Servicing
Why a Car That Barely Moves Costs More to Keep
Brake fluid saturates in about two years, tyres age out by ten, and the service schedule runs on the calendar. A car doing 1,200 miles a year pays for all of it.
The assumption behind buying a low mileage car is that low use means low cost. Per mile it does not, and per year it barely helps at all. Brake fluid saturates on a clock rather than an odometer, tyres are written off by age with tread still on them, service intervals are worded as whichever comes first, and none of those clocks stop when the car is parked. A car covering 1,200 miles a year pays close to the same annual bill as one covering twelve times that, and every one of those miles carries the whole cost.
Brake fluid ages chemically, not mechanically
Brake fluid to DOT 4 is hygroscopic. It draws water out of the air through the microscopic porosity of rubber hoses and through the reservoir cap, and it does this whether the car is driven, parked or on a lift. Water lowers the boiling point, and the boiling point is the whole reason the fluid is there.
The specification is written around exactly this. A DOT 4 fluid must have a dry boiling point of at least 230 °C (446 °F) and a wet boiling point of at least 155 °C (311 °F). The word wet is not vague: it means the fluid has taken up 3.7 per cent water by volume, the point at which it counts as saturated. That is a drop of 75 °C, or 32.6 per cent of the dry figure, from water alone.
| Condition | Water content | Boiling point | Driven by |
|---|---|---|---|
| Fresh DOT 4, minimum spec | 0 % | 230 °C | New fluid |
| Saturated DOT 4, minimum spec | 3.7 % | 155 °C | Roughly two years of air |
| Change interval, DOT 4 | About two years, on the calendar | ||
| Change interval, DOT 3 | About one year, on the calendar |
A car that has covered 800 miles since its last fluid change and a car that has covered 20,000 are in the same condition on this one item, because the mechanism has nothing to do with distance. The stored car arguably has it worse, since a garage that keeps a car dry rarely keeps the air around it dry.
Tyres are replaced on a date, not on a depth
Tread depth is the test everyone knows and it is the wrong one for a car that does not move. Vehicle and tyre manufacturers, as summarised in NHTSA guidance, advise close inspection from around six years after manufacture and replacement by about ten years regardless of remaining tread. The date is readable on the sidewall: the last four digits of the DOT code are the week and the year, so a tyre marked 2325 left the factory in week 23 of 2025.
There is a genuine disagreement here worth knowing about. The European Tyre and Rim Technical Organisation position is that age alone is a poor test, that storage conditions dominate what actually happens to the rubber, and that inspection in service beats a fixed number. Both views are held by serious people. What neither view offers is a way for mileage to matter, which is the point: a set of tyres with 2 millimetres of wear and eleven years on the clock is a set of tyres that is being replaced.
On a car wearing a set worth 4,000, replacing on age at ten years costs 400 a year whether the car covered 100,000 miles or 8,000. Spread across the distance actually covered, that is 40 per 1,000 miles in the first case and 500 in the second, a factor of 12.5 on identical tyres fitted to identical cars.
The service book counts years
Manufacturer schedules for this class of car are written as a mileage figure or an elapsed period, whichever comes first, and the period is normally twelve months. A car that covers 1,200 miles in a year reaches its annual service on the calendar without ever approaching the distance trigger.
That single wording is what makes low use expensive per mile. The scheduled cost per year is close to unchanged. The scheduled cost per mile rises in inverse proportion to how little the car is used. A 2,400 annual service is 0.20 per mile at 12,000 miles a year and 2.00 per mile at 1,200.
The costs that never noticed the car stopped
- Insurance. A policy in force covers fire and theft in a garage. Laid up cover reduces it, but reduce is not remove.
- Storage. Charged by the month, entirely independent of use.
- Battery. A modern car draws current when parked, so a stored car needs a maintenance charger or it needs a battery.
- Tyres under load. A tyre left in one position takes a set in the contact patch, felt as vibration on a cold start.
- Depreciation. Continues on the calendar, and mileage moderates it rather than driving it.
Only fuel and genuinely distance related wear stop when the car stops. That is a short list against the one above.
What this means when buying
A delivery mileage car five years old is not a car with five years of life saved up. It is a car that is due, or overdue, on every calendar item in the book, and the person buying it inherits all of them at once. The premium such cars command is a premium for condition and for originality, and it is worth what the buyer thinks it is worth. It is not a discount on running cost.
The honest question to ask of any low mileage car is not how far it has gone. It is when the fluids were last changed, what date is stamped on the tyres, and whether the annual services were carried out in the years the car was not being driven.
Questions readers ask
Does a low mileage car really cost the same to service?
Per year, close to it. Manufacturer schedules are written as a mileage figure or an elapsed period, whichever comes first, and the period is normally twelve months. A car doing 1,200 miles a year reaches the annual service on the calendar and never gets near the distance trigger.
Why does brake fluid need changing if the car is not driven?
Because it absorbs water from the air rather than wearing out. DOT 4 must boil at no less than 230 °C when dry and no less than 155 °C once it holds 3.7 per cent water by volume, which takes roughly two years. That is a 75 °C fall, and driving has nothing to do with it.
How do I read the age of a tyre?
The last four digits of the DOT code on the sidewall are the week and the year of manufacture. A tyre marked 2325 was made in week 23 of 2025. Guidance summarised by NHTSA suggests close inspection from about six years and replacement by about ten.
Is the ten year tyre rule universally agreed?
No, and the disagreement is worth knowing. The European Tyre and Rim Technical Organisation argues that age alone is a poor test and that storage conditions matter more, favouring regular inspection over a fixed number. Neither position gives mileage a role.
Is a delivery mileage older car a bargain on running costs?
No. It is a car with every calendar item either due or overdue, inherited in one go by whoever buys it. Any premium it carries is for condition and originality, not for cheaper ownership.
What actually does get cheaper with low use?
Fuel and distance related wear: brake pad and disc wear, tyre tread wear, clutch wear. Everything driven by time carries on regardless, which is most of the annual bill on this class of car.
Sources
- NHTSA, tyre safety, on inspection from around six years, replacement by about ten, and reading the date of manufacture.
- DOT marking, week and year of manufacture, on how the four digit date code is read.
- Brake fluid boiling points, on dry and wet specification minimums and the 3.7 per cent water definition of saturated.
- Regulation (EU) 2020/740, for the wet grip classes referred to when comparing tyres on condition rather than age.