WHERE COOLANT LEAKS OCCUR
Coolant leaks can occur anywhere in the
cooling system. Nine out of ten times, coolant leaks are easy to find
because the coolant can be seen dripping, spraying, seeping or bubbling
from the leaky component. Open the hood and visually inspect the engine
and cooling system for any sign of liquid leaking from the engine,
radiator or hoses. The color of the coolant may be green, orange or
yellow depending on the type of antifreeze in the system. The most
common places where coolant may be leaking are:
Water pump -- A bad
shaft seal will allow coolant to 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.
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. The core itself
is also vulnerable to stone damage. Internal corrosion caused by old
coolant that has never been changed can also eat through the metal in
the radiator, causing it to leak.
Most cooling systems today are
designed to operate at 8 to 14 psi. If the radiator can't hold pressure,
your engine will overheat and lose coolant.
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 the 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.
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. But if the heater core is leaking (or a hose connection to the
heater core is leaking), coolant will be seeping out of the bottom of
the HVAC unit and dripping on the floor inside the passenger
compartment. Look for stains or wet spots on the bottom of the plastic
HVAC case, or on the passenger side floor.
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. Some engines such as General Motors 3.1L
and 3.4L V6 engines as well as 4.3L, 5.0L and 5.7L V8s are notorious
for leaky intake manifold gaskets. The intake manifold gaskets on these
engines are plastic and often fail at 50,000 to 80,000 miles. Other
troublesome applications include the intake manifold gaskets on Buick
3800 V6 and Ford 4.0L V6 engines.
INTERNAL COOLANT LEAKSThere
are the worst kind of coolant leaks for two reasons. One is that they
are impossible to see because they are hidden inside the engine. The
other is that internal coolant leaks can be very expensive to repair.
Bad
head gasket --Internal coolant leaks are most often due to a bad head
gasket. The head gasket may leak coolant into a cylinder, or into the
crankcase. Coolant leaks into the crankcase dilute the oil and can
damage the bearings in your engine. A head gasket leaking coolant into a
cylinder can foul the spark plug, and create a lot of white smoke in
the exhaust. Adding sealer to the cooling system may plug the leak if it
is not too bad, but eventually the head gasket will have to be
replaced.
If you suspect a head gasket leak, have the cooling
system pressure tested. If it fails to hold pressure, there is an
internal leak. A "block tester" can also be used to diagnose a leaky
head gasket. This device draws air from the cooling system into a
chamber that contains a special blue colored leak detection liquid.
Combustion gases will react with the liquid and cause it to change color
from blue to green if the head gasket is leaking.
Head gasket
failures are often the result of engine overheating (which may have
occurred because of a coolant leak elsewhere in the cooling system, a
bad thermostat, or an electric cooling fan not working). When the engine
overheats, thermal expansion can crush and damage portions of the head
gasket. This damaged areas may then start to leak combustion pressure
and/or coolant.
Cracked Head or Block -- Internal coolant leaks
can also occur if the cylinder head or engine block has a crack in a
cooling jacket. A combustion chamber leak in the cylinder head or block
will leak coolant into the cylinder. This dilutes the oil on the
cylinder walls and can damage the piston and rings. If the coolant
contains silicates (conventional green antifreeze), it can also foul the
oxygen sensor and catalytic converter. If enough coolant leaks into the
cylinder (as when the engine is sitting overnight), it may even
hydro-lock the engine and prevent it from cranking when you try to start
it. Internal leaks such as these can be diagnosed by pressure testing
the cooling system or using a block checker.
A coolant leak into
the crankcase is also bad news because it can damage the bearings.
Coolant leaking into the crankcase will make the oil level on the
dipstick appear to be higher than normal. The oil may also appear
frothy, muddy or discolored because of the coolant contamination.
Leaky
ATF oil cooler -- Internal coolant leakage can also occur in the
automatic transmission fluid oil cooler inside the radiator. On most
vehicles with automatic transmissions, ATF is routed through an oil
cooler inside the radiator. If the tubing leaks, coolant can enter the
transmission lines, contaminate the fluid and ruin the transmission. Red
or brown drops of oil in the coolant would be a symptom of such a leak.
Because the oil cooler is inside the radiator, the radiator must be
replaced to eliminate the problem. The transmission fluid should also be
changed.
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