Input is - you had spark plugs with over 100,000 miles on them, even a Ford part would be an improvement, but engine was designed for the aforementioned iridiums.

 

Besides the fact that Delco designed the entire ignition and electrical system the iridium plugs last at least 100,000 miles and many have gone for the life of the car.

There is something sick about putting Ford plugs in a Chevy. Maybe try putting Lucas coils on it?

 

Other brands of sparkplugs have caused problems in the past and that's not gonna change. Use the specified AC Delco.

 

It's like we've never tried other brands and learned a lesson, plugs, coolant, thermostats, the list is long!
In actuality we personally don't care what you use, just friendly advice as to what works in the HHR.

 

My original plugs came out when I changed them at around 175K miles! And even then they were functioning fine I just did it for peace of mind!

 

OP:
Check your your oil in the morning, or after long cold soak. Look for orange dexcool...

My oil cooler went, and it's more common than a head gasket on Ecotecs. What happens is the coolant remains at a higher pressure longer than the oil at the cooler, and it pushes through. The cooler is cheap and easy, IF you catch it. I didn't, and blew my engine.

I read about this, and found orange on the morning I tossed a rod.

 

A 2011 wouldn't have that style oil cooler like on the SS and 2006 and some early 2.4's