Q: Overheating and hissing

You stated your coolant was about halfway. It’s an important detail to know where you are checking your coolant level. Are you checking in the coolant overflow jug, or in the radiator after you remove the radiator cap. Also, you should be checking it while it’s cold or at least cool. Checking it hot is dangerous and not very accurate.

If the coolant level in your overflow jug isn’t necessarily an accurate indication of the rest of your cooling system. If the coolant level in the radiator is half full, then you have a coolant leak and have been lucky you haven’t experienced overheating until now. Either way, your vehicle is overheating and will need to be repaired.

If the cooling system is low, then you will need to locate the leak and fix it. I would also recommend replacing the thermostat as well. Thermostats are usually damaged when a car overheats. So replacing it maybe necessary. It’s at least a good idea.

If the cooling system is full and the car is overheating, you will likely need a thermostat or possibly the water pump impeller has failed. Either way, I would begin by making sure the cooling system is full when cold and checking to make sure the thermostat is opening as it should. This can be done by running the motor from cold, touching the radiator hose that the thermostat feeds, and wait for the hose to become hot. When it becomes hot, the thermostat has opened. The most accurate way to monitor this is with an infrared thermometer. This way you can monitor the actual engine temperature while the car is warming up. If it reaches more than about 220 degrees Fahrenheit, and the stat hasn’t opened, (the radiator hose hasn’t become hot), then you likely have a thermostat problem.

If your water pump impeller has problems, this is usually a result of a rusty cooling system. But water pump impellers have been known to fail in other ways. Either way, you need to test for coolant flow. This is done by removing the water pump bypass hose, coolant bleeder hose or a heater hose and starting the car. Be careful if you are doing this hot. You should see coolant come out of the removed hose. Of course, be prepared for a mess and some way to catch the coolant or clean it up after. Don’t expect the kind of pressure you get out of a water hose from your house, unless you rev the motor. If there is little to no flow, I would suspect the water pump. But keep in mind, choosing the correct hose to test for flow takes and understanding of the dynamics of a cooling system. They are different for every vehicle.

There is also the possibility of failed head gasket. But these motors are not known for that, so I wouldn’t expect it, unless you have driven it to far with a low coolant level. If you have, every vehicle is prone to such a failure.

I’d recommend having your car looked at by a certified technician, they will be able to diagnose your overheating symptoms firsthand and make the necessary fixes to get your car running normally again.

Good luck. I hope I have helped you.