Thread: 2004 Grand Prix GT Slow Coolant Leak SOMEHWERE

Intake gaskets.

Its eating the coolant slowly.

Its a 2004 with the factory black plastic intake gaskets that fail, its a very common issue and with 120k you are well over do for a change on those gaskets.

The new aluminum gaskets stop the the issue of losing coolant.

I'd be surprised if he made it to 120k with the plastic intake gaskets.
Mine is an L32, but I HAD to change them at 45k.

OP, if you've never changed intake gaskets...now would be a good time.

How's the water pump? Remove the pulley and turn it by hand. Does it free wheel long after you turn it?
Replacing the coolant elbows with aluminum units would be more possible leaking plastic material taken out of consideration.

Originally Posted by GrandPrix666

How can I be certain on that or check it? The car doesn't overheat at all

Have you had to add coolant? If so, how often?

Originally Posted by Fivefingerdeathpunch

Its a 2004 with the factory black plastic intake gaskets that fail, its a very common issue and with 120k you are well over do for a change on those gaskets.

The new aluminum gaskets stop the the issue of losing coolant.

This. I would replace those intake gaskets even if they arn't the problem right now because eventually they will be. Also check the weep hole on the water pump (check for play in the water pump pulley also), check the two coolant elbows (may just want to replace them right away with aluminum ones as they will eventually fail too).

Check coolant reservoir for any leaks, the return hose for the reservoir.

Start there, you'll probably fix your problem.

Can I throw a theory out and see what you all think? As we all know, the intake gasket is a weak link. It was my understanding that they were recalled and the dealer used some sort of stop leak. You don't think when we change out the orange and flush we get rid of the "stop leak" ability?
Out of three 3.8 and one 3.1, I have had two intake gaskets leaks.
I bought 2 2002 Grand Prix with 20,000 about a year apart (one was early 02, and the other later 02).
One was a 3.8GT and the other was the 3.1SE.
Then I had a 99 3.8GT that had 70,000 and my daughter drove it through college, her husband traded off and I am not sure how many mile it had, but they had not problems, but I never touched the coolant in that car either for water pump or nothing.
The 02 GT, I got rid of it around 240,000 and the only other coolant issues is about 4 water pumps and the plastic elbows.
The other 02 SE3.1, I put a intake gasket on it about 60,000 and one water pump. It has about 240,000 and for a while I have been loosing coolant with no trace except for having to add some every now and then. Now I have some seeping between the block and intake. I bet it was going out the exhaust I was not seeing anything in the oil. I am getting ready to send it to the auction, I just bought a 07 GXP last week.
My fourth Grand Prix is a 06 GT3.8. I bought it was about 55,000 now has 158,000. I have not had any leaks, except one water pump. I have flush it once.
Then the 5th Grand Prix as mention is an 07 GXP just recently bought with 46,000 miles. Too new for any history yet.

Originally Posted by GrandPrix666

When I got under the car I saw there was definitely a leak coming from somewhere

Antifreeze does not evaporate like water. Do you have access to air hose. If you could blow off all the puddles, then see where it comes back from. I think it goes without saying to be careful of moving parts if you do it while the car is running. Another options is rinsing it off good at the carwash and really if there is not any grease just a water hose will do it. Clear water will carry off the antifreeze, then evaporate leaving only the new antifreeze.

As I said, my 02 GT leak for a while before the plastic elbow let go. I was adding about the same or once a month and I could get a whiff of antifreeze but could not find it. Also, it still could be the intake gasket, running to the bottom of the car. Watch real close between the intake and head. Also, it could be early enough that the leak is coming and going, even though you check once, look again at the water pump.
With almost 600,000 miles in Grand Prixs, these are the only areas I have had issues with, not saying it can't be something else, just looking at the odds.

could be the coolant elbows, could be the intake gaskets....pressure test the cooling system

While the plastic gaskets are a weak link, I've seen many achieve close to 200K and sometimes the gaskets still look good. However they are an issue and likely if you change them out etc, you'll clear up any issues you have going on.

Dads monte lasted 305k without changing them

I just got my coolant leak cleared up in my 98 gtp. Here's what I learned from it.

1. Trust what the guys on here have to say
2. Use an inspection mirror to try and find the leak on the underside of things.

Is there coolant being flung up onto your hood from your belt?

start feeling around all of your pullies to find how "high" the leak is.

My leak was a bad waterpump, so I had coolant dripping onto my crank. I could reach under the pump and find coolant. After that was cleared up, I then had an O-ring on a coolant elbow fail.

Coolant leaks tend to be pretty simple fixes, just gotta find where it's coming from. Try what I listed above and let us know.

Here is my suggestion like everyone else.

Lower Intake Manifold gaskets with new revised aluminum gaskets. There is a write up on here how to do it at home with a basic socket set.

While you are there you will have to change out coolant elbows which is also a known issue. Dorman has some newly revised aluminum elbows instead of plastic. Get yourself a set of those.

Make sure you do an oil change right after you put the gaskets on. Some run it for a bit then replace the oil.... a bit as in couple of minutes.


The way I see it you can spend ~$100 dollars now to be sure that your engine internals will be okay.

If the leak is exterior... it will be cheaper than buying a whole new engine. I replaced mine at 80k, and they still looked fine slight deterioration... but I did it for a peace of mind.