Fluctuating Engine temp Guage and Coolant Leak

I have a 2003 Grand Prix SE, 3.1 V6. One day the heater started blowing cold air as the temp guage rose to 190-200 ranges, the guage then dropped and blew warm air. The guage kept going up and down every time I drove it. 2 weeks later it just stopped blowing warm air at all. Took it too get serviced. Mechanic claimed it was needing the water pump replaced. He replaced it, and the heater worked great. A week later I noticed coolant leaking slowly. Took it back and they ran a pressure test, and it held pressure for over 20 mins. I took the mechanics word for it since the heater was still working. Its been one month and the heater has still been working good untill today, when it behaved in the same manner as before, albiet to a lesser degree of severity. Leaking persists as before, and now their is very little left in the resevoir after the engine is cold.

Any ideas? Is this two differant issues? I'm think an intake manifold leak, and then an air bubble in the cooling system for the rising and fall of the temp guage with the warm/cold air fluctuations?

And its leaking where?

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Methinks, it wasn't the w/p......did he definitely show you that the weep hole was leaking?

He probably refilled the system and did a good job of venting the system of air, so that the heater was ok......now the same leak has created an air pocket again and is starting to cause the same problem....

You have a leak....need to check all the usual places....if you see nothing externally, than it could be a lower intake.......

He did not show me anything. He ran a pressure test the second time after I brought it back with the leak and he claims it held pressure.

I checked for exact location. I cannot find it with my eye, just a general area it seems to be forming on the bottom of car. Left front, in front of the axle, directly below the serpentine belt system.

Funny thing is today after driving it, it has become an extremely minor leak just one drop formed and never fell to the ground, and my resevoir was the same spot it was last night. This comes after last weekend when I witnessed it dropping out fast and pooling under the vehicle.

Temp guage still fluctuates as I drive it, didnt have heat on today, it was hot outside.

Thanks for all replies thus far...

If the water gets low it will bypass the heater core. This is why you are losing heat. As stated air pockets will cause fluctuations in temperature as well. You need to locate the leak and find out what needs replaced.

The saga continues. Took the car to differant repair shop. They did pressure test, and it held pressure again. They degreased engine and visibly checked for leaks again. Nothing found. They then bled the system for 45 minutes and replaced all fluid. Test drove it, heater worked fine, and after the drive there were no leaks noted.

I pick it up drove it 2 miles home, and, I could not beleive it, there was coolant pouring out from the same spot all over my parking space.

Am I getting screwed around here by these differant repair shops? No one can locate this leak.

Thanks....

If you see coolant on the ground, there is either a leak or it is boiling over.....if you can't find it, then have a dye added to the coolant and find the leak with a black light....

The saga continues. Took the car to differant repair shop. They did pressure test, and it held pressure again. They degreased engine and visibly checked for leaks again. Nothing found. They then bled the system for 45 minutes and replaced all fluid. Test drove it, heater worked fine, and after the drive there were no leaks noted.

I pick it up drove it 2 miles home, and, I could not beleive it, there was coolant pouring out from the same spot all over my parking space.

Am I getting screwed around here by these differant repair shops? No one can locate this leak.

Thanks....
I doubt you're getting screwed. They just did not see the problem when they had the car. If you can see coolant coming out, your problem is much easier to solve. All you need to do now is pop open the hood and get under it and see where it's coming from. You can at least determine which side, or what section of the engine compartment it is dripping from.