99 GM coolent leaking!!

Hello, I have a 99 and I found out where coolent was leaking from it was at the thermostat housing. So I bought a new thermostat and gasket but the gasket is just a O-ring so I took off the housing replaced the thermostat and put the o-ring in the same place the old one was which drops down on top off the thermostat. I then cleaned up the corrosion on the housing and put it back on and tightened. Started the vehicle back up and it was leaking AGAIN from the housing so I took the housing back off and cleaned. Then I put instant gasket around the housing and its still leaking!!! PLEASE HELP!!!

You probably have a cracked intake. Remove the housing again, dry it as good as you can and spray carburetor cleaner on the outside of intake. As the cleaner dries, if there are any cracks in the plastic, it will show up as wet lines longer than the smooth places.

Common problem that wound up being settled by a class action law suit.

http://www.fordmanifoldsettlement.com/

The cracked manifold is a VERY common problem and sounds like you have it. The lawsuit settlement was for cars 7 years old or less. I doubt your car is covered by the lawsuit settlement.

There are some very good DIY instructions here...

http://www.autoclinix.com/Manifold.htm

if you care to tackle the job yourself. I've done it twice (2 different cars) and it's not too bad.