2001 blinking check engine light...

[miklin]

Check engine light comes on...3 days later overheats, check engine light flashes. Removed thermostat, put coolant in. Engine light flashes spits & stutters like it wants to stall, temp guage gets hot then cold. Had diagnostic test at Advance Auto and codes were P0156 (02 sensor circut malfunction-bank 2 sensor 2), P0301 (cylinder 1 misfire), P0302 (cylinder misfire). Is my head gasket toast.... and how much to fix myself or garage?

[shorod]

I doubt the head gasket it toast, unless you are losing coolant and smelling it in the exhaust.

The flashing CEL is probably due to the P0156 code as that is an emissions-related code. You should figure out the reason for the misfire codes as that will likely fix the spitting and sputtering, and possibly remedy the O2 sensor code. The misfire could be plug wires, spark plugs, the coil, or possibly a vacuum leak.

-Rod

[miklin]

We can smell coolant and some kind of liquid is leaking out or around the exhaust.

[shorod]

It is not unusual in the colder months to notice condensation (water) coming from the exhaust. If the liquid you notice doesn't have an obvious odor or color, it's probably just the condensation. Water is a byproduct of the catalytic conversion, converting unburned hydrocarbons to water vapor.

Do you smell coolant in the cabin, under the hood, near the exhaust, or just in general when near the car?

-Rod

[miklin]

I'm not sure about the smell inside the car, but you can smell coolant outside near the car.

[shorod]

You have a few options to determine what the problem is, but you're going to have to be willing to get a bit dirty for pretty much any of them. You need to determine the source of the coolant smell. Since you also have misfire codes, a good place to start would be by pulling the spark plugs for cylinders 1 and 2. Unfortunately these are both on the bank nearest the firewall. However, if you pull the plugs and one or both have a greenish tint or smell like coolant, then you are probably looking at a head or head gasket issue. If they smell like fuel but don't show signs of trying to burn coolant, then you probably don't have a head gasket issue.

If you can find a cooling system pressure tester or dye kit to borrow, you could go either of those routes to determine if the cooling system has a leak and likely where the source of the leak is. Unfortunately just saying you can smell coolant outside the car doesn't help us much in giving suggestions on the issue.

-Rod