I have a 1986 Pontiac firebird 2.8l engine. My ex boyfriend accidentally (or intentionally)poured oil into my radiator without my knowledge and I drove the car until it died (no longer starts) after hearing a knocking sound coming from underneath my hood and the car would not accelerate over 20 mph. How can i fix this problem??
Possibly a blown head gasket. Did the car overheat when you started losing the ability too go over 20? If so the engine may have overheated too much and blown a head gasket (why it wont start). Any other details on the no start would be helpful.
Almost certain it's the head gasket. Quick way to confirm is to check your oil filler cap, if it has a milky residue, normally caused by coolant and oil mixing.