What goes wrong, what it costs, and what to check before you buy a used MG MGB.
The MG MGB occupies a niche position on the UK market.
We track 5 known issues across the MG MGB range, including 1 rated as safety-critical. Knowing which variants and configurations to approach with caution can save you from expensive surprises after purchase.
Found a MG MGB? Enter the reg to see which of our 5 known issues apply to that exact car, plus full MOT history and mileage checks.
MkI (1962–1967) — Engine options included the B-Series 1.8. Our database flags 4 known issues on this generation, 1 of which are rated as safety-critical. The most significant concern is Extensive body corrosion (£500–£2,000 to address).
MkII (1967–1969) — Engine options included the B-Series 1.8. Our database flags 5 known issues on this generation, 1 of which are rated as safety-critical. The most significant concern is Extensive body corrosion (£500–£2,000 to address).
MkIII (1969–1974) — Engine options included the B-Series 1.8, B-Series 1.8. Our database flags 5 known issues on this generation, 1 of which are rated as safety-critical. The most significant concern is Extensive body corrosion (£500–£2,000 to address).
MkIV (1974–1980) — Engine options included the B-Series 1.8. Our database flags 5 known issues on this generation, 1 of which are rated as safety-critical. The most significant concern is Extensive body corrosion (£500–£2,000 to address).
The MGB monocoque construction uses thin steel panels that corrode extensively in the British climate. Critical structural areas include the sills (which form part of the chassis), floor pans, A-post bases, and rear spring hangers. Unlike modern cars with separate chassis, MGB structural integrity depends entirely on the shell remaining sound. Many examples have been poorly repaired with fibreglass or filler, masking serious structural weakness. Professional restoration costs often exceed the finished car's value.
Sill corrosion renders the car structurally unsound and dangerous to drive. Floor rust-through allows exhaust fumes into the cabin. Professional steel sill replacement costs £2,000-£5,000 plus paintwork. Many MGBs are written off rather than properly repaired due to the extent of hidden corrosion discovered once restoration begins.
Inspect the wheel arches, sills, jacking points and door bottoms carefully. Press gently on sills to check for soft spots. Look underneath for corrosion on structural components. Check the MOT history for corrosion-related advisories or failures.
The Laycock de Normanville Type A overdrive unit fitted to many MGBs operates hydraulically using engine oil pressure. The system includes solenoids, one-way clutches, and precision-machined components that wear over time. Electrical switch failure, worn solenoids, or internal clutch wear can prevent engagement or cause the unit to slip under load. Repair requires specialist knowledge and is expensive because the unit must be removed with the gearbox.
Complete overdrive failure leaves the car with a standard four-speed gearbox. Slipping overdrive makes motorway driving uncomfortable due to high engine speeds in fourth gear. Specialist rebuild costs £800-£1,500 plus removal and refitting. Some owners choose to live without overdrive rather than repair it.
Test the automatic gearbox extensively in slow traffic, car parks and on hill starts. Feel for any juddering, hesitation or clunking during gear changes. Try repeated low-speed manoeuvres as this is where problems are most apparent.
MGB electrical systems use Lucas components including the notorious positive-earth charging system (pre-1967) and various switches, relays, and wiring looms of variable quality. Common failures include indicator switches, headlight relays, charging system irregularities, and general wiring deterioration. The reputation for unreliability is partly historical but many surviving cars have modified or updated electrical systems that may not be properly documented.
Electrical failures can leave you stranded or create safety issues if lights fail at night. Most faults are repairable by any auto-electrician familiar with classic cars. Complete rewiring costs £500-£1,500 but dramatically improves reliability. The car remains drivable with most electrical faults.
Check all electrical functions systematically: windows, mirrors, lights, infotainment, heated seats, air conditioning. Look for any warning lights on the dashboard. A diagnostic scan before purchase can reveal stored fault codes.
All MGBs use twin SU carburettors (HS4 or HIF types depending on year) that require regular balancing to maintain smooth running. The carburettors have adjustable mixture screws, throttle synchronisation, and float chambers that can drift out of specification. Modern ethanol-blend petrol can affect rubber diaphragms and gaskets more than period fuel. Worn carburettors cause poor fuel economy, flat spots during acceleration, and rough idling.
Poor carburettor setup reduces performance and fuel economy but does not damage the engine. Professional balancing and tune costs £100-£200 and should restore smooth running. Complete carburettor rebuilds are needed every 20,000-30,000 miles depending on fuel quality and usage patterns.
Check for rough idle, hesitation or misfires during the test drive. Listen for the fuel pump priming when you turn the ignition on. Carbon buildup issues are more common on direct-injection engines — ask about intake cleaning history.
B-Series engines and associated transmissions commonly develop oil leaks from multiple sources including the rear main seal, timing cover, rocker cover gasket, and gearbox input shaft seal.
Excessive fluid leaks now fail MOT tests and must be repaired before the car can be legally driven. Multiple seal replacement can cost £300-£800 depending on accessibility. The car remains mechanically sound but may be refused MOT certification until leaks are reduced to acceptable levels.
Check the oil level before the engine is started. Ask the seller how often they top up the oil between services. After a test drive, check the level again and look behind the car for blue or grey exhaust smoke under acceleration.
For the full breakdown of all 5 tracked issues with repair costs, see the MG MGB common problems page.
Based on 2k real DVSA MOT tests, the MG MGB fails more often than average on several items. The biggest outlier is wheel bearings worn at 37x the fleet average, followed by fluid leak (17x).
When viewing a specific car, check its MOT history for recurring advisories in these categories. See the full MG MGB MOT failure breakdown for data at every mileage point.
Routine servicing (oil and filter change every 3k miles) typically costs £80–£120 at an independent garage.
See the full MG MGB service schedule for every interval and cost breakdown.
The MG MGB has some well-documented weak points, including 1 safety-critical issue that demand careful checking. The right example, properly maintained, can still be a sound purchase — but cutting corners on the pre-purchase inspection is not advisable.
Before committing, check the car's full MOT history, verify the service record is complete, and if possible arrange a specialist inspection. Enter any registration into our free report to see the complete picture.
Get Car Wise maintains a database of known mechanical issues for every popular car on UK roads, tracking the faults that owners, specialists and DVSA data reveal.
When you run a report on a specific MG MGB, we cross-reference the exact variant, engine and age against our database of 5 known issues. Combined with full MOT history analysis, mileage verification and DVLA data, you get a complete picture before viewing.
Enter the registration for MOT history, mileage verification, known faults for that exact variant, and a Get Car Wise Score.
This guide was compiled from independent expert reviews, DVSA MOT data, specialist workshops and our own database of 5 known MG MGB issues. We are not affiliated with any source listed.