Pontiac Grand Prix Water Leak

kencollins · October 2011

I am pleasantly surprised to view your post (gmcustsvc), I will consult J.R. Pontiac-GMC in Tampa, Fl this week, explain the issue, schedule repair, then update you on the resolution.
Thank you very much for the concern expressed. Otherwise, I love the GXP Grand Prix. :shades:

dgriffin123 · January 2012

Is this for the front or rear passenger floor? My rear passenger floor is always completely soaked, as well as my trunk.

kencollins · February 2012

My water leak is not on the floor, it is on the roof (inside) between the sunroof and the door (at the top). Other people have indicated that the sunroof has a drain that has become clogged. I am not able to locate this drain and now the entire roof (the ceiling, just above my head) has become stained and now smells like mold and mildew and needs to be replaced.

Thanks
Ken Collins

gmcustsvcsarah · February 2012

Is this something you have already worked with a dealership to address? If we can be of assistance, please let us know!
Sarah
GM Customer Service

montana_cat · February 2012

Hi,

Has anyone experienced water filling up the area where the spare tire lays in the trunk? I have a 1999 Grand Prix GT and discovered the water in there last week.

The temperatures were below freezing and the tire was frozen in place in the area where it lays under the panel. Once my dad got the ice melted with a hair dryer, he had to bale the water out of the hole. It would have made a good fish bowl.

We kept a fan in it all day and also had to remove all of the carpet because it was soaked.

On a separate issue which led to finding the leak, I had to have my gas door replaced because one hinge had rusted away and the other was getting close. So the man who did my body work checked the trunk for leaks while he had my car and couldn't find any. He actually laid in the trunk while someone sprayed water all around the trunk, lights, spoiler, etc. and it did not leak.

So, we have no idea where this water is coming from.

Does anyone have any experience with this or any ideas?

emarker · March 2012

I haven't had any leaks, but I think water got to my a/c harnes. How do I fix the water leak under the front cowl BEFORE the leak starts?

Thank you,

Eric

leahrae · May 2012

I have a 97 Grand Prix and recently noticed after a two hour drive (running the A/C) we noticed quite a bit of water on rear floor. It was not raining nor had it been. When we stopped the car, we noticed that under the car stream of water coming from just behind the front door. There is a seam there and it is just about in the same area as the back floor board. This happended one time before -same trip but we thought grand nephews poured water on floor board-now not so sure. noone was around. Where can this water be coming from?

baba14 · June 2013

Anyone out there that can help with my leaking car. I have a Pontiac grandam 2004, every time when it rain I got puddle of water on the floor on the passenger,s side. I thought it was because on the right side of the windshield molding was missing, so I got that fixed but that didn't help. My car is still leaking. Again this morning my car was out in the lot in heavy rain, went to see if there was water, yeah, about 2" of water on the floor. This is been going on for about 2 weeks now. The leakage started about 2 weeks ago. I am tired of vacuuming the water out when every time it rain. However, it happen I was sitting in the car while it was pouring rain again, then I saw water was dripping from the fuse compartment and between the passenger's door. The water was dripping from the fuse box, down to speaker on the door and on to the floor. I just can't find where the water is sipping through. The door is shut tight and the window. But is still leaking. Please help!!!

klinaweaver · July 2013

im having the same problem, with my spare tire swimming in my trunk! i opened the back seat and had someone spray all the cracks around my trunk, no water, but when i had someone spray UNDER my car, thats when the water seemed slowly to trickle in. did you ever find anything on the issue?

charlie28t · May 2014

When I bought this car with only 40,000 miles on it the first issue I ever had with it was when water started pouring out the back reading light on the driver side rear. I immediately took it in and they said a hose had just gotten loose and they fixed it. Here it is now 80,000 miles and not only is water coming pouring out the same light fixture , but also has escalated to come out where the roof meet the front driver side . My entire driver side roof is soaked , my seats, my floorboard , and now my new to me car is smelling of mold just like ever other car I have ever own. You have NO IDEA how that fact depresses me more then anything. If this is a well known error why hasnt there been some sort of recall. To fix the "hose falling off " issue.. I am not a mechanic so the idea of ripping my headliner down to try and fix this problem myself is not really a solution. Nor do I feel that a well known issue as this should be something I should be paying outlandish mechanic fees to just get fixed for what another 40,000 miles? This is ridiculous!

thumper14 · October 2015

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

imidazol97 · 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?

thumper14 · November 2015

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_Flyer · November 2015

Something wrong with the heater core? You've eliminated an awful lot of the rest.

Mr_Shiftright · November 2015

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.

imidazol97 · November 2015

@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.

Pontiac Grand Prix Water Leak

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