The 30-second version
- Overheating can warp a cylinder head or blow a head gasket in minutes — it's one of the fastest ways to write off an engine.
- Milky, mayonnaise-coloured coolant usually means oil is mixing with it — a serious, expensive red flag.
- A temperature gauge that climbs steadily and doesn't settle back down is not normal, even in SA traffic and heat.
- Staining or crustiness around hose joints and the radiator suggests a slow leak, even if the coolant level looks fine today.
- A low coolant level topped up with plain water can temporarily hide a leak — a full check matters more than a quick glance.
The cooling system doesn't get the attention the engine itself does, but it's one of the fastest ways a used car can turn into a very expensive mistake. An engine that overheats even briefly can warp a cylinder head or blow a head gasket — damage that can cost more to fix than the car is worth. None of the checks below need special tools, and they take a few minutes at most.
Checking the coolant itself
Open the coolant reservoir (never the radiator cap on a hot engine) and look at both the level and the condition of the fluid. Colour varies by brand and formulation — green, pink, blue and orange/red are all normal — but the fluid should look clean and consistent.
Radiator, hoses and visible leaks
What to check
- Hose condition — squeeze the upper and lower radiator hoses cold. They should feel firm, not spongy, brittle, or collapsed.
- Staining around joints — white or rusty-brown crusting around hose clamps or the radiator itself suggests a slow, ongoing leak.
- Radiator fins — heavily corroded, bent or clogged fins reduce cooling efficiency, especially in SA's hotter regions.
- Under the car — check for coolant staining (usually a sweet-smelling, often greenish patch) on the ground where the car has been parked.
- Water instead of coolant — a reservoir topped up with clear water rather than proper coolant is often a sign someone was hiding a leak rather than fixing it, and offers far less freeze/corrosion protection.
Watching the temperature gauge on the test drive
Start the car cold and watch the temperature gauge climb to its normal operating position and hold steady there. During the test drive, pay attention to how it behaves in slow-moving traffic — a common stress test for a marginal cooling system in SA's heat.
Also switch the cabin heater to full hot partway through the drive. A working heater relies on hot coolant circulating through it — if the air stays cool, that can point to low coolant, an airlock, or a failing water pump.
Common mistakes
- Only checking coolant level and skipping colour/condition — a full-but-milky reservoir is worse than a slightly low but clean one.
- Opening a hot radiator cap — this is genuinely dangerous, never do it on a warm engine.
- Assuming a full coolant level on the day means there's no leak — recent topping-up can mask a slow drip.
- Ignoring a brief warning light "because it went away" — intermittent overheating warnings still indicate a real developing problem.
Frequently asked questions
Buying soon? Check the whole engine bay, not just cooling.
Our Engine Bay guide covers fluids, belts, turbo and cooling checks in full — with red flags, SA repair costs and walk-away triggers.
Get the Engine Bay Inspection Guide — R75 →This guide is general information for South African motorists, not a substitute for a professional inspection. Repair costs vary by make and model. If you suspect a cooling system problem, have it assessed by a qualified mechanic before committing to buy.
Our Engine Bay guide covers cooling, fluids, belts and turbo checks in full — with red flags, SA repair costs and walk-away triggers.
Get the Engine Bay Inspection Guide — R75 →