RadiatorDear Ole Mechanic;

This morning was a cold one and since my heater was not putting out much in the way of heat, I noticed that my temperature gauge wasn’t getting up to normal temperature.  I got half way to work before the inside of my car got somewhat warm.  It put out good heat last winter.  What's wrong

Cold Ride

ThermostatDear Cold Ride;

You didn’t give me much information about what kind or what year your car is, but I will still try.  I suspect that the engine coolant thermostat is either opening too soon or more than likely it is stuck open.  In other words, your thermostat has gone bad and it needs to be replaced.  The thermostat is what is used to get the engine up to operating temperature quickly.  The engine is designed to operate at around 190 to 205 degrees Fahrenheit, depending upon the year and make of the car.  Any cooler than that and the oil does not get warm enough to properly lubricate the enginem and it will wear out sooner.  Also, the emission-components don’t really work right to clean up what is going out the tailpipe.  When the engine runs too cool, the computer for the electronic fuel-injection will put more fuel into a colder engine so that it will run right.  It acts like a choke in an older car, so that it doesn’t cough and sputter when cold.  That will cause poor fuel mileage, and extra fuel can dilute the engine-oil and cause even more engine wear.  Fortunately, the thermostat didn’t stick closed, because that would have caused overheating and would be even more of a problem.

AntifreezeWhile you are having the thermostat replaced, it would be a good idea to have the cooling system flushed and the antifreeze-solution replaced.  You didn’t say what year your car was, but almost all auto manufacturers call for flushing and replacing the antifreeze every two to five years.  That is because antifreeze can break down and can cause corrosion problems in the radiator and/or engine coolant passageways and/or plug up the heater core.  That would mean no heat or defroster heat inside the car. 

The flushing and replacing the antifreeze is considered a maintenance item, like changing the oil, so don't expect any warranty to cover the cost.

One note of caution!  Do not open the radiator cap until the engine has completely cooled down.  Even a low temperature-gauge reading can still be 150 degrees and the coolant will come out under pressure and can scald or burn you badly.  Whatever you do, DO NOT use 100 percent antifreeze, as it does not transfer heat very well, and it needs to be mixed 50/50 with water.  This is a job best left to your favorite mechanic or repair facility.

Herr Professor Nuzanbolts