how to change a thermostat on a 1999 pontiac grand am 3.4l

Hi aurura2006, Locate the thermostat housing by following the top radiator hose from the radiator to the engine block. You'll find a round casting connected to the intake. Simply remove those bolts and place a new thermostat in the housing, clean off the old gasket material and replace the gasket and sealer. Bolt it back on making sure to tighten the bolts evenly so you don't crack the housing. The trick is getting to the housing because the air intake system is in the way. Loosen the air intake system and pull it back out of the way. There are some small water coolant lines underneath that can be a pain to get off and back on. Good luck!

I HAD GREAT TROUBLE GETTING THE BACK BOLT OUT OF THE COVER FOR THERMOSTAT IS THERE A PARTICULAR TOOL WHICH COULD HELP IN THIS REMOVAL?

Additionally, the two bolts holding the housing are metric and you can find the size online. I can't remember what they were but I ordered two extra bolts in case I dropped one. Sure enough I dropped one but I found it because I had placed a towel across the top of the transmission.

Disconnect your radiator hose from the thermostat housing but leave the 3/8 diameter metal tube attached. This tube goes to the overflow tank. Just remove this tube from the rubber line going to the overflow tank. Remove your air cleaner and air cleaner box all the way to the throttle body. Napa sales are u-shaped tool for $20 that has a 13 mm 12-point box in wrench on one end. You need this tool to slide under the exhaust crossover pipe and blindly get it on the lower bolt. Place a towel across the top of the transmission in case you drop the boat. Take the lower bolt out first all the way then you can reach the top bolt with a 3/8 drive extension and a 13 mm socket. Once you remove the bolt you cannot pull the housing out or move it up or down. The only way to get it out is to slightly rotate it clockwise and it will drop under the thermostat that's protruding. Then you can pull it out. You will have to remove your spark plug wires but just tag them with masking tape. The old thermostat is easy to get out but I suggest applying some silicone to the new thermostat gasket so it will hold in place. Then slide the thermostat housing back at about a 45° angle with the flange and rotate it counterclockwise upward and over the thermostat protruding out. Put your bottom bolt in first and get it started then you can get easy access to the top bolt with your socket and extension. The socket is 13 mm. It was a nightmare and the engineer that designed that needs to start over first grade. Hope this helps.