Few engines are as important to Holden’s history as the legendary 186 Red Motor. Introduced in 1968, the 186 quickly became one of Holden’s most respected powerplants, finding its way into everything from HR and HK Holdens through to Monaros, Kingswoods, commercials and countless race and performance cars. With its simple pushrod design, impressive torque and exceptional durability, the 186 earned a reputation as one of Australia’s toughest six-cylinder engines.
Even today, many Holden enthusiasts consider the 186 the sweet spot of the Red Motor family. It offered noticeably stronger performance than the 149 and 161 while retaining excellent reliability and relatively low running costs.
However, no engine is perfect. Most surviving 186 engines are now more than fifty years old, and age-related wear has become the biggest source of problems. Oil leaks, cooling issues, worn timing gears and ignition faults are among the most common complaints faced by owners today.
Why the Holden 186 Became So Popular
Before looking at the problems, it’s worth understanding why the 186 remains so highly regarded.
Key Features
- Cast iron block
- Cast iron cylinder head
- Seven main bearing crankshaft
- Pushrod valve train
- Single-barrel Stromberg carburettor
- Excellent torque characteristics
The seven-bearing bottom end contributed significantly to the engine’s durability.
Many well-maintained 186 engines have exceeded 300,000 kilometres without major internal repairs.
Oil Leaks
The most common issue affecting Holden 186 engines is oil leakage.
Symptoms
- Oil spots on driveway
- Oil-covered engine bay
- Burning oil smell
- Gradual oil loss
Common Leak Locations
- Rocker cover gasket
- Side plate covers
- Timing cover
- Rear main seal
- Sump gasket
Most oil leaks are caused by ageing gaskets rather than major engine damage.
Best Oil Leak Repair Product
Recommended Product: Permaseal Engine Gasket Kit
Benefits
- High-quality sealing materials
- Direct fitment
- Comprehensive coverage
Best For
- Oil leak repairs
- Engine rebuilds
- Preventative maintenance
Replacing ageing gaskets often transforms a messy engine.
Timing Gear Failure
One of the best-known weaknesses of the Holden Red Motor family involves the factory timing gear.
Symptoms
- Engine misfire
- Poor performance
- Timing instability
- Difficulty starting
Why It Happens
Holden originally fitted a fibre camshaft timing gear.
Over time, the teeth become brittle and eventually fail.
In severe cases, the engine may stop running completely.
Cooling System Problems
Cooling issues are common in older 186-powered Holdens.
Symptoms
- Overheating
- Coolant loss
- Steam from radiator
- Rising temperature gauge
Common Causes
- Blocked radiator
- Worn water pump
- Faulty thermostat
- Internal corrosion
Many engines have accumulated decades of sediment inside the cooling passages.
Best Cooling System Upgrade
Recommended Product: Dayco Water Pump
Benefits
- Improved coolant circulation
- Reliable construction
- Direct replacement
Best For
- Cooling system rebuilds
- Preventative maintenance
- Touring vehicles
Worn Valve Guides
High-mileage 186 engines frequently develop valve guide wear.
Symptoms
- Blue smoke on startup
- Increased oil consumption
- Fouled spark plugs
- Reduced performance
Why It Happens
Thousands of operating hours gradually wear guide surfaces.
Valve guide wear is especially common on engines that have seen infrequent maintenance.
Excessive Oil Consumption
Not all oil consumption is caused by leaks.
Symptoms
- Frequent top-ups
- Blue exhaust smoke
- Carbon deposits
Common Causes
- Worn piston rings
- Valve guide wear
- Cylinder bore wear
Engines with significant oil consumption may require rebuilding.
Carburettor Problems
Most Holden 186 engines were fitted with a Stromberg carburettor.
Symptoms
- Rough idle
- Hesitation
- Poor fuel economy
- Hard starting
Common Causes
- Blocked jets
- Worn throttle shafts
- Dried gaskets
- Float issues
Fortunately, Stromberg carburettors are simple to rebuild.
Best Carburettor Rebuild Kit
Recommended Product: Stromberg Rebuild Kit
Benefits
- Restores fuel delivery
- Improves starting
- Better fuel economy
Best For
- Original restorations
- Routine maintenance
Ignition Problems
The original points ignition system requires regular maintenance.
Symptoms
- Hard starting
- Misfiring
- Rough idle
- Reduced performance
Common Causes
- Worn points
- Condenser failure
- Coil problems
- Distributor wear
Many drivability complaints can be traced directly to ignition issues.
Best Ignition Upgrade
Recommended Product: PerTronix Electronic Ignition Kit
Benefits
- Eliminates points wear
- Improved reliability
- Better starting
- Reduced maintenance
Best For
- Daily drivers
- Touring vehicles
- Mild performance upgrades
This is one of the most popular upgrades among Red Motor enthusiasts.
Rear Main Seal Leaks
The rear main seal is notorious among Holden owners.
Symptoms
- Oil dripping from bellhousing
- Persistent oil leaks
- Dirty transmission housing
Why It Happens
The original rope-style seal design is effective when new but often leaks as components age.
Repairing rear main leaks usually requires transmission removal.
Fuel Pump Failure
Mechanical fuel pumps eventually wear out.
Symptoms
- Hard starting
- Fuel starvation
- Poor performance
- Stalling
Common Causes
- Diaphragm failure
- Internal wear
- Age-related deterioration
Best Fuel Pump Replacement
Recommended Product: Fuelmiser Mechanical Fuel Pump
Benefits
- Direct replacement
- Reliable fuel delivery
- Quality construction
Best For
- Restorations
- Daily drivers
- Touring Holdens
Oil Pressure Problems
Low oil pressure should never be ignored.
Symptoms
- Warning light activation
- Engine noise
- Bearing knock
Common Causes
- Worn oil pump
- Bearing wear
- Excessive engine wear
Regular oil changes are critical for maintaining oil pressure.
Best Engine Oil for Holden 186
Recommended Product: Penrite HPR 30
Benefits
- Suitable zinc levels
- Excellent wear protection
- Designed for older engines
Best For
- Standard 186 engines
- Rebuilt engines
- Classic Holdens
Penrite oils are widely used throughout Australia’s classic car community.
Common 186 Engine Repair Mistakes
Ignoring Cooling System Maintenance
Many overheating problems begin with neglected cooling systems.
Delaying Timing Gear Replacement
Factory fibre gears eventually fail.
Replacing them proactively can prevent breakdowns.
Using Modern Low-Zinc Oils
Older flat-tappet camshafts require suitable oil formulations.
Overlooking Ignition Maintenance
Points systems require regular adjustment and servicing.
The Holden 186 is rightly regarded as one of Australia’s greatest engines. Its combination of simplicity, durability and strong performance helped cement Holden’s reputation throughout the late 1960s and early 1970s. Most issues seen today are not design flaws but the result of decades of service and normal wear.
Oil leaks, timing gear failures, cooling system issues and ignition problems remain the most common concerns, but fortunately they are well understood and relatively easy to address. Products such as steel timing gears, PerTronix ignition kits, Penrite HPR 30 oil, Dayco water pumps and quality gasket kits can dramatically improve reliability and drivability.
For enthusiasts restoring an HR, HK, HT or HG Holden, understanding these common issues is the key to enjoying everything the legendary 186 Red Motor has to offer.
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