Frustrating Coolant Leak - 99 Grand Am - V6 3.4L

Hello board! I’ve been listening to CarTalk for a bit over two years since discovering it on the WHYY/NPR stations in Philadelphia and have found the advice meted out invaluable and hilariously enlightening. I finally come online to the community to ask for your expertise in helping track down the source of a vexing engine coolant leak that has been a thorn in my side for a month and a half. Any help or direction is greatly appreciated. Here’s the story:

I own a 1999 Pontiac Grand AM SE (v6 3.4L). It was a generous gift given to me a by a family member who unfortunately can no longer drive. The vehicle had been involved in a flood (which reached the engine and steering wheel) in the earlier part of 2000, but the insurance company refused to junk the vehicle. I took possession of it two years ago and it has been nothing but a headache since. Recently, I developed several problems with my cooling system. In October, i suffered overheating and coolant loss that was traced to a cracked sidewall in the original radiator. I suffered through the cost of replacing the radiator and at the same time decided to replace the upper and lower radiator hoses and the reservoir and overflow hoses as well. All was fine until January when I experienced a plume of white smoke coming from my engine while driving down the road.

At first I thought the smoke was a blown gasket. However, after the smoke reached the cabin, it smelled sweet. I pulled over and noticed that my lower heat core hose connector had completely severed in half. Having been on my way to work, and unable to repair it myself due to the urgent need to have it repaired ASAP, I had it towed to Pepboys. I knew exactly what was wrong and instructed them to replace the connector, the clamps, and the lower heater core hose. They did a pressure and dye test on the coolant while repairing the issue and was unable to see any other leaks. The pressure test remained steady for 30 minutes during testing after the repair and a top off of my coolant. The second I drove it off of the lot I started to smell antifreeze when running my heater. At first I thought it was residue burning off from the failure. I let it go for a few days but noticed that my reservoir was completely empty (even though my vehicle was not indicating an overheat or moving much off of center line). I could not see antifreeze markings at the overflow spout or a leak coming from anywhere. I added more fluid but the coolant kept leaking from somewhere. I called Pepboys back and they took a look at the work they had done.

They said they inadvertently used a bent heater core hose instead of a straight one which was causing a kink and overpressure in the system. The connector they had placed was showing a leak during the pressure test. They replaced the hose with the correct one and replaced the connector again under original labor warranty. Once again they pressure tested the system with a dye and no leaks!

I drove off… but three days later noticed I was starting to line over center for engine heat and could still smell antifreeze when running my heat. What’s worse is that I could smell antifreeze outside of the car while it was running now and antifreeze when running cold air as well. I still had a leak somewhere! I contacted Pepboys again. They took the vehicle back and told me that this time the upper heater core hose connector was leaking! Rather than argue, I had them fix it, this time at additional cost to me. Furthermore, they used Ford connectors for my GM and said it would not be an issue. This was three days ago.

I’ve been starting to push beyond half for engine temperature the past day and pulled my coolant cap and noticed my reservoir was completely empty! As far as I can tell there is no crack in the reservoir. I am still leaking from somewhere. I have heat so I do not believe it’s an air bubble trapped in my system. I also do not think my heater core is leaking as I have strong heat in the car. I further do not believe it is a manifold or gasket leak because I have constant power and steady RPM, no sputtering or white smoke from the tailpipe, and as far as I can tell, no mixing of oil and coolant.

Is it possible I am still leaking from these supposedly repaired FORD connectors or could there be another problem in the system where I am leaking from that would not show up on a pressure test?

I’ve put a lot of money into this car, especially on the coolant system recently, and Pepboys has been unable to tell me anything besides their believe it’s the connectors…two of them… within two weeks of each other…

Any ideas?

Once again, thanks!

GM V6 engines are notorious for failed intake gaskets

When that happens, coolant can get into the crankcase

That may be why your coolant level is low, yet you can’t see the leak

Just something to keep in mind . . .

I think your heater core is toast.


You may well be right

I wonder why OP didn’t mention any visible coolant leak in the cabin

There’s only so much the carpeting can soak up

The reason I suggested the intake gaskets is because OP says he constantly has to refill coolant

Perhaps the coolant is sloshing around in the heater case . . .

The first idea I can come up with is to find a local independent repair shop instead of the big chain stores. A half hour pressure test isn’t long enough in my opinion. When working on cooling systems, I always pressure test for at least two hours. Have we checked the oil to make sure there’s no intermix of coolant and oil ?

That “sweet” or “stale curry” smell is nearly always a leaking heater core. Especially if the windshield fogs up. Have that checked out first.

I think the Pepboys guys are blowing smoke with that “bent heater core hose” excuse.
I also think they never turned the heat on when they purged the system, preventing the coolant from going through the heater core and preventing the core from purging. That may also be why the passenger’s floor isn’t flooded.

At this point, I’d start by checking both the intake manifold and the ability of the cylinders to hold pressure. That’d either identify or eliminate the intake manifold gaskets and the headgaskets as being the cause.

I’m guessing the OP will have his answer by then, but if not I’d purge and refill the cooling system (with the heating system on), and try chasing the leak with a UV sensitive dye kit, available from any parts store. IMHO the water pump would be suspect, as it may only be leaking when the engine is running and the shaft spinning, making it immune to a pressure test, but I would not make any assumptions.

To purge the system, elevate the front end so that the radiator fill hole is the highest point, fill the system as full as possible, then start the engine, turn the heater on, and keep filling while the system warms up some. When you’re confident that the T-stat has begun to open, you can install the radiator cap, fill the reservoir, let it warm to operating temperature then cool, and refill the reservoir. Check it a few times in the coming days.

It sounds to me like Pep Boys are doing a decent job of treating the symptoms, with out actually finding the cause. It sounds to me like your cooling system is building up too much pressure. A simple test you can do your self, fill up your coolant to the normal level, leave off the cap from your radiator, and start the car. Wait for the car to get good and warm, and watch it. If it slowly bubbles over a little keep at it. If it strongly boils over…sell the car.

Could it be the heater core? I was told they left the heat running with the radiator cap off for over half an hour when they replaced the connectors (both times) and refilled the coolant. What they said and what they did though could be two different things lol!

I haven’t noticed any coolant entering the cabin and the carpets are dry as a bone. Does that preclude the possibility of a leak? You’re the experts and I’d guess not, but doesn’t a leaky heater core usually manifest with soaked carpets, especially if the system was properly purged? Also, the windshields do not fog up with vaporized coolant when using the heater/defroster. It’s just a slight smell I can sometimes notice which I was told was probably residual coolant which made it into my vent system after the original blowout and could take a bit to cycle out. To me it doesn’t seem like residual left over though.

I’ve thought about the possibility of it being a leaky/blown intake manifold gasket. The compression test that was run came back OK and indicated no problem though. Do I need to have the engine vacuum tested now, even with a smooth idle? Would that point toward something the compression test might not have caught?

I also don’t seem to have most of the common symptoms of a traditional manifold leak but don’t preclude that as being a possibility. I do not have sluggish acceleration and my fuel economy has stayed pretty much consistent over the year (crappy for this v6). My idle is steady and I can’t ‘hear’ any hissing or slurping/gulping or whistling when the vehicle is idling. I also don’t appear (but it could be a possibility) to have any mixing of coolant and engine oil. The test strips haven’t indicated cross-contamination and the color and smell of the oil hasn’t changed. There is also no coolant puddle under the vehicle after it is driven for distance, turned off, and parked for hours. There is also no steaming from the engine I can detect.

I’ve had the system UV dye tested three times now and as far as the mechanics have said, they don’t see a leak anywhere except those connectors which were replaced. I will have the system pressure and UV dye tested at another family mechanic this time. hopefully with more time he’ll be able to track down what is causing me to lose coolant.

I’m going to try to repurge the system with the instructions you provided mountainbike :). You’re saying if the heater core is the culprit and I properly purge the system, that it MAY manifest by leaking into the carpet? Can I perform that purge without dropping the existing coolant? Can I just bleed the system or will i need to completely flush and refill?

Thank you a;ll for all of your great advice!

I’ve seen plenty of manifold gaskets leaking, which don’t always produce that hissing sound

Yet the crankcase fills with coolant, all the same

Pull the dipstick
What color is the oil?
Is it high?
Does it look like coffee?

Take a peek in the coolant surge tank
What does it look like in there?
Looks like milkshake?

Drain some engine oil into a small tub
Looks like coffee or milkshake?

Yes, if the heater core were leaking and were purged it would likely leak to the carpet, but with this additional information I no longer suspect that as a problem. I was unaware of all the work that had been done. And I don’t think another UV dye test will help you.

That compression test that was run, do you know how it was done? The test I was thinking of is called a “leakdown test”, or sometimes a “compression leakdown test”. The way that’s done is by putting a fixture in the sparkplug hole that allows air to be pumped into the cylinder, the air input to be shut off, and the pressure in the cylinder to be monitored. If the pressure drops beyond a specified amount, it suggests that the air is passing through a breech in the headgasket.

A bad headgasket can also be confirmed by using a lab strip to check the coolant for the presence of hydrocarbons, and often bubbles will be seen at the radiator fill hole as the engine runs and the combustion gasses are blown into the water jacket and migrate up to the fill hole.

First, however, follow Db’s suggestions.
Second, I’d suggest a leakdown test.

I haven’t had the time (or $$) this week to drop it off a recommended family mechanic yet. I did however have two small updates regarding the problem(s).

First: I discovered that my radiator fans are not working when the engine temperature climbs past half toward 3/4 on the gauge. I was starting to run hot while idling in traffic and decided to get out and check the radiator at which time I noticed the fans were not running. However, the fans do have power to them. When I turn on the A/C the fans engage and come on. I had to turn on the air conditioning to cool the vehicle down and force the fans to run. I suspect I may have a bad coolant temperature sensor. Thoughts?

Second: I discovered amber brown, sticky, wet residue on the radiator hoses (brand new) on the passenger side of the vehicle directly in front of the A/C compressor pulley and in front of and below the water pump pulley. At first I thought it was the water pump I was looking at, but a diagram showed that it was the A/C portion. Can clearly see that the wet spots and residue on the hoses line up with where the pulley rotates while running. I can also see that the engine is wet underneath of the bottom pulley where they attach to the engine. I’ve included two pictures to visualize what I am talking about. Even though the hoses are wet in front of the A/C pulley, could I have a leaking waterpump? I didn’t notice any wetness on the serpentine itself. Could it be something else? Can you lose coolant if your A/C compressor connections are leaking? Is there a gasket around that location which could be the cause of the leak as well? I really think this is the primary reason why I continue to lose coolant. Based on the location what do you all think?

Pics attached.

Thanks for the continue support and info!

I almost forgot to mention, as this may be of some importance?

About two weeks ago, I noticed what sounded like a whirring or a whining coming from the pulley assembly. It’s intermittent at best, sometimes it gets louder when idling, sometimes there is no sound, and sometimes it won’t go away. I thought about the possibility of a bad bearing in one of the pulleys, or possibility of a bad bearing in the alternator or some other area like the water pump. I haven’t yet had it manually cranked, but given what I just posted about the location of the leak, does that possibly narrow down the location of the coolant loss?