How often should engine oil be changed?

Engine oil should be changed every 5,000–10,000 miles or once a year — whichever comes first. Cars with older engines or high mileage should use the 5,000-mile interval. Check the owner's handbook for the manufacturer's recommended interval for your specific car.

What happens if you don't change engine oil?

Old engine oil loses viscosity and accumulates contaminants, reducing lubrication. This causes accelerated wear on bearings, camshafts, and turbochargers. Over time, sludge builds up and can block oil channels, leading to catastrophic engine failure costing £2,000–£5,000+.

What oil grade should I use for my car?

Use the grade specified in your owner's handbook — typically 5W-30 or 5W-40 for UK cars. Using the wrong grade can reduce protection. Turbocharged engines and modern direct-injection engines typically require a specific low-SAPS or full-synthetic oil. Do not substitute grades.

How do I check engine oil level?

With the engine cold and parked on level ground, pull out the dipstick, wipe it clean, reinsert it fully, then pull it out again. The oil level should be between the MIN and MAX marks. If below MIN, add oil in small increments. Check the colour — black and gritty means an overdue oil change.

Engine Oil and Servicing

What Does Engine Oil Do?

Lubrication: Reduces friction between moving engine parts
Cooling: Absorbs and dissipates heat away from the engine
Cleaning: Suspends dirt and sludge, keeping the engine clean
Protection: Forms protective barriers against corrosion and wear

Synthetic vs Mineral Oil

Mineral Oil

Refined from crude oil. Lower cost, standard for older cars. Thinner at high temperatures, breaks down faster, needs changing more frequently.

Service interval: Every 5,000–6,000 miles or 6 months (whichever comes first).

Semi-Synthetic Oil

Blend of mineral and synthetic. Better performance than mineral, cheaper than full synthetic. Good all-rounder.

Service interval: Every 10,000 miles or 12 months.

Fully Synthetic Oil

Man-made molecules, superior performance. Stays stable at extreme temperatures, lasts longer, reduces sludge. Higher cost but fewer oil changes needed.

Service interval: Every 15,000–20,000 miles or 12–24 months.

Understanding Oil Grades (e.g., 5W-40)

Oil grades describe viscosity (thickness) at different temperatures. "5W-40" means:

5W: Viscosity at winter temperatures (cold start). Lower numbers are thinner, easier to flow when cold
40: Viscosity at hot engine temperatures (100°C). Higher numbers are thicker, better for protection at heat

Always use the grade recommended in your car's handbook. Using the wrong grade affects performance and fuel economy.

What's Included in a Service?

Basic service (oil change): Oil and filter change. Cost: £50–£150.

Interim service: Oil change + filter change + fluid top-ups (coolant, brake fluid, washer fluid). Cost: £100–£200.

Full service: Oil change + filter + all fluid checks + brake pads inspection + air filter check + spark plugs (older cars). Cost: £200–£400.

How to Check Your Car's Oil Level

1. Park on level ground. Oil readings are inaccurate on slopes.

2. Let the engine cool for 5 minutes after switching off (oil needs time to drain back into the sump).

3. Locate the dipstick. Pull it out fully and wipe it clean.

4. Reinsert fully and pull out again. The oil should coat the stick up to the maximum mark. If below minimum, top up.

5. Check the oil color. Fresh oil is amber/translucent. Black oil means it is due for changing. Brown oil with sludge indicates poor maintenance.

Common Oil Problems

Low Oil Level

Indicates oil leaks or oil burning (damaged piston rings/seals). Top up immediately and get a mechanic to check the source.

Engine Sludge

Thick, black, sticky oil caused by poor servicing history. Sludge restricts oil flow and damages bearings. Indicates years of neglect.

Oil Light On Dashboard

Means oil pressure is low. Could be low oil level or faulty sensor. Check oil first; if level is fine, get the sensor checked.

When Buying a Used Car

Check the oil: Open the oil filler cap and look inside with a torch. Clean, translucent oil = good maintenance. Black sludge = neglected car.

Check service history: Gaps longer than 12 months between services indicate neglect. Consistent servicing means the engine is well-maintained.

Check the free MOT history to verify a car has been consistently maintained. Mileage recorded at each MOT test lets you cross-reference against claimed service intervals.

Engine Oil and Servicing Explained — What You Need to Know