2004 Monte Carlo LS No Mods 85,000 Miles.
2G1WW12E549325366

I've put a gallon of Coolant in it this past month.

No visible leak.
No gunk on Oil Fill Cap or Dipstick
No smell

Obviously, a bad sign.
What else should I be looking for?

 

Besides puddles on the ground?

You have a 3.4... I would start saving up for the worst.

 

Perhaps, the dreaded lower intake manifold leak. But, I thought or recall reading somewhere, that 3400s made after '03 had a revised gasket and torque fasteners specs that somewhat resolve the original problem.

Anybody care to chime in, cause I have a 3400 and would like to know.

 

how long does it stay in? and theres not puddles? mine leaks some sort of fluid but i think its just water, i just filled my coolant before but i dont think the level has gone down at all

 

Head gasket or intake gasket....

 

I know that when the LIM in my moms 2000 Bonneville 3800 was leaking, the dealer said when they fixed it they used a revised gasket/ fasteners. We got it fixed in 2006.

So obviously GM was well aware of the problem then. I think your right, I THINK I read somewhere that they started this "fix" for the issue in 2005, but you might be right, maybe it was 2004. I don't know if the fix applied to the 3400, cause all my research was 3800 based. But i'm assuming they fixed the issue in all engines at the same time. (3100, 3400, 3800)

 

i marked mine off to make sure it isnt leaking, eventually it will lose some tho overtime right?

 

In no way does it sound as bad as your problem, but i had leaking antifreeze as well, no visible leak, and it leaked slow enough where i thought it was ok, and then my light would come on, and when i checked it, my tank was empty, and it was the dreaded intake gasket, one friggin steep bill later the dealership replaced my gasket but honestly, apparently the problem is the 50/50 coolant itself, it basically eats away at the gasket, i never heard of them fixing the problem but if you don't see any apparent leaks, i would go with chibiblacksheep and save up for the worst, maybe check the radiator though, idk, i know yours is the 3400, i got the 3800, but maybe the problems the same, i hate to be negative but just sharing the experience

 

wild what would you do then with the coolant?

 

After getting the new gasket, flush the cooling system completly, and replace with Prestone All Make All Models...Dexcool is crap IMO. I have done lots of research about the problem, and Dexcool has problems in a number of GM cars.

Its is correct that the Dexcool eats away at the gaskets...But from what I remeber when a dealer replaces the gasket, they use a different one, that has improved resistance to the Dexcool eating it...plus I kinda remember the mechanic telling me that it was common for the leak to start around the fasteners, so that is why they came up with an "improved" fastener set up...

If your car happens to be under warranty, keep Dexcool in it till warranty expires, but change it every 25-30K......