Replaced my stuck open thermostat!


Original poster
Dec 4, 2011
Well, I got a P0128 about a month ago so I picked up a new thermostat and coolant.

First, I would like to say thank you to GMT Nation and all the people on here for all the great info on the subject. I'm pretty sure that I read all the posts on P0128 and thermostats to gather as much knowledge as I could, so I knew what I was getting myself into.

Second, Wow what a PITA this was to replace. For is being the first time ever really working on the engine of my Trailblazer, it was a learning experience. Taking out the alternator was probably the hardest thing of the whole job. I did it the Chilton way, by removing the alternator from the vehicle. Talk about a tight fit. I had to cut off the little tab on the battery box that holds the battery cover on. I removed the battery cover a week after I bought the Trailblazer (6 years ago) and threw it in the trash. I needed the room for my amp wires.

The whole job took me about four hours (with lots of breaks). If I wasn't fat and lazy, and I didn't have to run to Napa to get a new hose clamp (broke old one), I could have done it in 2 hours.

In a whole it wasn't too bad of a job to do. The only thing that took the longest was removing the bottom bolt on the alternator. I sawed one of my coworkers wrenches in half (he said I could) to make it a stubby. That made the job a lot faster and less hitting of the fan blades.

Here are some pictures of the thermostats side to side. As you can see the old one (Left) is stuck in the open position.



Boricua SS

Nov 20, 2011
gotta love gettin in there and getting your hands dirty... bet you learned alot more by doing the job yourself, then relying on someone or a mechanic to do it for you... :thumbsup: glad it all worked out for you...

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