I recently put a thermostat in my car. When I went to change it there wasn’t even one in it. So after I got one in I started my car. It ran just fine. The heat was working perfect so I shut it off and picked up all my tools. I then went to starting it again and it wouldn’t start. It would just turn over slowly. So after about 15 minutes it finally started. I drove it for about 20 minutes and it died on me. It keeps doing this after about 15 or 20 minutes after I start it, it will die. And when it dies it takes a few minutes for it to start back almost like there’s not enough juice to turn it over. But like I said if you give it a few minutes it will start right back up.
I am wondering if the temperature gauge is reading hot when it dies. So, I am guessing there was a reason you decided to replace the thermostat in the first place. I am guessing the engine was overheating and you have possibly blown a head gasket. This is common for this engine. I am guessing that the coolant is getting into the cylinders and causing the engine to die. It is also giving a slow crank as the cooling system pressure is built up in the cylinders when you try to restart after it dies. Yet after letting is sit the pressure bleeds off and the engine cranks over a bit faster. A way to be certain would be to perform a compression test on each cylinder.