MGB Oil Service & Filters Guide

Regular oil changes are the single most important maintenance task you can perform to keep your MGB running reliably. Fresh oil protects internal engine components, reduces wear and helps maintain proper operating temperatures. This guide covers everything you need to know about servicing the oil system on your MGB, from selecting the correct lubricant to replacing filters and identifying potential problems.

Understanding Your MGB's Lubrication System

The MGB's 1.8-litre B-Series engine uses a conventional wet sump lubrication system with a gear-type oil pump driven from the camshaft. Oil is drawn from the sump, pressurised by the pump, and distributed through internal galleries to the crankshaft bearings, camshaft, valve gear and other moving components. A relief valve maintains safe pressure regardless of engine speed.

Different model years use different oil filter configurations. Early cars (approximately 1962-1968) were fitted with canister-type Tecalemit or Purolator filters that accept replaceable paper elements. Later models received more convenient spin-on filters, either in an upright or hanging orientation, depending on the year. Understanding which type your car uses is essential when ordering replacement filters.

The MGB GT V8 uses the Rover V8 engine with its own distinct lubrication system and a remotely mounted spin-on filter. V8 owners should refer to V8-specific oil filter parts for correct component identification.

Choosing the Right Engine Oil

Selecting the appropriate oil for your MGB depends on the climate you drive in and the condition of your engine. The factory originally specified monograde oils, but modern multigrade alternatives offer improved cold-start protection and consistent viscosity across a wider temperature range.

For most MGB 4-cylinder engines in temperate climates, a quality 20W/50 mineral oil such as Castrol Classic provides excellent protection and is specifically formulated for older engine designs. This viscosity suits the bearing clearances and oil pump characteristics of the B-Series engine. In colder conditions or for engines rebuilt to tighter tolerances, 10W/40 semi-synthetic offers faster circulation at startup.

Avoid fully synthetic oils unless your engine has been rebuilt with modern seals throughout. The detergent packages in synthetic oils can cause leaks past older cork and rope seals. Check the MGB Engine Oil Chart for specific recommendations by model and year.

Model	Years	Oil Capacity (drain & refill)	Recommended Viscosity
MGB 4-cylinder	1962-1980	4.3 litres	20W/50 mineral
MGC	1967-1969	7.3 litres (with filter)	20W/50 mineral
MGB GT V8	1973-1976	5.1 litres	20W/50 mineral

Model

MGB 4-cylinder

Years

1962-1980

Oil Capacity (drain & refill)

4.3 litres

Recommended Viscosity

20W/50 mineral

Model

MGC

Years

1967-1969

Oil Capacity (drain & refill)

7.3 litres (with filter)

Recommended Viscosity

20W/50 mineral

Model

MGB GT V8

Years

1973-1976

Oil Capacity (drain & refill)

5.1 litres

Recommended Viscosity

20W/50 mineral

Oil Change Intervals

The original factory recommendation of 3,000 miles between changes remains sensible for MGBs in regular use. Modern oils offer improved longevity, but the fundamental engine design, potential blow-by past worn rings and lack of modern filtration efficiency mean that frequent changes remain beneficial.

Consider more frequent changes under the following conditions: short journeys where the engine rarely reaches full operating temperature, dusty or dirty environments, spirited driving with sustained high revs, or if you notice the oil darkening rapidly. Cars used occasionally or for long-distance touring in good conditions may extend intervals to 5,000 miles, though erring on the side of caution costs little and protects your engine.

Tools and Materials Required

Gather everything before you begin to make the job quick and clean. You will need a trolley jack and axle stands (or access to ramps), a drain pan capable of holding at least 5 litres, a suitable spanner for the sump plug (typically 3/4" or 19mm), and an oil filter removal tool appropriate to your filter type.

For 4-cylinder models with spin-on filters, a strap wrench or filter cup works well. Canister-type filters require only hand tools to remove the central bolt. Have fresh oil, a new filter, a new sump plug washer and clean rags ready before draining the old oil.

Step-by-Step Oil Change Procedure

1. Preparation: Warm the engine to operating temperature by driving for ten minutes or idling until the gauge reads normal. Warm oil flows more readily and carries contaminants in suspension, ensuring a more thorough drain. Position the car on level ground and engage the handbrake firmly.

2. Draining the Oil: Raise the front of the car and support it securely on axle stands. Never work beneath a vehicle supported only by a jack. Position your drain pan beneath the sump plug, which sits at the lowest point of the sump. Remove the plug and allow the oil to drain completely, which takes approximately fifteen minutes.

While the oil drains, inspect the plug and its washer. The magnetic sump plugs fitted to some models attract ferrous particles, so clean any accumulated debris. A small amount of fine metalite paste is normal; larger metal fragments warrant investigation. Replace the copper washer each time to ensure a leak-free seal.

3. Replacing the Filter: The filter location varies by model year. Spin-on types are accessed from beneath the car, while some canister types are more easily reached from above in the engine bay.

For spin-on filters, unscrew the old filter anticlockwise. Apply a thin film of fresh oil to the rubber seal of the new filter. Spin the filter on by hand until the seal contacts the mounting face, then tighten a further three-quarters of a turn by hand only. Over-tightening makes future removal difficult and can damage the seal.

For canister-type filters, remove the central bolt and withdraw the canister. Discard the old element and clean the inside of the canister thoroughly. Fit the new element, ensuring any seals are correctly positioned, and reassemble. Check that all sealing washers are present and in good condition.

4. Refilling with Fresh Oil: Refit the sump plug and torque to 25-30 lb-ft. Remove the oil filler cap on the rocker cover and pour in approximately 3.5 litres of fresh oil. Wait a minute for the oil to settle, then check the dipstick. Add oil gradually until the level sits between the minimum and maximum marks.

Start the engine and let it idle for thirty seconds while checking the oil pressure gauge. Pressure should rise immediately. Check beneath the car for any leaks at the sump plug and filter. Stop the engine, wait five minutes for oil to drain back to the sump, and recheck the level. Top up as necessary.

Understanding MGB Oil Filter Types

The MGB used several different filter arrangements throughout its production run, and identifying your specific configuration prevents ordering errors.

Canister Filters (1962-1969 approximately): Early cars used Tecalemit or Purolator canister filters mounted on the engine block. These accept replaceable paper cartridge elements. The canister itself is reused indefinitely unless damaged. Two orientations exist: hanging (suspended below the mounting boss) and upright (sitting above the mounting boss). Interchanging these requires different gaskets and sometimes additional parts.

Spin-On Filters (1969 onwards): Later production standardised on spin-on filters, which combine the element and housing in a single disposable unit. These are quicker to service but require the correct thread size and gasket diameter for your specific mounting head. Some owners convert earlier cars to spin-on filtration using adapter kits for convenience.

V8 Applications: The MGB GT V8 uses a remote-mounted spin-on filter on the inner wing, connected to the engine by oil lines. This differs significantly from 4-cylinder arrangements and requires V8-specific parts.

Oil Cooler Considerations

Many MGBs, particularly export models and those intended for warmer climates, were fitted with oil coolers as standard. The cooler sits in the airflow ahead of the radiator and helps maintain safe oil temperatures during demanding driving.

Check oil cooler hoses annually for deterioration, cracking or chafing. The rubber compounds degrade over time, and a failed hose can dump your oil supply in seconds. The cooler core itself should be inspected for damage from road debris and cleaned of accumulated dirt that reduces cooling efficiency.

Cars without factory oil coolers may benefit from retrofit cooler kits, particularly if used for spirited driving, towing or in hot climates. Thermostatically controlled systems prevent overcooling during warm-up. Browse our oil cooler components for available options.

Diagnosing Oil System Problems

When troubleshooting oil system issues, work methodically from the simplest and most likely causes through to more complex possibilities. This process of elimination approach saves time and prevents unnecessary repairs.

Low Oil Pressure

Understanding MGB Oil Filter Types

The MGB used several different filter arrangements throughout its production run, and identifying your specific configuration prevents ordering errors.

Symptom: Gauge reads below normal at idle or fails to rise adequately with engine speed. Normal hot idle pressure is 15-25 psi, rising to 50-70 psi at cruising speeds.

Diagnostic checklist (work through in order):

1. Check the oil level first. This is the most common cause of low pressure readings and the easiest to remedy. Top up if below the minimum dipstick mark and recheck pressure.

2. Verify the gauge is accurate. A faulty sender unit or corroded wiring gives misleading readings. Temporarily connect a mechanical gauge directly to the engine's oil gallery to confirm actual pressure before assuming internal engine problems.

3. Inspect oil condition. If the oil is excessively thin, contaminated or the wrong viscosity for your climate, pressure will suffer. Drain and refill with the correct grade.

4. Examine the pressure relief valve. A stuck-open valve bleeds pressure back to the sump. This component is externally accessible on most B-Series engines and can be removed, cleaned and tested without major disassembly.

5. Check the pickup strainer. A blocked strainer in the sump restricts flow to the pump. This requires sump removal but is straightforward to inspect and clean.

6. Assess oil pump condition. Worn pump gears and housing reduce pumping efficiency. Testing requires removal and measurement against service limits.

7. Investigate bearing wear. If all above checks prove satisfactory, worn main or big-end bearings are the likely cause. Excessive clearances allow oil to escape rather than build pressure. A temporary test involves switching to heavier oil (20W/60); if pressure improves noticeably, bearing wear is confirmed and engine work will be needed.

Oil Leaks

Symptom: Oil spots beneath the car, visible wetness around engine joints, or declining oil level between changes.

Diagnostic checklist (work through in order):

1. Clean the affected area thoroughly. Degrease the engine and surrounding components so you can observe fresh oil appearing. A dirty engine makes pinpointing leak sources impossible.

2. Check the sump plug and washer. The most common leak point after an oil change. Ensure the plug is correctly torqued and the copper washer is fresh and undamaged.

3. Inspect the oil filter and its seal. Spin-on filters can weep if the old rubber gasket remained stuck to the mounting face when the filter was changed. Canister filters leak if the sealing washers are missing or perished.

4. Examine the rocker cover gasket. Oil pooling on the exhaust manifold often originates here. The cork gasket compresses over time and loses its seal.

5. Check the timing cover seal. Oil appearing at the front of the engine below the timing cover indicates this seal has failed.

6. Inspect the rear crankshaft seal. Oil dripping from the bell housing area suggests rear main seal failure. This is more involved to replace but should be confirmed before committing to the repair.

7. Assess the sump gasket. Seepage along the sump-to-block joint indicates gasket deterioration. The entire sump must be removed to replace this gasket.

The engine gasket sets section offers replacement seals for all applications once you have identified the source.

Oil Consumption

Symptom: Oil level drops between changes, requiring top-ups. Blue exhaust smoke may be present.

Diagnostic checklist (work through in order):

1. Quantify the consumption rate. Some consumption is normal in older engines. Up to one pint per 1,000 miles is generally acceptable. Only consumption exceeding this warrants investigation.

2. Rule out external leaks first. Oil disappearing externally appears as leaks rather than consumption. Complete the leak diagnosis above before assuming internal causes.

3. Observe exhaust smoke colour and timing. Blue smoke on startup that clears indicates worn valve stem seals allowing oil past overnight. Blue smoke under acceleration suggests worn piston rings. Constant blue smoke points to significant bore wear.

4. Check the crankcase ventilation system. A blocked or malfunctioning breather can pressurise the crankcase, forcing oil past seals and into the combustion chambers.

5. Perform a compression test. Low compression on one or more cylinders, combined with oil consumption, confirms ring or bore wear requiring engine work.

6. Consider a leak-down test. This identifies whether compression loss occurs past the rings (into the crankcase) or past the valves, helping target repairs accurately.

Contaminated Oil

Symptom: Oil appears abnormal in colour or consistency when checked on the dipstick or drained.

Diagnostic checklist (work through in order):

1. Identify the contamination type. Milky, frothy oil indicates water or coolant mixing with the oil. Separate water droplets at the bottom of drained oil suggest condensation. Fuel-diluted oil smells of petrol and appears thinner than normal.

2. For condensation (water droplets): This results from short journeys where the engine never reaches full operating temperature. The remedy is simply to take the car for a longer run to evaporate moisture, then change the oil.

3. For coolant contamination (milky appearance): This is serious and requires immediate attention. Check the coolant level for corresponding loss. The most common cause is a blown head gasket allowing coolant into the oil galleries. A combustion leak test or chemical sniffer test of the coolant confirms head gasket failure. Do not continue running the engine, as coolant-contaminated oil loses its lubricating properties and causes rapid bearing wear.

4. For fuel contamination: A rich-running carburettor, faulty choke mechanism, or leaking fuel pump diaphragm can wash fuel past the rings into the sump. Diagnose and repair the fuel system fault, then change the oil.

Completing a Full Service

An oil change provides an ideal opportunity to address other routine maintenance items simultaneously. Service kits bundle the most commonly needed components for convenience, typically including oil filter, air filter elements, fuel filter, spark plugs and ignition points for cars with contact breaker ignition.

Replacing air filters at each oil change ensures the engine breathes clean air, protecting against premature bore wear. Check spark plug condition while servicing and replace if electrodes appear worn or deposits are heavy. Inspect all fluid levels, including coolant, brake fluid and gearbox oil.

DISCLAIMER: THIS GUIDE PROVIDES GENERAL INFORMATION FOR EDUCATIONAL PURPOSES. ALWAYS REFER TO THE OFFICIAL WORKSHOP MANUAL FOR YOUR SPECIFIC MODEL AND CONSULT A QUALIFIED MECHANIC IF YOU ARE UNCERTAIN ABOUT ANY PROCEDURE. RIMMER BROS ACCEPTS NO LIABILITY FOR WORK CARRIED OUT BASED ON THIS GUIDE. BRAKE SYSTEMS ARE SAFETY-CRITICAL, AND IMPROPER MAINTENANCE CAN RESULT IN SERIOUS INJURY OR DEATH.

Browse our full range of MGB parts and accessories

Frequently Asked Questions

What oil should I use in my classic MGB engine?

The ideal oil choice for your MGB depends on several factors, including engine condition, typical ambient temperatures, and your driving style. For most owners running an original or rebuilt engine with standard clearances, a quality 20W/50 mineral oil formulated for classic vehicles provides excellent protection and is precisely what these engines were designed to use. Castrol Classic 20W/50 and similar heritage-grade oils contain appropriate additive packages for flat-tappet camshafts, which require higher levels of zinc (ZDDP) than modern oils provide. Contemporary oils are formulated for modern engines with roller followers and catalytic converters, meaning their additive chemistry has evolved away from what older engines need. Using a dedicated classic car oil ensures your camshaft, tappets, and other high-load components receive adequate anti-wear protection. In colder climates where temperatures regularly drop below freezing, a 10W/40 semi-synthetic offers easier cold starting and faster oil circulation during the critical warm-up period. However, avoid fully synthetic oils unless your engine has been comprehensively rebuilt with modern seal materials throughout. The aggressive detergent packages in synthetic oils can cause leaks past older cork, rope, and felt seals, creating messy drips and potentially dangerous oil loss. For engines showing signs of wear, such as increased oil consumption or slightly low oil pressure, some owners find that a heavier 20W/60 oil helps maintain adequate pressure and reduces consumption. This should be considered a temporary measure rather than a permanent solution, as worn bearings and bores ultimately require mechanical attention rather than thicker oil.

How do I know which type of oil filter fits my MGB?

Identifying the correct oil filter for your MGB requires understanding the different filtration systems used across the model's production span. The changeover points between systems were not always tied to specific chassis numbers, and previous owners may have converted cars to different configurations, so visual inspection is the most reliable method. The earliest MGBs from 1962 used Tecalemit or Purolator canister-type filters. These feature a cylindrical metal housing bolted to a mounting boss on the engine block, with a replaceable paper element inside. Two orientations exist: hanging filters suspend below the mounting boss, while upright filters sit above it. The canister is removed by undoing a central bolt, the old element is discarded, and a new cartridge is inserted. If your car has this arrangement, you need paper element replacements rather than complete spin-on units. Around 1968, production transitioned to spin-on filters where the filter element and housing form a single disposable unit. These screw directly onto a threaded mounting head. Both upright and hanging orientations continued, with the distinction important for clearance in the engine bay. Spin-on filters are available in pattern aftermarket and original specification variants. Some owners convert canister-type systems to spin-on using adapter kits for convenience. If your car has been modified this way, check what adapter is fitted and order the matching spin-on filter. When in doubt, measure the thread size and gasket diameter, or photograph your existing filter setup and get in touch with our sales team who can identify the correct replacement from your images.

Why is my MGB losing oil pressure when the engine gets hot?

Declining oil pressure as the engine reaches operating temperature is one of the most common concerns MGB owners raise, and understanding the causes helps determine whether the situation requires urgent attention or simply monitoring. Oil naturally becomes thinner as it heats up, reducing viscosity and therefore the pressure the pump can generate against internal clearances. A modest drop from cold readings to hot is entirely normal. Typical healthy hot idle pressure sits between 15-25 psi, rising to 50-70 psi at cruising revs. If your readings fall within this range when hot, the system is functioning correctly. When hot idle pressure drops below 10 psi or fails to rise adequately with engine speed, investigation is warranted. The most common causes include worn main or big-end bearings, which allow oil to escape rather than build pressure. A simple check involves temporarily switching to a heavier oil, such as 20W/60. If pressure improves noticeably, bearing wear is likely the culprit, and engine work will eventually be needed. The oil pump itself can wear, though this is less common than bearing wear. The pump gears and housing develop clearances over time, reducing pumping efficiency. A failing pressure relief valve that sticks open also prevents proper pressure build-up. The pickup strainer in the sump can become blocked with sludge, restricting flow to the pump. Before assuming the worst, verify that your oil level is correct and that the pressure gauge itself is accurate. A faulty gauge sender unit or corroded connections can give misleading readings. Checking pressure with a mechanical gauge temporarily plumbed into the system confirms whether the problem lies with the engine or the instrumentation.

Can I convert my early MGB from a canister to a spin-on oil filtration?

Converting from a canister-type oil filter to modern spin-on filtration is a popular modification that simplifies oil changes and eliminates the need to source increasingly scarce paper cartridge elements. The conversion is straightforward and reversible, making it attractive for owners who want convenience without permanently altering their cars. Conversion kits replace the original canister mounting boss with a threaded head that accepts standard spin-on filters. The kits include all necessary gaskets, seals, and fittings. Installation involves draining the oil, removing the old canister assembly, fitting the new adapter head, and installing a spin-on filter. The whole process takes less than an hour with basic hand tools. The main consideration when converting is ensuring adequate clearance for the new filter position. Spin-on filters are generally larger than the paper elements they replace, and interference with exhaust manifolds, steering components, or chassis rails can occur depending on the specific kit and filter combination. Kits designed specifically for MGB applications account for these clearances, but generic adapters may present fitment challenges. Quality matters when selecting conversion components. The adapter head sees full oil system pressure and must seal reliably against the block mounting face. Poorly manufactured kits with inadequate machining or thin castings risk leaks or even catastrophic failure. Stick with reputable suppliers and proven kits rather than the cheapest available options. Browse our 4-cylinder oil filter options for compatible components, including conversion adapters and correct spin-on filters. Once converted, regular spin-on filters are widely available and inexpensive compared to sourcing the correct paper elements for original canister systems. Many owners consider this a sensible update that makes maintenance easier without affecting the car's character or authenticity in any meaningful way.

Chris Wrigley

Commercial Manager

Chris has been a car enthusiast since the early 1990’s and got his first Triumph Spitfire in 1996, one of many classics that followed!