timing Gear Cover	72 lb. in. (8 N-m)	lb. in.
Torque	Torsional Damper Bolt	50 lb. ft. (68 N-m)	lb. ft.
Torque	Water Pump to Block	15 lb. ft. (20 N-m)	lb. ft.
Valve clearance	Collapsed Tappet Gap	3/4 Turn Down from Zero Lash	turn	hydraulic lifters

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Recommended fluids

Fluid	Grade	Standard	Capacity	Notes
Coolant	Quicksilver Pre-Mixed Engine Coolant; or rust inhibitor and water mixed to manufacturer's recommendations		9.0 U.S. Qts. (8.5 L)	Closed cooling system (MCM Stern Drive). Alcohol or Methanol base antifreeze or plain water not recommended. Ethylene glycol antifreeze and water for storage; DO NOT use propylene glycol in closed cooling section
Engine oil	Quicksilver 4-Cycle Marine Engine Oil; or good grade straight weight detergent automotive oil of correct viscosity; 20W-40 (SF or SG), or second choice 20W-50 (SF or SG)	API classification SF or SG	4.0 U.S. Qts. (3.8 L)	Non-detergent oils, other multi-viscosity oils, low quality oils or oils with solid additives not recommended; always use dipstick for exact quantity
Fuel	Posted pump Octane Rating of 87 (R + M)/2 minimum (USA and Canada); 90 RON minimum (outside USA and Canada); Premium 92 (R + M)/2 and 98 RON also acceptable			DO NOT use leaded gasoline (USA/Canada). Fuel system withstands up to 10% alcohol content
Grease	Quicksilver 2-4-C Marine Lubricant with Teflon; Quicksilver Engine Coupler Spline Grease (92-816391A4); SAE 30W motor oil for pivot points			Cable guide contact surfaces with 2-4-C; coupler and splines with Engine Coupler Spline Grease
Hydraulic oil	Quicksilver Power Trim and Steering Fluid or automatic transmission fluid (ATF), Dexron III	Dexron III		Power steering system

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Procedures

Estimating Ignition Timing (Breaker Points) adjustment

⚠ Do not touch or disconnect any ignition system parts while engine is running

Tools: Timing Light 91-99379, Tachometer

Connect timing light to No. 1 spark plug; connect power leads to 12 volt battery.
Connect tachometer to engine.
Start engine and run at normal idle speed.
Aim timing light at timing tab on timing gear cover and crankshaft torsional damper.
Loosen distributor clamp and rotate distributor body until timing mark lines up with specified mark.
Tighten clamp and recheck location of timing mark.
Stop engine and remove timing light.

Valve Adjustment - Engine Not Running adjustment

Crank engine until mark on torsional damper lines up with center 0 mark on timing tab, engine in No. 1 firing position.
Adjust No. 1 cylinder exhaust and intake, No. 2 intake, No. 3 exhaust, No. 4 intake.
Back out adjusting nut until lash is felt at push rod, then turn in until all lash is removed.
Tighten adjustment nut an additional 3/4-turn.
Crank engine one revolution until pointer 0 and damper mark align (No. 4 firing position).
Adjust No. 2 exhaust, No. 3 intake, No. 4 exhaust.
Install distributor cap, spark plug wires and coil lead.
Install rocker arm cover; torque to 40 lb. in. (4.5 N-m).

Valve Adjustment - Engine Running adjustment

⚠ Preload adjustment must be done slowly to allow lifter to adjust itself, preventing valve contacting piston

Run engine until normal operating temperature, then remove valve cover.
With engine at idle, back off rocker arm nut until rocker arm starts to clatter.
Turn nut down slowly until clatter just stops (zero lash).
Turn nut down 1/4 additional turn and pause 10 seconds until engine runs smoothly.
Repeat additional 1/4 turns, pausing 10 seconds each, until nut has been turned down 3/4 turn from zero lash.
Repeat to adjust other valves.
Install valve covers, torque screws to 40 lb. in. (4.5 N-m).

Changing Oil and Filter maintenance

Tools: Quicksilver Crankcase Oil Pump

Start engine and run until it reaches normal operating temperature.
Stop engine.
Remove drain plug from oil pan or oil drain hose.
After oil drains completely, reinstall drain plug and tighten securely.
Remove and discard oil filter and sealing ring.
Coat sealing ring of new filter with engine oil and install; tighten securely, do not over-tighten.
Fill crankcase with oil.
Start engine and check for leaks.

Checking Engine Oil Level/Filling maintenance

⚠ Overfilled crankcase can cause oil pressure drop and rocker arm clatter

Allow oil to drain back into oil pan approximately 5 minutes.
Remove dipstick, wipe clean and reinstall fully into dipstick tube.
Remove dipstick and note oil level; must be between FULL and ADD marks.
If below ADD, remove oil filler cap from valve rocker arm cover.
Add oil to bring level up to but not over FULL mark.

Draining Seawater (Raw-Water) Cooled Models maintenance

⚠ Seawater section of cooling system MUST BE COMPLETELY drained for winter storage

⚠ DO NOT ALLOW ENGINE TO START when purging

Tools: Stiff wire

Ensure engine is as level as possible for complete draining.
Remove drain plugs from cylinder block and manifold.
Repeatedly clean out drain holes using a stiff piece of wire until entire system is drained.
Remove and lower hoses to allow them to drain.
Remove power steering fluid cooler seawater hose.
Insert a small wire repeatedly to make sure vent holes and water drain holes and passages are open.
Crank engine over SLIGHTLY with starter motor to purge water trapped in seawater pickup pump (DO NOT ALLOW ENGINE TO START).
Coat threads of drain plugs with Quicksilver Perfect Seal and reinstall; tighten securely and reconnect hoses.

Filling and Bleeding Power Steering System maintenance

⚠ DO NOT operate engine without water supplied to seawater pickup pump or pump impeller may be damaged

With engine stopped, position drive unit straight back and remove fill cap/dipstick.
Add fluid to bring level up to FULL COLD mark.
Turn steering wheel back and forth to end of travel each direction several times, recheck level and add fluid if necessary.
Install vented fill cap.
Start engine and run at fast idle (1000-1500 RPM) until normal operating temperature, turning steering wheel end-to-end several times.
Position drive unit straight back, stop engine, remove fill cap, allow foam to disperse, check level and add fluid to FULL HOT mark. Reinstall cap.
Repeat if fluid is still foamy.

Flushing Cooling System maintenance

⚠ Do not run engine above 1500 RPM when flushing

⚠ Be certain area in vicinity of propeller is clear

⚠ Watch temperature gauge to ensure engine does not overheat

Tools: Quicksilver Flushing Attachment, Garden Hose

Install Quicksilver Flushing Attachment over water intake openings in gear housing.
Connect hose between flushing attachment and water tap.
Partially open water tap (about 1/2 maximum capacity) and allow system to fill completely.
Place remote control lever in NEUTRAL and start engine.
Operate engine at idle in NEUTRAL for 10 minutes or until discharge water is clear, then stop engine.
Shut off water tap.
Remove hose and flushing attachment.

Layup (Cold Weather / Extended Storage) maintenance

⚠ Be careful working on fuel system; gasoline is extremely flammable

⚠ Be sure engine compartment is well ventilated and no gasoline vapors present

⚠ Stern drive unit should be stored in full down position

Fill fuel tanks with fresh gasoline without alcohol and Quicksilver Gasoline Stabilizer.
Replace all fuel filters.
Start engine and check for fuel leaks.
Run engine to normal operating temperature; shut off and change oil and filter.
Flush cooling system if operated in salty, polluted or mineral-laden water.
Remove flame arrestor and, at fast idle (1000-1500 RPM), fog induction system with about 8 ounces of Quicksilver Storage Seal or SAE 20W engine oil; stall engine with last 2 ounces.
Close fuel shutoff valve if equipped.
Clean flame arrestor and crankcase ventilation hoses and reinstall.
Lubricate all items outlined in Lubrication.
Drain seawater section of cooling system.
Test closed cooling coolant to withstand lowest expected temperature.
Service batteries.
Clean outside of engine and repaint; spray with corrosion and rust preventive.

Maintaining Closed Cooling Coolant Level maintenance

⚠ Allow engine to cool down before removing pressure cap; sudden loss of pressure could cause hot coolant to discharge violently

Allow engine to cool before removing pressure cap.
Turn cap 1/4 turn to allow pressure to escape slowly, then push down and turn off.
Coolant level in heat exchanger should be full (to bottom of filler neck).
Coolant level should be between ADD and FULL marks on coolant recovery reservoir with engine at normal operating temperature.
Reinstall pressure cap until it contacts stop on filler neck.

Priming Engines with Oil maintenance

⚠ Crank engine for 15 seconds, then allow starter motor to cool for 1 minute

Tools: 91-52024A1 Remote Starter Switch

Fill crankcase to proper level with recommended engine oil.
Remove spark plugs.
Leave ignition key in OFF position.
Connect remote starter switch to large 12V terminal (RED battery cable) and small terminal on starter motor.
Crank engine for 15 seconds, then allow starter motor to cool 1 minute.
Repeat until a total of 45 seconds of crank time is achieved.
Remove remote starter switch.
Install spark plugs and wires.
With cooling water supplied to seawater pump, start engine.

Water Separating Fuel Filter Replacement maintenance

⚠ Always disconnect battery cables BEFORE working on fuel system to prevent fire or explosion

Tools: Filter Wrench

Disconnect battery cables from battery.
Remove fuel filter from base; a filter wrench may be needed to loosen element.
Lubricate sealing ring(s) of new filter with SAE engine oil.
Install new filter, tightening securely by hand.
Reconnect battery cables, ensure water is supplied to cooling system and start engine.
Check for fuel leaks.

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Common questions

What is the oil capacity of the General Motors MCM 3.0L / 3.0LX?

The General Motors MCM 3.0L / 3.0LX engine has an oil capacity of 3.8 liters.

What is the displacement of the General Motors MCM 3.0L / 3.0LX?

The General Motors MCM 3.0L / 3.0LX has a displacement of 3.0 liters with 4 cylinders.

Which generators use the General Motors MCM 3.0L / 3.0LX engine?

The General Motors MCM 3.0L / 3.0LX powers 1 generator set(s), including Mercury Marine MCM 3.0L.

How often should you change the oil in the General Motors MCM 3.0L / 3.0LX?

The General Motors MCM 3.0L / 3.0LX oil change interval is every 20 hours.

What is a common problem with the General Motors MCM 3.0L / 3.0LX engine?

A commonly reported issue on generators using the General Motors MCM 3.0L / 3.0LX is: Wet Fouling (Oil Deposits). Cause: Excessive oil entering combustion chamber, usually in engine with many hours of operation. Worn piston rings, cylinder walls, valve guides or valve stem seals are causes of oil entering combustion chamber.. Fix: Only engine repairs will permanently relieve oil wet fouling. New engines or recently overhauled engines may wet foul plugs before normal oil control is achieved with proper break-in procedures. Such fouled plugs may be serviced (clean, file and re-gap) and reinstalled..