How To Find &
Fix Coolant Leaks
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.
Hope help with this.
HERE can find other way to check the GM Bonneville 88 / LeSabre 1986-1999
Intake Manifold
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Check each spark-plug. White coating indicates you are burning antifreeze check oil for signs of water, and check coolant for signs of oil . Loss of power and/or stalling usually indicates plugged catalytic converter(s). Bad head gasket(s) can be replaced. Cracks between valve seats are common. YOU CAN FIX THIS ! but not by welding. You must disassemble the head completely (including frost plug). Then clean it ABSOLUTELY clean.
There are engine shops to do this. Then find the crack . Take a stick with a hunk of plasticene wrapped in saran wrap and poke it to exactly the spot of the crack. Push gently upwards to squish an imprint of the interior of the head where the crack is . Gently pull the stick and 'blob' down off the crack spot and out. Be sure to EXACTLY measure/mark how far the stick went in . Now get a small but appropriate size piece of aircraft aluminum and carve and beat it (on a piece of soft pine wood) to the shape of the imprint left on the plasticene. Now assemble the aluminum piece loosely (with a small blob of silicone for 'glue') onto another stick. Buy a tube of WATER-PUMP silicone ( the grey kind that hardens into something as tough as rubber-boot rubber THIS IS EXTREMELY IMPORTANT !!!) Put about a 1/4" to 3/8" thick layer on the matching side of the aircraft aluminum patch. Before adding silicone make DAMN sure the 'patch' fits as good as you can make it over the crack . A good 1/2" overlap of the patch around the crack is good. Now add the w p silicone layer on the patch and carefully get it to where it has to go. At the proper spot push gently the patch up against the head. DO NOT PUSH COMPLETELY TIGHT, METAL ON METAL. YOU MUST HAVE SILICONE BETWEEN THE PATCH AND THE HEAD. DO NOT SQUISH MOST OF IT OUT !!! To get a 'feel' for how much you can push the piece with the silicone before you ruin the job, you can experiment on a piece of junk. Now with the patch in place LEAVE EVERYTHING ALONE AND WITH HEAD UPSIDE DOWN FOR 3 DAYS IN A WARM PLACE. Then simply twist the stick slowly till ALL of it comes off and out. Your head should be sealed now. No coolant should flow out the crack anymore.
If the crack is old it will never get any bigger than what it was. This trick ONLY works with the silicone/rubber (waterpump kind) that hardens like boot rubber. If you squish too much 'guk' out from under the patch you risk clogging your head drain holes. And i must repeat, the head has to ABSOLUTELY, COMPLETELY FREE OF ALL GREASE, DIRT, ETC. for the 'guk' to stick properly.
I did this and fixed the cracked head (between no. 2 and no. 3 cylinder valve seats) on my 1988 mazda b2600 4x4 head.
This fix cost me $10. for 'guk' , nothing for the patch, $20. to clean the head, plus a new head gasket (?$) . I also 'fixed' the catalytic converter that was clogged.
The engine ran fine , once assembled, and i also reground the valves and seats. Until rust killed the whole truck it ran fine fine for 5 trouble-free years.
I saved $2600. (for a new head, unmachined, which incidently comes with the same weak fillet area between no.2 and no 3 cyls. )
I had this same issue not long ago, The water pump starts leaking but where the weep hole is it is very difficult to see, I went along a few months before it let go all the way.
The series 2 3.8 V6 is infamous for it's upper intake manifold failure. They warp around the egr port and leak coolant. For around $150 you can get the revised upper intake from the aftermarket.
Water pump is leaking as you go dwn the road and evaporating on the motor as it heats up
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