The big winter service

Winter is frightening for a driver, especially a novice, for two reasons — black ice and hard frost. While preparing for black ice means choosing the right tyres, checking the suspension and sharpening your driving skills, preparing for the frost means getting practically every major system on your car ready.

Believe me, anything you forgot (or didn't know) to do for your car will most likely show up the moment the first frosts hit. That's why you need to prepare for winter in advance. Which engine oils are right for winter, and what else needs doing before the first frosts? What should the big pre-winter service actually cover?

Besides that, this article also touches a little on how, in my view, to correctly choose gear oils and other operating fluids.

Where to start and in what order

Start not at the shop but with the service book. The most convenient time for the big service is October and early November: it is still above zero in the daytime, and the queues at garages that appear after the first snow are not here yet. The priorities are simple: first what engine starting and safety depend on (oil, fuel, battery, brakes, tyres), then what can freeze (coolant, washer fluid), and only then everything else.

A list you can get through in one evening:

• note the date and mileage of the last engine oil and filter change;
• check the freezing point of the coolant;
• find out when the brake fluid was last changed;
• look at the levels in the power steering, brake and washer reservoirs;
• assess the battery and the wiper blades;
• book your tyre fitting while there are no queues.

Engine oil, filters and fuel

If less than half of the interval is left before the scheduled change, I change the oil in autumn rather than in spring. Over a season used oil picks up soot, fuel and oxidation products, thickens, and part of its additives is already spent. Fresh oil reaches the bearing shells and the camshaft faster on a cold start, and it is the first seconds after starting in frost that cause the most wear.

The viscosity is the one given in the owner’s manual, together with the manufacturer’s approval (ACEA, API or the carmaker’s own specification). The number before the W describes how the oil behaves in the cold: under SAE J300, a 0W oil must allow the engine to be cranked down to roughly −35 °C, 5W down to −30 °C, 10W down to −25 °C. There is no separate “winter” oil today. Moving one step down, for example from 10W-40 to 5W-40, makes sense only when the manual permits both grades for your climate; the second number is left unchanged. More on this in the article on winter engine oil.

The oil filter is changed together with the oil every time; the air filter is inspected and replaced if necessary. For a diesel the fuel filter matters most: water in it freezes, and in frost the paraffin in the fuel clogs the filter element. If the filter has a drain tap for sediment, drain the water before the first frosts; if the filter is already at the end of its interval, replace it now. When the season begins, fill up with winter diesel at reliable filling stations, don’t drive with an almost empty tank, and don’t pour anti-gel “just in case” into fuel that has already gelled — how to use it properly is explained in the piece on anti-gel additives.

Gearbox and axle

The manual gearbox, rear axle and transfer case are filled with oil of the API GL class and the viscosity that the manufacturer specifies. GL-5 is not always “better” than GL-4: many gearboxes with synchronisers need exactly GL-4, because the active additives of GL-5 can harm parts made of non-ferrous metals. It used to be common to put thinner oil into the gearbox and axle for winter and thicker oil in spring. Modern all-season 75W-80 and 75W-90 oils have done away with this practice, so there is no need to change gear oil “for the season”. Many manual gearboxes are maintenance-free anyway — all you check is the level and that nothing leaks.

An automatic gearbox, a CVT or a wet-clutch automated manual takes only a fluid that meets the manufacturer’s specification: a particular ATF standard or a special CVT fluid. A universal fluid “for all gearboxes” is no substitute here. Take the interval from the service book; if it says “lifetime” and the car does a lot of city driving, consult a specialist workshop. A list of what else to check in the transmission is in the article on gear oil and other fluids.

Coolant, brake fluid and other fluids

The freezing point of the coolant is measured with a hydrometer or, more accurately, a refractometer. Ready-mixed antifreezes are usually rated for roughly −35…−40 °C. If you topped up with water in summer, the check is a must: diluted coolant can freeze and damage the radiator or the block. Different types are not mixed — old-type Tosol with a carboxylate antifreeze, fluids of different technologies — and colour is no guide here. The interval runs from two or three years for old-type fluids to five and more for modern long-life ones. How to check the condition of the fluid is described in detail in the article what antifreeze is.

DOT 4 brake fluid is hygroscopic: it absorbs moisture from the air, and its boiling point drops every year. For fresh DOT 4 the standard requires at least 230 °C, for moisture-laden fluid only 155 °C. In winter the moisture in the system adds corrosion as well. The fluid is changed roughly every two years unless the service book says otherwise; silicone DOT 5 is not mixed with DOT 3, DOT 4 and DOT 5.1.

In the power steering reservoir you check the level and top up only with the fluid that is already there: ATF or a special power steering fluid. Many modern cars have electric power steering, with no fluid at all. The washer reservoir is filled with winter fluid with a margin on temperature, and the remains of the summer fluid are used up beforehand; concentrate is diluted no more than the label says.

Battery, spark plugs, wipers and tyres

In the cold a battery delivers less current, and the starter has to turn an engine full of thick oil. The resting voltage of a fully charged battery is about 12.6–12.7 V; if you measure 12.4 V or lower, the battery should be recharged, and if it is already five or six years old, have it load-tested at a workshop. While you are at it, clean and tighten the terminals. Spark plugs are changed on schedule; on a diesel you check the glow plugs — a hard cold start and white smoke often point to them.

It is better to fit new wiper blades, and never tear off ones that have frozen to the glass. Winter tyres are usually fitted once the average daily temperature stays steadily below +7 °C. Whether winter tyres are compulsory differs from country to country, so check the rules where you drive. The legal minimum tread depth for cars in the EU is 1.6 mm, but for winter that is not enough — you want at least 4 mm. For the rest of the winter habits behind the wheel, see the 10 rules of winter driving.

What to do yourself and what to leave to a workshop

Quite realistically you can do the following yourself: check the levels and top up the fluids, replace the washer fluid and the wipers, measure the battery voltage, check the antifreeze with a hydrometer and drain the sediment from the diesel filter if it is easy to reach. The oil and filter change is also within reach if you have an inspection pit and somewhere to take the used oil; pouring it on the ground or down the drain is not allowed. Leave to a workshop the brake fluid change (on cars with ABS it is sometimes bled with a scan tool), servicing of automatic gearboxes and CVTs, where the level is checked at a particular fluid temperature, the diesel fuel filter replacement, the battery load test and tyre fitting. And ask them to write the dates and mileage of all the replacements in the service book — next autumn that will save you time.

Read the whole “Winter driving” section