1999 Pontiac Grand Am 3.4 Liter Coolant Problem....

[bandit7862]

I am hoping to get some help on my Grand Am if anyone has had a similar problem. The problem is I am losing coolant at the tune of about 1/2 gallon a week and cannot find where it is going. I am pretty knowledgeable about cars but this one has me troubled. I know it cannot be blowing by the intake manifold because there is no coolant in the oil (thank God!). It is not leaking on the ground (maybe a little) but nothing significant. In the mornings when it is cold, I see a steam vapor out of the exhaust pipes for about five minutes before it is warmed up, and then it is cleared up. When it is fairly cold out, it starts fine, but spits and sputters like it wants to shut off and idles very rough. Once it is warm, it runs perfectly (with a smell of coolant at times). It cannot be a bad heater core because I am getting toasty hot heat inside and there is no wetness on the floor boards.
I have replaced the thermostat and water pump so far to no avail. Could this coolant be leaking out the exhaust manifold? Or the radiator while driving? Any advice or suggestions would be greatly appreciated. Thanks, Randy

[GTP Dad]

It could be a small leak in the heater core. The heater boxes have an outlet that will channel the antifreeze to the outside of the box and it will drop down behind the engine onto the ground. The outlet is usually on the passenger side. Start the car and let it run for a while with the heater turned on. Look under the car and see if there is any coolant on the ground. Also check the hose fittings when you start the car in the morning especially when it is cold. You could also have a loose hose clamp and the coolant is evaporating once the car warms up. Finally, if the coolant was leaking into the exhaust you would see a plume of white smoke that smelled like antifreeze.

[Airjer_]

If you look under the throttle body and on top of the transmission you will probably either see a pool of coolant or the dried up remnants. I wouldn't rule out the intake gaskets.

[bandit7862]

Originally Posted by Airjer_

If you look under the throttle body and on top of the transmission you will probably either see a pool of coolant or the dried up remnants. I wouldn't rule out the intake gaskets.

Thanks for your help, I am going to replace the intake manifold gaskets for starters and all the hoses.

[bandit7862]

I am right in the middle of changing out the intake manifold gaskets and was wondering if I need to place a very small bead of black RTV on the heads and then lay the gaskets in place? Then should I place another small bead of RTV on top of the gasket before setting the manifold in place? I know I have to use a large thick bead on the bottom valley on each side but wasn't sure if I need to use the RTV under and on top of the intake manifold gasket itself. I have all of the aluminum sealing surfaces cleaned on the heads and the manifold itself, so I am ready to install the gaskets.
My other question is if anyone has the exact torque specs for the rocker arm bolts and the intake manifold bolts? I know the manifold bolts are done in 3 stages to tighten but wasn't sure of the specific "in-lbs" settings for each stage. I have the Haynes manual, but would like some other info so that I can compare the numbers because these torque settings are extremely important that they are done exactly right. I do not want to take the chance of getting the torque wrong or I will be replacing these gaskets again in 6 months and these gaskets are not cheap.
Lastly, do you think I can use any type of cleaner as in brake fluid or something similar to clean out the build up of the black tar looking stuff inside the intake manifold ports and the head ports? Would this ruin my fuel injectors because when I took it all apart I did not remove the fuel injectors? I left the fuel injectors together with the intake manifold, but there is some black tar/gum build up inside a most of the ports. Would it cause any problems with the engine itself if I use any cleaner in these ports?
Thanks for any info on this matter.

[ampfreakin]

I have the exact same problem.I own a 1999 Grandam 3.4liter v6 automatic and it guzzles about 2liters a week , leaves no evidence of a leak on the ground ,none in the oil. It starts fine but runs rough at idle; rpms up and down almost quitting.I also own ,off the road now,a 1995 Grandam 3.1liter v6 automatic.It used to do the same thing and the problem was a headgasket,which had a small tear between a coolant passage hole and the cylinder bore hole.It was the no.1 cylinder. The reason you dont see any coolant is that its sucked into the cylinder first then of course goes out the tail pipe while your driving.I did the work myself ,new headgaskets,lower and upper intake manifoldgaskets and though I am no expert it solved the problem.I am quite sure the 99 3.4liter is going to need the same work and plan to do it next week.Anyway if you have not yet installed the manifold ,and you have the time and money, you might want to check those headgaskets .In the past I have used toloul to clean those tarry engine deposits.ACE HARDWARE sells it and it works quite well,though I am not sure about it harming the injectors.I would remove them first just in case. http://60degreev6.com/content/34L_GE...Specifications. You will find those torque numbers here. Good Luck.