You check the coolant reservoir and the level is low.
You top it up.
A few days or weeks later, it's low again.
Maybe there's a puddle underneath the vehicle.
Maybe you can smell coolant after driving.
Or perhaps there's absolutely no obvious sign of where it's going.
One thing is important:
COOLANT SHOULDN'T NEED CONSTANT TOPPING UP.
Your vehicle's cooling system is designed to retain its coolant. If the level keeps dropping, we need to establish where that coolant is going and why.
At The Cape Brake Co, topping up the reservoir might get the level back where it belongs.
It doesn't repair whatever caused the coolant to disappear.
HOW MUCH COOLANT LOSS IS NORMAL?
A healthy, sealed cooling system shouldn't routinely require significant amounts of coolant to be added.
The level in an expansion tank can change slightly depending on whether the engine is hot or cold, which is why the reservoir normally has level markings.
But if you're regularly adding coolant because the level keeps dropping below the appropriate mark, that deserves investigation.
Especially if the pattern is:
TOP UP → DRIVE → LEVEL DROPS → TOP UP AGAIN
The coolant is going somewhere.
WHERE CAN COOLANT LEAK FROM?
Modern cooling systems contain numerous components, hoses, seals and connections.
Depending on the vehicle, possible external leak points can include:
- Radiator
- Upper and lower radiator hoses
- Smaller coolant hoses
- Hose connections and clamps
- Expansion tank
- Radiator or expansion-tank cap
- Thermostat housing
- Water pump
- Coolant pipes
- Heater hoses
- Heater core
- Seals and gaskets
- Other cooling-system connections
Some leaks are immediately obvious.
Others can be surprisingly difficult to find.
WHY CAN'T I SEE A PUDDLE?
Because not every coolant leak reaches the floor.
A small leak may occur only when the cooling system is hot and pressurised.
Coolant may escape onto a hot engine component and evaporate before enough reaches the ground to form a puddle.
It may also collect on:
- Undertrays
- Engine covers
- Crossmembers
- Gearbox housings
- Other components beneath the leak
Airflow while driving can spread coolant away from its original source too.
So:
NO PUDDLE DOESN'T AUTOMATICALLY MEAN NO LEAK.
WHAT DOES A COOLANT LEAK LOOK LIKE?
That depends partly on the coolant being used.
You may see:
- Wetness around a connection
- Coloured residue
- Crystallised deposits
- Dried staining
- Damp hoses
- Coolant collecting on an undertray
- A visible drip
- A larger puddle beneath the vehicle
But don't rely entirely on colour.
Coolants are available in different colours, and colour alone isn't a reliable way to identify the correct coolant specification for a vehicle.
WHY CAN I SMELL COOLANT BUT NOT SEE A LEAK?
This is quite common with smaller leaks.
Coolant escaping onto a hot component can produce a noticeable sweet or chemical smell without leaving a large visible puddle.
If you repeatedly smell coolant after driving, particularly around the engine bay, tell us.
Your nose may have noticed the problem before your driveway does.
CAN A RADIATOR LEAK COOLANT?
Yes.
Radiators can develop leaks because of issues such as:
- Corrosion
- Physical damage
- Age
- Cracked tanks
- Damaged seams
- Impact from road debris
- Connection problems
A leak may be obvious, or it may only appear when the system reaches operating temperature and pressure.
The radiator should therefore be inspected as part of a coolant-loss investigation.
CAN A HOSE CAUSE A COOLANT LEAK?
Absolutely.
Cooling-system hoses spend their lives exposed to heat, pressure, vibration and ageing.
Over time, a hose can potentially:
- Crack
- Split
- Harden
- Soften
- Swell
- Leak around a connection
- Become damaged through contact with another component
Sometimes the hose itself is fine and the leak is coming from the connection or sealing surface.
That's why we want to identify the actual source rather than replacing whichever hose happens to look old.
CAN THE EXPANSION TANK LEAK?
Yes.
Plastic coolant reservoirs can deteriorate with age and repeated heat cycles.
Cracks can sometimes be extremely small and only open sufficiently to leak once the system becomes hot.
The tank's connections and cap can also need attention.
If there is dried coolant residue around the reservoir, that's useful evidence.
CAN A BAD COOLANT CAP CAUSE COOLANT LOSS?
Potentially.
The cap isn't simply a lid.
Depending on the cooling-system design, it forms part of the system's pressure control.
If it doesn't operate or seal correctly, cooling-system behaviour can be affected.
Coolant may escape or the system may not maintain pressure as intended.
A small component can therefore cause a surprisingly frustrating problem.
HOW CAN A WATER PUMP LEAK?
The water pump circulates coolant through the engine and cooling system.
Depending on its design, deterioration of the pump's seal can allow coolant to escape.
Some pumps have a drain or weep area that can provide evidence of seal failure.
But water pumps aren't always conveniently positioned where you can see them.
On some engines, the pump can be partly concealed behind covers or other components.
That can make the source of coolant loss less obvious.
CAN THE THERMOSTAT HOUSING LEAK?
Yes.
Thermostat housings and their seals are another possible source of coolant leakage.
Many modern engines use plastic cooling-system housings and fittings.
Years of heat cycling can take their toll.
Again, that doesn't mean:
“PLASTIC HOUSING = REPLACE IT.”
It means the area should be inspected if the evidence points there.
CAN COOLANT LEAK INSIDE THE CAR?
Yes.
The vehicle's heater typically uses hot engine coolant flowing through a heater core inside the HVAC system.
A heater-core leak can potentially produce symptoms such as:
- Coolant smell inside the cabin
- Damp carpeting
- Unusual moisture
- Windscreen misting
- Coolant loss without an obvious engine-bay leak
The exact symptoms vary by vehicle and severity.
But if the inside of the car smells strongly of coolant, tell us.
WHAT IF THERE IS ABSOLUTELY NO EXTERNAL LEAK?
Then we may need to investigate whether coolant is being lost internally.
Possible internal coolant loss can involve engine components such as:
- Cylinder-head gasket
- Cylinder head
- Engine block
- Certain oil coolers
- EGR coolers on some engines
- Other vehicle-specific components
This is where diagnosis becomes particularly important.
COOLANT LOSS DOES NOT AUTOMATICALLY MEAN A BLOWN HEAD GASKET.
There are many possible external causes that should also be considered.
CAN A HEAD GASKET CAUSE COOLANT LOSS?
Yes.
A head-gasket failure can potentially allow coolant to move somewhere it shouldn't.
Depending on the type and location of the failure, coolant might enter:
- A combustion chamber
- An oil passage
- Another part of the engine
Combustion gases may also enter the cooling system.
But a failed head gasket is only one possible explanation for coolant loss.
We don't want to jump from:
“MY COOLANT IS LOW”
straight to:
“YOU NEED AN ENGINE REBUILD.”
There needs to be evidence.
DOES WHITE SMOKE MEAN MY HEAD GASKET IS BLOWN?
Not automatically.
Visible white exhaust vapour can have different causes and needs to be interpreted in context.
Condensation from an exhaust during a cold start, for example, isn't the same thing as persistent coolant entering a combustion chamber.
If you have:
- Persistent white exhaust smoke or vapour
- Coolant loss
- Overheating
- Poor engine operation
- Cooling-system pressure problems
then the combination deserves investigation.
One symptom by itself doesn't always provide the diagnosis.
WHAT IF MY ENGINE OIL LOOKS MILKY?
Coolant contamination can sometimes affect the appearance of engine oil.
However, not every creamy deposit seen under an oil cap proves coolant is entering the engine oil.
Short journeys and condensation can sometimes produce deposits in certain areas too.
If coolant loss is occurring alongside suspicious oil contamination, then further investigation is sensible.
Again:
LOOK AT THE WHOLE PICTURE.
HOW DO YOU FIND A COOLANT LEAK?
The appropriate process depends on the vehicle and symptoms.
Diagnosis may involve:
- Visual inspection
- Checking coolant level and condition
- Inspecting hoses and connections
- Looking for dried coolant residue
- Inspecting the radiator
- Checking the expansion tank
- Inspecting accessible areas around the water pump
- Checking thermostat housings and coolant fittings
- Cooling-system pressure testing
- Checking heater-system components
- Investigating possible internal coolant loss where necessary
A cooling-system pressure test can be particularly useful because it allows the system to be checked for leakage under controlled pressure.
WHAT IS A COOLING-SYSTEM PRESSURE TEST?
The cooling system normally operates under pressure once the engine reaches operating temperature.
A suitable pressure-testing tool allows a technician to apply controlled pressure to the cooling system while the engine isn't necessarily running at full operating temperature.
We can then inspect the system for signs of leakage.
A small leak that isn't obvious when the engine is cold may become easier to identify once the system is pressurised.
It doesn't magically locate every possible cooling-system fault.
But it can be a very useful diagnostic tool.
WHY DOES MY COOLANT ONLY LEAK WHEN THE ENGINE IS HOT?
Heat changes things.
As the engine reaches operating temperature:
- Coolant expands
- System pressure increases
- Components expand
- Seals and joints experience different conditions
A tiny crack or weak seal may therefore remain dry when the vehicle is cold and begin leaking once everything heats up.
This is one reason coolant leaks can sometimes seem to disappear when the vehicle reaches the workshop.
CAN COOLANT LEAK ONLY AFTER I SWITCH THE ENGINE OFF?
Yes.
Cooling-system temperature and pressure don't necessarily disappear the instant the engine stops.
In some circumstances, heat within the engine can continue transferring into the coolant after shutdown.
A leak may therefore become more noticeable shortly after the vehicle has been parked.
If you notice a puddle appearing after a drive rather than during it, tell us.
That timing is useful.
WHY SHOULDN'T I JUST KEEP TOPPING IT UP?
Because you're managing the symptom rather than repairing the fault.
Repeated topping-up creates several risks.
The leak may become worse.
You may eventually lose coolant faster than expected.
The engine may overheat.
And if the coolant is being lost internally, continuing to drive could allow a more serious problem to develop.
A small leak is usually much nicer to deal with before the temperature gauge reaches the red.
CAN I USE STOP-LEAK?
We generally prefer to repair the actual source of the leak.
Cooling-system sealing products are designed to circulate through the same system containing:
- Radiator passages
- Heater-core passages
- Thermostat
- Water pump
- Small coolant galleries
Introducing a substance intended to seal a leak can potentially have consequences elsewhere in the system.
A bottle may look considerably cheaper than repairing a leaking component.
But we'd rather know what is leaking and fix it properly.
WHAT SHOULD I TOP UP WITH?
Ideally, the correct coolant specification and mixture for the vehicle.
Different manufacturers can specify different coolant formulations.
Don't choose coolant purely because:
“THE ONE IN MY CAR IS PINK.”
or:
“THIS ONE IS ALSO GREEN.”
Colour isn't a technical specification.
If you don't know what coolant belongs in the vehicle, check the manufacturer's information or ask us.
NEVER OPEN A HOT COOLING SYSTEM
This deserves repeating.
A hot cooling system may be under significant pressure.
Removing the radiator or expansion-tank cap while the system is hot can allow extremely hot coolant and steam to escape suddenly.
That can cause serious burns.
If the engine has overheated:
LET IT COOL.
Don't lean over the reservoir and immediately remove the cap.
WHAT SHOULD I TELL CBC?
If your vehicle is losing coolant, tell us:
- Make
- Model
- Year
- VIN
- Approximate mileage
- How frequently you're topping it up
- Roughly how much coolant you're adding
- Whether you've seen a puddle
- Where the puddle appears
- Whether you can smell coolant
- Whether the engine has overheated
- Whether the heater behaves normally
- Whether you see white exhaust smoke or vapour
- Whether any cooling-system work has recently been carried out
- What coolant you've been adding, if known
Photos can be extremely useful.
If you see a leak or dried residue, take a picture before cleaning it away.
THE CBC APPROACH TO COOLANT LOSS
At The Cape Brake Co, we don't want the repair process to be:
LOW COOLANT → TOP IT UP → SEE YOU AGAIN NEXT WEEK.
We want to know:
WHERE IS IT LEAKING?
WHEN DOES IT LEAK?
IS THE SYSTEM HOLDING PRESSURE?
IS THE LOSS EXTERNAL OR INTERNAL?
WHAT COMPONENT ACTUALLY NEEDS ATTENTION?
Then we can repair the cause rather than repeatedly treating the symptom.
KEEP HAVING TO TOP UP YOUR COOLANT?
If the coolant level keeps dropping, you're finding puddles beneath the vehicle or you can smell coolant after driving, contact The Cape Brake Co.
And if the vehicle is also overheating, don't continue driving it simply because you've topped the reservoir up again.
The coolant went somewhere. Let's find out where.
Ask the Workshop Assistant or WhatsApp The Cape Brake Co.
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