Coolant change and frost protection check

Symptoms worth having checked

Book a time if you notice any of these:

• the coolant is brown, rusty or cloudy, or there is oil on its surface in the expansion tank
• the level drops and the tank has to be topped up again and again
• there are coloured drops under the car or a sweet smell from under the bonnet
• the heater blows cool air although the engine is warm, or there is a sweet smell in the cabin
• the engine warms up slowly or the temperature gauge stays lower than usual
• the temperature gauge climbs higher than usual or the coolant warning light comes on

Many of these are not fixed by changing the coolant alone. If coolant disappears, there is a leak somewhere. An engine that warms up slowly often has a thermostat stuck open, and oil in the coolant points to the cylinder head gasket or the oil cooler. So we first find out what causes the symptom.

When the change is due

The interval is set by the car's manufacturer and written in the service book or the service schedule. It varies a great deal with the make and the coolant. On older cars and with conventional coolants it is often two to five years.

With long-life coolants the interval is much longer. For many manufacturers the first change comes only at 5–15 years or 150 000–250 000 km, whichever comes first. Some manufacturers set no change at all, and the coolant's condition and frost protection are checked at services instead.

The change is also worth doing when the service history is unknown, for example on a used car you have just bought, or when plain water has been added to the coolant. It can be combined with a scheduled service.

Frost protection before the winter

The mixture's frost protection depends on the share of antifreeze. When antifreeze and water are mixed half and half, the mixture typically withstands about −36 °C, which is usually enough for a winter in the Helsinki region. Volkswagen's instructions, for example, put the antifreeze share at no less than 40 % and no more than 60 %. A stronger mixture does not improve the frost protection but weakens it, and the coolant also cools less well.

If water was added to the tank in the summer, the frost protection may have dropped a lot. Freezing coolant expands and can crack the radiator, the heater core or, at worst, the engine block. Measuring the frost protection takes only a moment. The coolant does not need changing if it is clean, the frost protection is enough and the manufacturer's interval has not yet been reached.

Fitting a block or hose heater usually means draining coolant anyway. If the car has no engine heater, block heater installation and the coolant change are therefore worth doing on the same visit.

How the change is done

1. We check which coolant the manufacturer requires and how much the system takes. The type cannot be told from the colour, because coolants of the same colour can be of different types and the same type is sold in different colours.
2. We measure the old coolant's frost protection and look at its colour and cleanliness. If there is rust, sediment or oil in it, we tell you before we go on.
3. Once the engine has cooled, we drain the old coolant from the radiator drain plug or the lower hose. On some cars coolant is also drained from the engine block.
4. We fill the system with new coolant. We dilute the antifreeze to the concentration in the manufacturer's instructions, or use a ready-diluted coolant.
5. We bleed the system to the manufacturer's instructions. Air left in the system is a common reason an engine overheats or the heater blows cold after a change. On some cars the bleeding is done with a diagnostic tool that runs the car's electric water pump.
6. We run the engine until it is warm and check that the fan cuts in, the heater blows warm and no connection leaks. Finally we set the coolant level and measure the frost protection.

How long it takes

The work itself usually takes from half an hour to a little over an hour. A flush, more than one cooling circuit and a system that is hard to bleed make it longer. We tell you the expected time when we agree the booking.

What affects the price

The price of the change varies from car to car. What affects it most:

• The amount of coolant. A small car's system takes about five litres, a large engine's over ten.
• The type of coolant. Prices per litre differ a lot, and some cars take only the manufacturer's own coolant.
• The bleeding. Some systems are slow to bleed, and on some the bleeding is done with a diagnostic tool.
• Draining. If the radiator has no drain plug, or an undertray has to come off, draining the coolant takes longer.

A flush and changing the coolant in other circuits are priced separately. We check the car and tell you the price before the work starts. If something turns up during the work that changes the price, we call you before we go on.

Coolant and the inspection

Coolant is not an inspection item of its own, but the inspector looks under the car for leaking oil and other fluids. Under Traficom's inspection criteria, a fluid leak that forms drops gets a repair notice. If drops form continuously, the car fails. A leak that causes a fire risk leads to a driving ban.

In Traficom's inspection statistics for 2025, 200 rejecting faults and 3 045 repair notices were recorded for fluid leaks. Oil leaks and fuel leaks are counted separately.

On a diesel car taken into use from the start of 1980 to the end of August 2016, the exhaust is measured with a smoke opacity test. Before the test the inspector checks that the engine has the right amount of oil and coolant.

A repair notice does not stop the car passing, but a dripping leak is worth fixing before the winter. Every time water is added to a leaking system, the frost protection weakens. Read more about inspection repairs.

Checking and topping up the coolant yourself

• The level. Look at the level in the expansion tank when the engine is cold. It should be between the MIN and MAX marks.
• The cap. Do not open the expansion tank cap while the engine is warm. The system is then under pressure, and hot coolant can spray out.
• Topping up. Add only the coolant the manufacturer requires, at the right concentration. The owner's manual tells you the right type. Different types should not be mixed, because some coolants form sediment when mixed. If you add water in an emergency, mention it at the next service so the frost protection gets measured.
• Leaks. Look at your parking spot for drops under the car. Coolant is dyed, usually green, blue, red, pink, orange or violet, and it smells sweet. Clear, odourless water under the car is usually condensation from the air conditioning.

Coolant is poisonous, and its sweet taste attracts pets. Wipe up any spill and take old coolant to a hazardous waste collection point.

When not to drive the car

Stop somewhere safe and switch off the engine if you notice any of these:

• the temperature gauge climbs into the red, or the red coolant warning light comes on
• steam rises from under the bonnet
• the expansion tank is empty, or coolant is running out under the car
• white, sweet-smelling smoke still comes from the exhaust after the engine has warmed up

An overheated engine can be damaged within a few minutes: the cylinder head gasket can fail or the head can warp. Let the engine cool before you open the cap, and do not pour cold coolant into a hot engine.

If the coolant has leaked away or white smoke comes from the exhaust, the car has to come to the workshop on a tow truck. Call us and we will agree a time.