Checking your coolant level is the simplest yet most vital maintenance routine to keep your engine running healthy. Here are the proper inspection steps and key precautions to keep in mind:
Why? The cooling system operates under high temperature and pressure. Coolant expands when heated, meaning the fluid level inside the expansion tank will sit visibly higher than when cold. The MAX and MIN markings on the tank serve as an accurate benchmark only when the engine is completely cold.
Safety Warning: Never open the expansion tank cap while the engine is hot! Pressurised steam and boiling liquid will spray out instantly, causing severe burn injuries.
Park the vehicle: Park on level ground, switch off the engine, and wait at least 30 minutes to allow the engine to cool down fully.
Locate the expansion tank: Pop the bonnet and look for the translucent plastic reservoir (usually labelled "Coolant", containing pink or green fluid).
Check the fluid level:
Look directly through the translucent reservoir wall to check the fluid level.
The coolant level should sit between the MIN and MAX markings.
Top up if necessary:
If the fluid level drops below the MIN mark, a top-up is needed.
Top-up guidelines: Always aim to use coolant that matches the exact colour and specification of the current fluid in your car. If unsure or if only a minor top-up is required, distilled or battery water can be used as an emergency fix (make sure to visit a workshop soon after to restore the correct coolant-to-water ratio).
Never mix coolants: Do not mix different coolant colours or chemical formulations (such as organic OAT vs inorganic IAT types). Incompatible coolants can react, forming a gel-like sludge that clogs the engine's cooling passages.
Persistent coolant loss: If the level drops from MAX to MIN or lower over a short period, there is a leak in the system. Inspect the radiator, water pump, hose joints, and the expansion tank itself for any signs of seepage.
Murky or discoloured coolant: If the coolant turns black, contains floating debris, or looks milky and oily (a sign of engine oil contamination), this usually points to a severe internal fault such as a blown head gasket. Send the car for inspection immediately.
Crystalline residue around the cap: If you spot dried white or coloured crusty residue around the cap edges, the cap's pressure seal has deteriorated. Replace the cap promptly to prevent pressure loss that can lead to engine overheating.
"The more fluid, the better": Never fill past the MAX line. Coolant requires expansion space; overfilling will cause hot fluid to bleed out through the pressure relief valve, potentially corroding surrounding components in the engine bay.
Relying on tap water long-term: Many car owners simply top up with tap water whenever the level drops. Doing this continuously dilutes the coolant concentrate, raising the freezing point and completely stripping away anti-rust properties, which leads to rust, scale build-up, and choked cooling passages.
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