Question about 1998 Oldsmobile 88

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Loosing coolant no visible leaks about 1/2 gallon every 100 miles

Posted by inyo2chuck on


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ZJ Limited

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How To Find & Fix Coolant Leaks

Loosing coolant no visible leaks about 1/2 gallon - 861e67b.gif

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.

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.


Posted on Mar 12, 2010

  • ZJ Limited
    ZJ Limited Mar 12, 2010



    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.


    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.


    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.


    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.


    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.


    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.


    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.


    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

    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.


    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.

  • ZJ Limited
    ZJ Limited Jul 01, 2010

    HERE can find other way to check the GM Bonneville 88 / LeSabre 1986-1999
    Intake Manifold

    Good luck.



Shawn Lane

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  • 46 Answers

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.

Posted on Oct 06, 2012



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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.

Posted on Jul 01, 2010


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Water pump is leaking as you go dwn the road and evaporating on the motor as it heats up

Posted on Nov 06, 2010

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