Precision driving : Auto ailments are often obscure

The breakdown of our precious rides can be either commonly straightforward or somewhat out of the ordinary. A flat tire shows off quite prominently as no longer round. A hole in a hose will evidence its presence via a geyser of anti-freeze. A faulty oxygen sensor will even set off a warning light. Certain motorized maladies, however, are less common, and harder to spot.

Two failures of the more subtle variety are leaky heater cores and faulty thermostats. These potential problems have symptoms that are likely to show up in the winter.

Although I haven’t come up with a better solution, I think that the way our cars are heated is archaic. Basically, we are warmed within our cars and trucks by air that is fan forced across a small radiator. That’s right, a smaller version of the radiator under your hood is mounted under your dashboard. Just like its larger counterpart, the small one, called a heater core, is full of anti-freeze/water mixture (coolant). This mixture is continuously routed in and out of your passenger compartment through hoses connecting the heater core to the main cooling system. Not a bad system when intact, but one that may fail after a few years have passed and a bunch of miles are accumulated.

We all know that radiators occasionally spring leaks, and unfortunately, the “mini-radiator,” or heater core may also. This is why I think that there has to be a better way to heat an interior. How about an electric element, auto engineers? Both Volkswagen and Corvair automobiles experimented with gas-fired heaters in the 1960s. Guess what? Fire and/or explosions could and did occur. Occupants have even been burned with hot engine coolant mixture during sudden failures of common heater cores.

There are usually signs of heater core leakage before a major blowout manifests itself.

It pays to monitor your coolant level under the hood for many reasons. The coolant mixture is not consumed during normal operation, so any loss is a harbinger of component failure. Often, coolant leaks start slowly, warning of a needed repair before you are stranded. Coolant loss may occur through hoses, radiator, water pump, head gaskets, soft plugs, or your heater core.

When the anti-freeze/water mix begins to seep out of your heater core, you may see a drip of liquid at the lower seam of you heater box. In the early stages of leakage, the most common symptom is abnormally steamy windows. As the heater fan blows air across the leaky core, it sends the moisture into the heating and defrosting ducts. If activating your defrost mode makes your windshield or window even foggier, you probably have heater core seepage. When this occurs, you may also smell, or even taste the “sweetness” of anti-freeze. Fogging formed from a leaky core is also difficult to wipe off of the glass — almost greasy.

Due to the labor required to remove them, heater core replacement can cost $400-$1,000, so you will want to be sure of the diagnosis before repairs are made. One thing for certain — if you have fogging and coolant odor now, you will soon have a puddle on your floorboard.

Thermostats are simply valves that either stop or allow coolant flow between your engine block and radiator. They can stick closed or open, or lose their calibration.

When a thermostat sticks closed, it’s quite obvious, as the engine will quickly overheat. In this case, the coolant in the engine block gets hotter and hotter, with no allowed exchange of cooler coolant from the radiator. Also if an engine overheats for any other reason, it can alter the calibration of the thermostat. Watch your temperature gauge to monitor this condition. When fully warm, most engines are designed to run at 195-210 degrees.

The most common thermostat failure is sticking in the open or partially open position, and typically becomes a problem in winter. The failure may happen in the summer, but with high ambient temperatures, your vehicle may run in the normal heat range even with a wide-open stat.

When outside temperatures drop, however, the thermostat needs to cycle open and closed to maintain proper engine heat. This is particularly important nowadays, as computer controlled engine management is upset when a vehicle never reaches full operating temperature.

As the days get colder, watch your temperature gauge to see that your vehicle gets up to temp (around 200 degrees) in 10-12 minutes of operation. If it takes half a day of driving to get that high, of if it never does, it’s likely time for replacement of your thermostat. For cars with no temp gauge, lukewarm instead of hot air at the heater outlets may also be a sign of a faulty stat — or even a clogged heater core (another story).