Hello,
About 2 miles away from home, car felt like it was running rough, thought it was in my head until I parked my car and turned it off and it felt terrible. I popped the hood open and coolant was boiling and there were a few drops of coolant spilled under tank. Checked coolant temp and it was at 230. My car usually runs around 200. (AC was on while driving around). Waited about 30 min and started car, still felt rough and low coolant message. Any help/suggestions appreciated! Thanks.

 

Add coolant? How's the fan, i've seen them crack blades and cause pretty severe vibrations on the 2.2/2.4L single fan setup. What year/model of Cobalt?

Any CEL?

Take it to a shop?

 

Coolant and fan are good. It's a 2008 LNF. Heats not working so I'll give the thermostat a try and go from there

 

Porous block?

 

Mine started with the same problem brought it in and like stated above block was cracked 6000 in repairs cars been on the shop over a month now.