headgasket

So I picked up a 98 park avenue ultra for 800 bucks after I got in an accident in my regal gs. the park ave was running real rough bad misfiring with a blinking check engine light. Coolant reservoir was just barely low when I checked it. topped it off, there was brown almost plastic looking...

I turned my car on for the first time all day today, it's currently 19 degrees outside and I don't have a garage. Maybe the cold has affected my baby in some way. Anyways, I haven't started it since...I got a ride to the AutoZone to get some dex cool coolant because the coolant in the reservoir...