Does 2008 HHR come with a failsafe thermostat? One of my radiator hoses blew and I replaced it along with a new radiator and it won't start now. The engine keeps turning over but it won't fully start. Any ideas?

 

What do you think a thermostat would have to do with starting? It is just a standard mechanical t-stat.

How badly did it overheat? Probably internal damage.
Take the cam cover off and see if the timing chain is there or loose.

 

Yeah it overheated bad I think. I was driving on the freeway and I didn't notice anything until there was a cloud of white smoke behind me. And then the engine died and pulled off to the shoulder. I didn't notice the temp guage at all by the time I did, it was at zero along with the rpms. Car scanner is throwing p0326, p0336 and p0117. I will pull the cover and check it out.

 

Yeah engine was at 300°

 

300 degrees F ? If so, it's dead.

 

Knock sensor, noticed a knock

https://www.obd-codes.com/p0326

Crank shaft position sensor, noticed the timing went south,

https://www.obd-codes.com/p0336

Engine temperature sensor, noticed the engine was overheating.

https://www.obd-codes.com/p0117

Those sensors are fine, they did their jobs and sent signals to the ECM and BCM, but I’m thinking the overheating and coolant steaming, cause the head gasket to fail, and the pistons stopped and ceased, and the engine is done!
Coolant in the oil, will wash out the oil in the crankshaft bearings and stop the engine from turning over.

 

Here are some photos. The burnt spark plug is from the second cylinder.

 

 

Blown head gasket or hole in the piston. Either way, with it having run that hot, that engine is gone.
Time for a replacement engine or sell the car as is.

FWIW. Doesn't matter now but those appear to be the incorrect plugs for the HHR engine.

 

Good eye FMG , wrong plugs, and that’s not burnt it’s oil soaked, pretty sure it new or used engine time! That one is toast.
if you decide used engine, send hellshotrod a PM , perhaps David has a good used engine.