Check the core plugs in the side of the cylinder block. Check all hose connections for tightness, but ensure that the clips are not cutting into the
rubber. Look along the hose for cracks, especially at points where the hose is flexed by engine movement.
Inspect the radiator seams for splits, also the catch tank and its pipe. Watch for leaks at the water-pump bearings and from the pump gasket.
Check the thermostat housing for cracks, and the housing gasket for leaks.
A rising temperature gauge, a pool of coolant beneath the car and a drop in the radiator level are signs of a leak. So are rust-coloured stains in the engine bay.
But if you cannot actually see the leak, a systematic check is called for.
Always work when the engine is hot, and pressure in the cooling system has built up – forcing out coolant at any weak spot.
The likely sources of leaks are where a hose is flexed by engine movement over the end of the stub to which it is fitted, or where an overtightened clip has bitten into the rubber.
Seams at the top and bottom of the radiator are also danger spots.
Small leaks can sometimes be cured by sealing preparations available from shops and garages. But leakage from a radiator seam is best left to a garage.
Some cars have plastic coolant tanks, and leaks in them are also beyond do-it-yourself repair.
Always treat them gently – using a screwdriver to lever off an old hose can easily break off the stub.
Inspect hoses carefully at bends and joints, as well as where they clip on to stubs (See Checking hoses and the radiator cap).
Core plugs, which fill holes left in the cylinder block when it is being cast, are other likely sources of leaks. They may be blown loose by pressure from the system, corroded, or even loosened by vibration.