About every 36000 miles or so. Even thou you have DexCool, which is recommended every 100k miles, don't do it. DexCool is death for a engine. Wish GM would just get rid of it, and go back to the good old reliable antifreeze.
You have reinstall the head gasket. It has been not tighten enough or damaged. Anyway the replacement was not done properly.
Your engine can lock up if there's no water in the system.
If your engine has been damaged it may be worthwhile to purchase a remanufactured engine. A 1986 Buick Riviera currently has 102,000 on a remanufactured engine(ReCon).
The 944 cooling system is a closed system. There is no radiator cap. Coolant should be added to the cloudy plastic overflow tank in the engine bay on the drivers side. With the car cool, add coolant until the tank is full. Start the engine, and continue adding coolant until maintains the level at the full line. When the system is full, close the cap. There is a bleeder screw (8mm head?) on the coolant outlet on the front of the head of the engine. It is near the distributor, at the highest point of the engine. Loosen the screw (it is actually a banjo bolt) a few turns to let out as much air as possible. Tighten it when only coolant comes out. You are done!
engine smoking indicates overheatingdue to low coolant and/or oil if it shutdown because of overheating you may have already done serious damage
The term "boiling", I am assuming, is referring to the coolant bubbling out of the radiator or overflow. This indicates that your engine is overheating, and should be shut off IMMEDIATELY. It is possible that er-repairable damage has already been done to an engine that has boiled over.
If it is a V6, the cam belt, water pump, spark plugs, coolant, and thermostat, should have been replaced at 110,000 miles. If you have not done so, know that this is an interference engine. If the belt breaks you will have engine damage. If it is a 4 cylinder the spark plugs, coolant, & thermostat need to be replaced. Have brakes and suspension inspected.
Probably because you have a blown head gasket. Get a compression check done to be sure.
The longer you wait the more damage will be done to the engine due to the coolant mixing with the oil.
You can keep driving the vehicle if you want to destroy the engine. The more you run the engine the more damage will be done. Coolant mixing with the oil will cause severe engine wear.
a testicular exam should be done once a month
I heard that you should have ducts cleaned but I don't know how often. How often should furnace duct cleaning be done and how much does it cost?