2006 Cobalt losing coolant and running rough

Hi we have a 2006 Chevy Cobalt. The engine is a 2.2 according to oil change records (hubby is gone and I know nothing about cars). It has around 56,000 miles on it. All of a sudden several things have went wrong with it. I don't know if they are all related or not since I know nothing about cars, but since they started happening around the same time I assumed they were. To start with we started losing coolant. My hubby keeps filling it up. There is no coolant in the oil and none visible on the ground. Then it started running really rough when starting up. The sound it is making sort of reminds me of when we had to change the oxygen sensors in our old van. Then just the other day we started hearing a noise under the passenger side. It sounds like water sloshing around in a tank whenever he has accelerated and then suddenly stops. The check engine light came on around the beginning of all this and whenever we had the mechanic hook it up it said it was a knock sensor. He changed that and a week later it still hasn't done any good. Our check engine light is no longer on, but it still sounds rough, is losing coolant, and the sloshing water sound is still there. If anyone could give me some helpful advice or suggestions it would be much appreciated. Thanks!

From what you have said, there is a good possibility that the head gasket is blown slowly allowing coolant into one or more cylinders which makes it start hard once coolant has been able to pool up. Low coolant could make the noise you are hearing as it flows through the heater core if it is low enough for there to be air in the heater core. If you want to check it out yourself, you will need a ratchet, 10mm socket, 6-12" extension, 9/16" spark plug socket, compression tester, and cooling system pressure tester(with an adapter for your coolant reservoir). Remove the electrical connector from the cover over the top of the engine, remove the 4 10mm bolts from the cover, remove 4 spark plugs, remove the fuse for the fuel pump. Thread the compression tester into a cylinder. Have someone crank the engine for 4 full revolutions, or until the pressure on the gauge stops climbing. Repeat on the other 3 cylinders. Compare the readings, they should be within 10% of each other. If one is significantly lower, then most likely the head gasket is blown on that cylinder. With the spark plugs still out, install the cooling system pressure tester on the coolant reservoir and pressurize the system to what the pressure cap says on it. I believe 15 PSI. Watch the pressure, if it drops off, you have a leak somewhere. From the combination of symptoms you described, the head gasket is the most likely, but pressure testing will make drops show up on the ground where they might evaporate with the engine running and hot. Let it sit for as long as it takes for the pressure to drop. If the engine was hot when you began, you will lose roughly 1 PSI for every 10 degrees Fahrenheit it cools, so keep the pressure at whatever it started at if the engine is cooling. If you let it sit and dont see drops on the ground, look in through the spark plug holes and see if you can see any coolant. It may be hard to see in without a boreoscope (expensive tool, don't go buy one just for this). You could cut a long strip off a white towel and drop it down into each cylinder and see if one turns it orange. Just be sure you hold on to one end of it, you don't want it stuck in there.

Wow.. I believe I've heard of maybe one report of coolant leakage from the water pump cartridge into the timing chain cavity due to a blown seal, but you'd notice that right away by checking the oil I'd think. Hopefully it's not getting past the in-tank ATF cooler and into the trans?!? Trans would act all funky should be your indicator there.

Joel