Bought 2006 Chevy Cobalt 2.2 l about a month and
a half ago. Week & 1/2 ago I was sitting idle for
about 15 minutes and overheated to 219. Was
1gallon low on coolant. Have never seen a leak. 5
days later after not being able to recreate the
situation overheated again at a stoplight 15
minutes. Again about 1 gallon low of coolant still
never seen a leak. On my way to get water pump
and thermostat lost all RPMs stalled out total of
five times. tries to start, randomly wouldn't turn over. Replaced
water pump and thermostat. Won't start at all. Has power and trys but won't. Ran code... crankshaft
positioning sensor. Changed positioning sensor.
Still won't start. Please help. I'm a single mother
and my child hasn't been to school and over a week
because I have no transportation now.

 

Have you checked your oil? If you're losing coolant and not seeing a leak, the only other place it can go is inside your engine. Checking the oil is the quickest way to find that out. If it's milky coffee coloured, there's your problem (and that engine is toast).

 

Yes the oil's fine I went ahead and changed that too since I was already under it. Overheating is not even my concern at this point. I'm hoping that was taken care of by changing the water pump. My biggest worry is why it won't start now. I cleaned out the throttle body earlier and it actually cranked for about 2 seconds and then died did that three times. I did also notice that after I stopped turning the key over and trying to start it for at least 2-3 seconds it kept going and trying to start itself. Like it wasn't technology that I had turned the key backwards I even tried to pull in the key out and it still did it. Not sure if the two are related

 

If it does actually turn over but dies, it's also possible that your MAF is dirty (I had this issue myself, ended up thoroughly cleaning my entire airtake system). The only other thing I can think of is that you might have had air bubbles in the system and when you added coolant into the system you filled that up. Also, the thermostat could be bad.

If you can, unplug the MAF to your airbox, which I'm assuming is stock, and when you turn it on, see if it idles by itself; it should, but may do so poorly. Otherwise if it just dies, you may have to step on the gas pedal just as you're turning it on and you'll need to hold it so it until it does idle by itself. When I did this, I had to flex the pedal for more/less gas to keep it around 2000 RPM as that was the stable point. I believe after 10 minutes it finally settled to a regular idle - and this was after cleaning everything.

 

The key issue is a faulty GM thing and it was recalled.

 

I don't think it's MAF related (but wouldn't rule it out). The car cranks and starts with VE, then switches to the MAF after the fires. I just went through this with my car (dead MAF).

It's entirely possible that by trying to clean the throttle body, you killed the throttle body - the car tends to throw correlation codes when that happens though. I'm not sure how finicky the 2.2L and 2.4L throttle bodies are, but that's a common problem with the early 2.0L's.

Also, 219°F in this car is not overheating; I think the stock fan units are setup to kick on to 100% around 225°F. The disappearing coolant is an issue, though. Probably worth pulling the spark plugs to look at them - maybe just replace them if it's been a while (they're likely not your issue though). If your head gasket is busted and your coolant is leaking into a cylinder, that could be your issue. Although, that's typically accompanied by white smoke out of the exhaust.

Start simple. Check fuses. Does the fuel pump prime when you turn the key to on? You may have to be outside of the car to hear it.

 

Thanks, I think I figured out the issue with it not starting. I was checking the fuel pump relay. I tapped in a few times and it started on the next try. I've only drove it once, the temp is still going up to 198. Which makes me nervous cause it always ran a steady 185. The 2 times it got to 210-219 it was steaming from the water reservoir. So I'm hoping you guys are right and it's nothing to worry about. Thank you guys so much!

 

Well, it shouldn't be steaming from the reservoir when it's at 210-219, either. What antifreeze to water ratio are you using? And are you still using the OEM pressure cap on the reservoir?

You're in south Texas, so you can safely run a two-thirds water to antifreeze mix - that's what I run and I'm in DFW. Water cools better than antifreeze. I use a 1000 mL measuring cup - two cups water to one cup antifreeze. Also, you should be using demineralized or deionized water - not tap water.

And if your reservoir cap isn't applying the pressure required to the system, then that might be part of your problem. The cooling system requires pressure. Water boils at 212°F without the cap pressure, and I think a 50/50 mix will boil around 220-225°F. With 15 psi of cap pressure, the pure water boiling point jumps to 257°F (this is part of why you don't remove the "radiator cap" when the system is hot - removing the pressure can flash boil the system, causing an eruption of coolant).