Foggy windshield could indicate leaking heater core
Mywindshield is fogging up when I use the defroster, much worse than before I turn it on. Why is this? I’ve been carrying a towel with me and not using the defroster. — Carol P.
It sounds like your heater core may be leaking. This is a cigar box-sized liquid/air heat exchanger that is typically located within the heating/ ventilation/air conditioning (HVAC) housing behind the instrument panel, or sometimes within a housing accessed from the engine side of the firewall. Engine coolant is circulated through the heater core and your HVAC system blows air through it to give you warm air for cabin heating and defrosting. Should a heater core begin to leak coolant, one will typically find sticky wetness on the passenger side floor and a foggy windshield, as you have noted. The 50/50 coolantwater mix is a somewhat slimy fluid, perhaps green, orange or red, often with a sweet odor. If you should find wetness in the carpet beneath the instrument panel, it’s best to act on this fairly quickly because the coolant leakage can be messy to clean up as it saturates the carpet and insulation beneath it. Also, your cooling system fluid loss could lead to engine overheating!
You didn’t mention your car’s make or model. On some vehicles heater core replacement is perhaps a two-hour job, while on others it seems they built the car around the part, requiring many hours, a jackhammer and foul words to access it! A heater core typically costs between $50 and $150 for the part, plus installation, new coolant and perhaps a hose or related components.
Proper cooling system service is important to help ensure long life of the heater core, radiator and other engine parts that are in contact with the coolant. It’s also a good idea to be certain that engine related electrical components and any added accessories are properly grounded. Electrolysis can accelerate corrosion in the aluminum heater core as well as the radiator and other expensive metal parts. I hadmy Fusion repaired for a “check engine” light and paid $470 to have it fixed. Nowthe light is back on again. I’m getting a song and dance from the guy saying it’s something else wrong nowand not their responsibility. Howcan this be? — Tim L.
Yikes! Did the repair shop document the diagnostic trouble code that occurred in conjunction with the first incident? If the sameDTCis occurring now, and it’s been only a short time (90 days or 4,000 miles is the duration of responsibility inmy state) it’s possible they didn’t get it fixed right the first time. It’s also important for the diagnosed fault (and whether it’s continuous or intermittent) to be documented, along with the repair performed andmethod employed to validate repair success (typically running the appropriateOBD-2 monitor with noDTCreoccurring).
There can be perhaps a hundred or more possible reasons for the check engine light (MIL— malfunction indicator lamp) to illuminate, as the on-board diagnostic system is capable of determining a large number of faults. One day there could be a P0440 code (and illuminated light) due to an improperly tightened gas cap, and perhaps a week or two later another code, P0171 and light, due to a dirtyMAFsensor sensing element. In this case the repair shop could not anticipate or be responsible for the second check engine light incident.