Start with something the industry does not advertise: “interim”, “full” and “major” are trade conventions, not defined standards. Nobody is obliged to include any particular item in any of them. What matters is what is on the schedule, and whether the garage will tell you plainly what that is before they start.

That said, the conventions are reasonably consistent, and they exist for a sensible reason. Some jobs need doing twice as often as others, so bundling everything into one annual visit would mean either doing cheap work too rarely or expensive work too often.

What An Interim Service Covers

An interim — sometimes called a basic or intermediate service — is the short one, usually done between full services or annually on a car that does very few miles.

Typically it includes an engine oil and oil filter change, a check of all levels and top-ups where needed, a visual inspection of brakes, tyres, steering and suspension components, a look at the exhaust, belts and hoses, lights and wipers checked, and a general look over for leaks and anything obviously on its way out.

What it usually does not include is the other filters. Air, fuel and cabin filters normally sit on the full service list, and that is the main practical difference.

What A Full Service Adds

A full service does everything the interim does, plus the items that come round annually or at longer mileages. In broad terms:

• Air filter replaced
• Cabin or pollen filter replaced
• Fuel filter replaced where the schedule calls for it — common on diesels, less so on petrols
• Spark plugs on petrol cars, depending on the type fitted and the interval
• Brakes inspected more thoroughly, including measuring pad and disc wear rather than glancing at them
• Coolant strength and brake fluid condition tested, not just eyeballed
• A wider check of suspension, bushes, driveshaft gaiters, steering joints and exhaust mountings
• Road test, where the point is to feel for things a static check will never find

For most people running a normal car with normal mileage, this is the sensible default. We will say that straight rather than dress it up: unless your car covers very few miles or you know the last full service was recent, a full service once a year is the option that keeps on top of things without paying for work the car does not need yet.

What A Major Service Adds

A major service is a full service with the longer-interval items folded in. Which items those are depends entirely on the car, which is why a major service quoted without reference to your vehicle should make you ask questions. It commonly includes brake fluid renewal, coolant renewal, and depending on the schedule the gearbox oil, differential oil, or transmission fluid on an automatic.

Two things a major service is not: it is not a cambelt change, and it is not an MOT. Timing belts run to their own interval and are a separate job — an important one — and they get priced separately because the work involved varies enormously between engines. Some schedules do line the two up, which is worth knowing when you budget.

Intervals: Mileage And Time Both Count

Every manufacturer publishes an interval expressed two ways — a mileage figure and a time figure, whichever comes first. People remember the mileage and ignore the time, and that is exactly the wrong way round for a lot of cars now.

Oil does not only wear out from miles. It degrades from heat cycling, it gets diluted by fuel and contaminated by combustion by-products, and it collects moisture. On a car doing short trips the engine may barely reach full operating temperature, so the moisture never boils off and the oil ages faster per mile than it would on a car doing motorway runs. Acids build up in oil that is sitting in a cold engine, and those acids attack bearing surfaces whether you are driving or not.

So a car doing 3,000 miles a year still needs an annual oil change. Arguably it needs one more than the high-mileage car does, because those 3,000 miles were probably the hardest kind of use an engine gets. A car parked most of the week and used for a few short journeys is in the demanding category, not the easy one.

Choosing Based On How You Actually Use The Car

Forget the names for a minute and think about the driving:

• High mileage, mostly longer runs. Interim at the halfway point, full annually. You will hit the mileage trigger before the time one, so you will be servicing more than once a year.
• Average mileage, mixed driving. Full service annually. Major when the schedule’s longer-interval items fall due, typically every second or third year.
• Low mileage, short trips. Full service annually regardless of what the odometer says, and pay attention to brake fluid, coolant and corrosion — standing does more damage than driving here.
• Vans and anything that works for a living. Shorter intervals, more often. Load, idling and stop-start town work are hard on oil, brakes and clutches, and downtime costs more than servicing.
• Car that has stood for a long while. Treat it as needing a full service before you rely on it, whatever the last stamp says. Fluids, tyres and brakes all deteriorate standing still.

Why The Record Matters As Much As The Work

A service is worth having done properly and it is worth having written down. A clear history with dates, mileages, what was replaced and the parts used protects the car’s value, helps whoever works on it next, and matters if there is ever a warranty question. Loose receipts in the glovebox are better than nothing, but a proper record is better still.

If you are not sure what is due on your car, tell us the make, model and mileage and we will tell you what the schedule asks for and what we would actually do. Our servicing and repair work is carried out at your home or workplace, and where a job needs more than a mobile setup allows it gets booked in with us instead.