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Pontiac Grand Prix Water Leak

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  • My son has a 2003 Pontiac Grand Prix GT. He was having problems with it overheating, coolant leaking, etc. He took it to two garages and spent a lot of money. Now the car runs fine but he has no heat. The heater just blows cold air as does the defroster. He has a sloshing sound from water on the passenger side floorboard. When he has notice that it's going to rain, he puts a tarp over the windshield and that helps with the water on the floorboard. It also helps if he pulls in his driveway instead of backing in because his driveway is at a slant. He's had the radiator flushed, thermostat and the water pump replaced. Air conditioner works fine. Everyone says he needs a new heater core or his head gasket is blown. I believe that leak is the problem. Is there an easy way to find out if his head gasket is blown or if it is the heater core? Don't have money to spend on things that aren't broken and I've read a lot about the leaks. Thanks
  • imidazol97imidazol97 Crossroads of America: I70 & I75 nee US 25 & US 40Posts: 19,800
    edited October 2015
    Several possible problems. Is the water that's sloshing actually on the floor or are you hearing water moving around inside the heater/AC case? You may have a drain tube stopped up that keeps the water from the AC from draining out: it builds up and you hear the slosh and it runs out between seams onto the carpet. Drain tube is near center right of firewall behind engine. Must have car up on proper safe hoist.

    Does the car fog the windshield easily? A symptom of water inside the case from either AC water or heater leaking. BUT a heater leak smells like hot coolant, not just musty water.

    Have a sunroof?
    You have may a tube for the sunroof leaking? On Bonnevilles, they occasionally came off where they go through the floor board and the water from the roof drains into the cabin in the carpet area. The front tubes go down through the A-pillars and penetrate the floor. Must remove the carpet and rubber underlayment to get at the problem area. That might explain why parking uphill so the water around sunroof flows more to the back drains seems to help.

    If you are losing coolant, it could be the gaskets between the lower intake manifold--I assume this is a 3800 engine--and the tops of the heads. These are usually replaced along with the upper intake manifold which is plastic and can also leak coolant into the engine near the throttle body. Does your oil on the dipstick show a brown color sort of milkshake like?
  • Water was sloshing on the floor. Floor was extremely wet. Oil is fine. Put sealant around the windshield as everyone suggested and that stopped the leak. No more sloshing water. Sun roof is not leaking. As I said the car runs fine, air conditioner works, air blows from heater and defroster but it's cold. Not just miserable riding in cold car but can't see out the windshield without the defroster. The leak has been fixed; new water pump, no over heating, The car is not losing coolant. The radiator has been flushed twice and the tube was flushed.What's left? I have to have heat and a defroster that doesn't blow cold air.
  • PF_FlyerPF_Flyer Pennsylvania Furnace, PAPosts: 6,766
    Something wrong with the heater core? You've eliminated an awful lot of the rest.

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  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 49,907
    You might have to bleed the cooling system. This is usually done by running the engine with the cap off and letting the system "burp" the air out, then adding coolant as necessary. If the coolant wasn't installed properly to begin with, this is what could happen.

    Other than that, you can feel the inlet and outlet heater hoses from the engine compartment. If one is warm but the other cold, then you may have a heater valve issue. If both are hot, and there's no air blockages, I'd have to say that you have a stuck blend door under the dash or one helluva clogged heater core.
    thumper14 said:

    Water was sloshing on the floor. Floor was extremely wet. Oil is fine. Put sealant around the windshield as everyone suggested and that stopped the leak. No more sloshing water. Sun roof is not leaking. As I said the car runs fine, air conditioner works, air blows from heater and defroster but it's cold. Not just miserable riding in cold car but can't see out the windshield without the defroster. The leak has been fixed; new water pump, no over heating, The car is not losing coolant. The radiator has been flushed twice and the tube was flushed.What's left? I have to have heat and a defroster that doesn't blow cold air.

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  • imidazol97imidazol97 Crossroads of America: I70 & I75 nee US 25 & US 40Posts: 19,800
    @thumper14 says, " the tube was flushed."

    What tube do you mean?

    Let's do some "if's":

    With the engine warm and the front of the car uphill on a driveway if possible, run the engine at 2500 rpm for 10 seconds or so, then idle, then repeat 4 more times. This will help move air from the heater core if it has been trapped there. Usually high engine rpms on the road will burp that air out, but maybe not in your case.

    Feel the upper radiator hose after the car has been idling for 15 minutes or driven. It should be so hot you can't hold it barehanded. If it's not warm, let the car sit for hours. Then restart and keep feeling the upper radiator hose for hot water to start through it gradually. The thermostat might be opening too soon in that case. There should be almost no heating of the middle of that hose until all of a sudden the thermostat opens and the engine has reached 195 deg. F.

    If the car is warm after driving for 15 minutes or more and the blower on the heater on low, feel both tubes to the heater core near the firewall.
    Be careful of the moving belts and any loose clothing. Both should be very warm

    If both are warm, turn the blower on high and wait a minute or two and feel again. The one tube should be cooler than the other but still warm. That's the return tube. The air flow through the heater takes heat from the water so the returning water is cool but not cold. You can have someone idle the engine at about 1500 and recheck.

    If one is essentially cool and the other is warm, you likely have a clogged heater core with no flow.

    If the system had DexCool in it that had been contaminated with other coolants when you started having these problem, the core may be clogged by that. If the car didn't have good maintenance, the DexCool may just have coagulated and clogged it. A reverse flush on the heater core may help open it some, and it may easily clog again.

    A few may be able to use some cleaning chemical that will open it, but don't bet the bank on that. The typical flush the garages like to do to clear the radiator usually don't work on the heater core in these.

    Replacement of heater core may be needed.
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