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 LEAKS
There
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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PRESSURE TESTING THE COOLING SYSTEM
There are several ways to find out whether or not your cooling system is
holding pressure. One is to top off your cooling system, tighten the
radiator cap and start the engine. When the engine reaches normal
operating temperature, turn on the air conditioner (to increase the
cooling load on the system) and/or take it for a short drive. Then check
the radiator, hoses and water pump for seepage or leaks.
WARNING: DO NOT open the radiator cap while the engine is hot! Even if
the cooling system is leaking, the coolant will be under considerable
pressure -- especially if it is low and coolant is boiling inside the
engine. Shut the engine off and let it sit about an hour so it can cool
down. Then place a rag over the radiator cap and slowly turn the cap
until it starts to release pressure. Wait until all the pressure has
vented before turning the cap the rest of the way off.
A special tool called a pressure tester can also be used to check your
cooling system. The tool is nothing more than a little hand pump with a
combination vacuum-pressure gauge and a fitting that is attached to the
radiator filler neck. To check for leaks, attach the tool to the
radiator and pressurize the radiator to the pressure rating on the
radiator cap. For example, if you have a radiator cap that says 12
pounds, you pressurize the radiator to 12 lbs. and wait to see what
happens. If there are no leaks, the system should hold pressure for 10
to 15 minutes. If it does not hold pressure, the system is leaking. If
you cannot see any visible leaks on the outside, it means the leak is
inside (bad head gasket or cracked head or block).
A block Checker is another tool that can be used to detect a leaky head
gasket. The gas-sensitive blue liquid changes color if there are any
combustion gases in the coolant.
Leak detection dye can also be added to the coolant itself to make a
slow leak easier to find. Some of these dyes glow bright green or yellow
when exposed to ultraviolet light.
RADIATOR CAP CHECKS
The radiator cap should also be pressure tested, especially if the
system has been overheating or losing coolant with no obvious external
leaks. A weak cap that cannot hold pressure will allow the system to
boil over. If the cap cannot hold its rated pressure, replace it.
RADIATOR REPAIRS
If your radiator is leaking, you have several repair options:
You can try the cheap fix and add a bottle of cooling system sealer to
the radiator. These products are designed to seal small leaks. They can
also seal internal engine leaks. Some work better than others, but most
provide only a temporary solution to your problem.
You can attempt to repair the radiator yourself. Copper/brass radiators
on older vehicles can often be soldered to repair leaks. Cracks or
pinholes in aluminum radiators in newer vehicles can often be repaired
with epoxy glue. But if the core is severely corroded or damaged, the
radiator may have to be professionally repaired at a radiator shop, or
replaced with a new radiator.
FIXING A LEAKY HEATER CORE
As with a leaky radiator, you might try the cheap fix and add a bottle
of cooling system sealer to see if that will stop the leak. If it does
not, you will have to disassemble the HVAC case to replace the heater
core. This is a nasty job and involves a LOT of labor on most vehicles.
If a vehicle has a history of repeat heater core failures (some Chrysler
cars, for example), the problem may be electrolysis corroding the
heater core. One fix is to attach a grounding ******** the heater core.
Another is to replace the OEM aluminum heater core with an aftermarket
copper/brass heater core.
COOLANT RESERVOIR
Another coolant component that sometimes needs attention is the coolant
overflow reservoir. The coolant overflow reservoir does more than catch
the overflow from the radiator. It serves as a storage tank for excess
coolant. When the system is hot, coolant will be forced out through the
radiator pressure cap and into the reservoir. Then as the system cools
down, decreasing pressure will draw coolant back into the radiator.
On many newer vehicles, the coolant reservoir is pressurized and is an
integral part of the cooling system. The filler cap for the cooling
system is located on the reservoir tank, and the tank is connected to
the radiator and engine with hoses. The reservoir is transparent plastic
and you can see the coolant level inside.
If the coolant reservoir is cracked or leaking, the system may lose
coolant every time the engine heats up. Eventually, this can cause the
engine to overheat.
Small punctures or cracks in the overflow reservoir can usually be
repaired with silicone glue. If the reservoir needs to be replaced, make
sure the hoses are routed correctly between the radiator and the
reservoir, and that it is free from kinks that could block the flow of
coolant back and forth.
FIXING LEAKY FREEZE PLUG
There are several ways to repair a leaky freeze plug.
One is to clean the surface of the plug, then sand it lightly with
sandpaper, and pack it solid with a high temperature two-part epoxy such
as gas tank sealer. Let it cure overnight. This trick usually seals
leaky expansion plugs that would otherwise be very difficult to replace.
Another is to use a hammer and drift to knock out the old plug. Pounding
in on one side of the plug will usually cause it to twist. The plug can
then be pried out with a large screwdriver. Clean the hole, then apply a
liberal coating of sealer to the hole and carefully drive in a new
replacement plug. The plug must go in straight or it may not seal.
Another option is to install a repair plug that has an expandable rubber
grommet to seal the hole. You simply place the plug in the hole and
tighten the bolt until it seals tight.
FIXING LEAKY HOSES
Do not waste your time trying to patch or wrap a leaky radiator or
heater hose. Sealers do not work well with hoses either. Replace the bad
hose with a new one, and inspect all the other hoses because if one has
failed the others are probably reaching the end of the road, too. It is
also a good idea to replace the original hose clamps, especially if
they are the ring type. Ring clamps can lose tension with age and may
not hold the hose tightly. Worm drive stainless steel clamps are best.
FIXING A LEAKY WATER PUMP
No stop leak will seal a water pump that's losing coolant past the shaft
seal. Replacement is your only option here. But you can save some money
on the job by using a remanufactured rather than a new pump.
Replacing a water pump is not too hard a job on most engines, but on
some it can be tricky. On 2.8L GM V6 engines, for example, the bolts
that hold the water pump also hold the timing cover in place. If you are
not careful, the timing cover seal can be broken allowing coolant to
leak into the crankcase. GM recommends using a special tool (J-29176 or
equivalent) to hold the timing cover tight while the pump is being
changed.
If your engine has a belt-driven fan with a fan clutch, it is also a
good idea to check the fan clutch when replacing the water pump. The
lifespan of both is about the same, so the fan clutch may also need be
replaced. If the clutch is leaking silicone fluid, or has any wobble in
the bearing, it must be replaced.
REFILLING THE COOLING SYSTEM
When refilling the cooling system after making a repair, always use a
50/50 mixture of antifreeze and water. Never use straight water because
it has no freezing protection, no corrosion protection and it boils at a
lower temperature (212 degrees F.) than a mixture of antifreeze and
water (which protects to 240 degrees F.).
On some late model front-wheel drive cars, refilling the cooling system
can be tricky unless you "burp" the system by opening a bleeder vent or
cracking a hose at a high point in the system to allow trapped air to
escape. If you do not get all of the air out, the engine may overheat
the first time you drive it.
The best way to refill the system is to add coolant until the radiator
is within an inch of being full. Also add coolant to the coolant
reservoir, filling it to the proper level. If the system has a
pressurized coolant reservoir, add coolant until the level inside the
reservoir is at the COLD FULL mark. Start the engine and let it idle
with the radiator or coolant reservoir cap off until the thermostat
opens and coolant starts to circulate through the engine. The heater
should also be on so coolant will flow through the heater core. As the
coolant level drops, continue to add coolant until the system takes no
more. Then replace the radiator cap and drive a short distance. Shut the
engine off, and after it has cooled recheck the coolant level once
again. If low, add as needed.
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Did they perform a cooling system pressure test as well, and what was the result of that? If the dye didn't show any external leaks, did they analyze the exhaust as well for any traces of coolant?
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