Here’s why the windshield is fogging up

Ask the Auto Doctor

DEAR DOCTOR: My father owns a 2009 Lincoln MKS with 48,000 miles. After 1.5 hours of driving with the outside temperature of 66 degrees with no a/c or heat on, I noticed fogging on the windshield (not heavy). It also happens in winter when the heat is turned on. Could this be a small problem now or a big problem down the road?

— Ursula

DEAR URSULA: Today’s vehicles are nearly air tight. Without air circulation — and under the right humidity conditions — windows will fog up. The HVAC system removes the humidity from the interior and draws in outside air in most cases. The air conditioning part of the system actually removes the humidity. Always make sure the carpet is dry, and remove the floor mats occasionally to let the carpet breathe. In most vehicles with automatic temperature control, the A/C compressor will come on anytime the ventilation system is on. In vehicles with a manual A/C, the compressor comes on when the system is set to defrost.

DEAR DOCTOR: I own a 2003 Buick LeSabre and have been alerted to “service stability system.” I have been told that one of the rear shocks is leaking and that I should replace both rear shocks with a kit specifically made to replace the OEM system. I do see what could be the evidence of a leak in the driver side shock, but the compressor runs for less than 5 seconds at start-up and does not run again. The service stability system alert comes on at odd moments, at times long after I start out and at times soon after. What are your thoughts?

— Jim

DEAR JIM: Rear air shock replacement kits are a lot less expensive than the General Motors factory Delco brand, though the stability system alert may not be connected to the leaking air shock. The technician should read the codes and follow the trouble flow chart found on Alldata or Identifix. Whatever the problem, as long as the suspension and front end have no worn parts, the car should be safe to drive.

DEAR DOCTOR: I have a 2005 Nissan Altima 2.5 with 61,000 miles on it. The car has never had a tune-up. I replaced one ignition coil and I change the synthetic oil once per year at inspection time. At this point should I try to change the spark plugs or leave well enough alone? I’m afraid of breaking the spark plugs in place.

–Bob

DEAR BOB: This 2.5-liter four-cylinder engine should not have any problems with changing the plugs. I would certainly try to remove the spark plugs without using a lot of force, and make sure to use some dielectric grease on the coil boot and spark end where the coil goes on.

DEAR DOCTOR: I’m the original owner of a 1977 Toyota Celica. After five years as a daily driver I decided to keep it as an eventual classic car. Because I drive so few miles, the plugs probably haven’t been changed since the early 1990s. How would you suggest I proceed? It runs fine, so I’m wondering whether I should change them.

— John

DEAR JOHN: I suggest replacing the spark plugs and make sure to use the factory plugs, or factory equivalent. Spark plugs on these older Toyota vehicles do not typically become frozen in the cylinder head. I also recommend taking a look at the transmission fluid and all other fluids, and check the tire date code and treads for cracking.

DEAR DOCTOR: I use Mobil 1 synthetic oil in my vehicles. Is there a difference between Mobil 1 Advanced full-synthetic oil and Extended Performance 15,000 Mile Advanced full-synthetic oil? My Toyota RAV4 takes 6 quarts of oil, and sometimes when I purchase the oil the store only has 5 quarts in stock. Can I use 5 quarts of advance oil, and 1 quart of extended oil?

— Joe

DEAR JOE: All oil companies have their own secret formula for oil. The difference on these oils is the additive package mixed in with the blend. I would suggest that — whatever brand oil you use — to make sure the oil specifications are identical to what is recommended by Toyota for your RAV4.

Damato is an ASE-certified Master Technician.

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