There is no sign of antifreeze dripping on the ground beneath your vehicle, but you frequently add coolant and continuously find your Mitsubishi Fuso, Isuzu, Hino, or UD freight truck low on antifreeze. Where is it going?
Coolant can leak from the water jacket into several parts of the engine. The most common leaks are –
Oil galley / return (ends up in the oil pan) – A visual inspection of the oil, oil dipstick, oil filler cap and PCV valve may show a white, milky film of homogenized oil and coolant. An increase in oil level or the bittersweet smell of ethylene glycol on the dipstick are solid evidence of a significant internal leak.
Combustion chamber – The smell of coolant or a whitish cloud of smoke from the exhaust at start-up can be an indicator of coolant in the combustion chambers. If this is the case, it can be confirmed by a chemical test for exhaust hydrocarbons in the coolant.
Heater Core – The heater core is located inside the heating ventilation and air conditioning (HVAC) unit under the dash. It is out of sight so you cannot see a leak directly. Look for stains or wet spots on the bottom of the plastic HVAC case, or on the passenger side floor.
Water pump – If you have a bad shaft seal, coolant can dribble out of the vent hole just under the water pump pulley shaft. If the water pump is a two-piece unit with a backing plate, the gasket between the housing and back cover may be leaking. The gasket or o-ring that seals the pump to the engine front cover on cover-mounted water pumps can also leak coolant. Look for stains, discoloration or liquid coolant on the outside of the water pump or engine.
Intake Manifold gasket – The gasket that seals the intake manifold to the cylinder heads may leak and allow coolant to enter the intake port, crankcase or dribble down the outside of the engine.
Radiator – Radiators can develop leaks around upper or loser hose connections as a result of vibration. The seams where the core is mated to the end tanks is another place where leaks frequently develop, especially on aluminum radiators with plastic end tanks. On copper/brass radiators, leaks typically occur where the cooling tubes in the core are connected or soldered to the core headers. Internal corrosion caused by old coolant that has never been changed can also eat through the metal in the radiator, causing it to leak.
Hoses – Cracks, pinholes or splits in a radiator hose or heater hose will leak coolant. A hose leak will usually send a stream of hot coolant spraying out of the hose. A corroded hose connection or a loose or damaged hose clamp may also allow coolant to leak from the end of a hose. Sometimes a leak may only occur once the hose gets hot and the pinhole or crack opens up.
Freeze plugs – These are the casting plugs or expansion plugs in the sides of the engine block and/or cylinder head. The flat steel plugs corroded from the inside out, and may develop leaks that are hard to see because of the plug’s location behind the exhaust manifold, engine mount or other engine accessories. On V6 and V8 blocks, the plugs are most easily inspected from underneath the vehicle.
Relatively simple, inexpensive tests can identify specific internal coolant leaks.