Why you should always check the coolant in a used car

A used car can look immaculate inside while hiding a cooling problem. In Australia, a vehicle may arrive through a dealer, a private sale or an interstate listing. The engine bay should tell you more than the paint, but coolant is often overlooked until the temperature needle climbs. That is not a risk worth taking on a hot Brisbane or Sydney afternoon.

Coolant carries heat away from the engine and protects metal from corrosion. Freeze protection matters less in many parts of Australia, but summer heat, long drives and heavy towing still place a cooling system under considerable pressure. A used car may have the wrong fluid, a weak cap, perished hoses or evidence of previous overheating.

What a clean engine can still hide

Start with the expansion tank, radiator cap and surrounding engine bay. The coolant level should sit within the manufacturer’s markings when the engine is cold. Look for coloured staining below the tank, around the cap or beneath the radiator, as these can indicate a slow leak that a seller may have wiped away.

A clean engine bay is helpful but not conclusive. Ask whether the cooling system has been serviced or repaired, and why. If the seller mentions recent work, review signs of proper repair for clues such as correct parts, documented invoices and evidence that the repair addressed the actual fault.

Read the paperwork and service history

Request the servicing logbook or electronic records before inspecting the car. Look for radiator and coolant replacements, thermostat or water pump work, cooling fans, air-conditioning repairs and any mention of overheating. A service history that skips several years is a warning sign, particularly if the mileage suggests the car should have travelled much further.

In NSW, ask whether the pink slip and rego transfer are complete; neither proves the engine was maintained properly. Interstate buyers should also check whether earlier servicing was recorded under another registration. The same preventive discipline appears in motorcycle chain maintenance, where regular adjustment and inspection prevent a small mechanical issue from becoming a failure.

Inspect the cooling system safely

Do not remove the radiator cap from a hot engine, even if the engine has been switched off. Pressurised coolant can erupt and cause severe burns. Instead, inspect the cap for cracks, a damaged seal or a mismatch with the vehicle, and examine hoses for softness, swelling, bulges and weeping.

Check the coolant’s appearance and identify its specification. Colour is not a reliable guide because different products can look similar. Confirm that the correct coolant was used and that different formulations have not been mixed. An independent pressure test can reveal leaks that remain invisible while the engine is cold.

Test the car under real load

Ask the seller to drive the car so you can watch the temperature gauge. A short trip around the block may not reveal a problem with the radiator, fan clutch, thermostat or cooling fan. Traffic, air-conditioning and a steady highway drive provide a better test, including a longer run such as Melbourne to Adelaide.

If the temperature rises unusually, the gauge behaves erratically or a warning light appears, stop safely and arrange a tow rather than continuing. Also examine the quality of any recent repairs. Correct components matter throughout the vehicle, and brake rotor sizing illustrates why matching dimensions and specifications is preferable to choosing replacement parts by appearance alone.

A practical coolant checklist for an Aussie inspection

Use this sequence before signing the contract or transferring the funds:

• Check the expansion tank level against the manufacturer’s cold-engine markings.
• Inspect the radiator cap, coolant hoses, radiator and visible pipework for damage.
• Look for coloured stains, oily residue, rust or signs of a previous leak.
• Confirm the coolant type, concentration and service dates from the records.
• Ask about overheating incidents, towing, cooling-system repairs and replaced parts.
• Arrange a pressure test and an independent pre-purchase inspection.
• Take a longer test drive while monitoring the temperature gauge closely.

A low reservoir reading may point to a leak, an incorrect mixture or a component that is not holding pressure. Do not simply add water and assume the problem is solved; some engines are sensitive to diluted coolant or contamination.

Before handing over the money, make coolant part of the same inspection routine you would use for tyres, brakes and service records. For more used-car guidance and practical automotive walkarounds, visit Pissin Autopod and use this checklist during your next inspection.