Oldsmobile/Buick Repair: 96 Buick Skylark GranSport engine/Cooling, buick skylark, coolant temp

Question
Hey Pete you seem to know your stuff so if you could help me out I would appreciate it. Earlier this spring I had forgotten to replace the fuel cap and the check engine light came on.  After replacing the cap the light went off until tank went below 1/2.  After a couple top offs it stayed on. Code reader says  #5 missfire and coolant temp sensor.  Replaced the sensor and the plugs and wires.  Light still on and still #5 misfire.  Since this I have had to change the alternator the 2nd on this vehicle.

Since last summer i have had to continually add coolant (gallon at a time).  Since the engine light first came on, I've replaced the water pump and didn't have to add anymore for a few months.  Now the car doesn't hold coolant, boiled over the resevoir once.  The other day I drove about 30 sec to the store and when I got out a few minutes later it wouldn't turn over.  Jiggled the wires and pumped the gas and it finally started but wanted to stall at stops.  Any suggestions before a ditch it.  It has 150K hwy miles so I don't want to have to put a lot more money in to it.  Again thanks for any help you can offer.

Answer
Hello Adam
this sounds like a bad head gasket it is triping the senser and u might get to reset for a day or to but i have sean it before it is time as you say to ditch it it is a nice car thoe but it will be a money factory to put up with hope i have explained this good to u pete