Excessively foggy windows may be heat issue

Q. My vehicle is a 2006 Chrysler 300 Touring model with a 3.5-liter V-6 engine and almost 85,000 miles. I have an issue in which, more often than not, the windows fog up when I have the heat on low to medium, with vents set to recirculate air.

This doesn’t happen right away, but usually after the fan has been on for awhile. I haven’t been able to determine if fan speed makes a difference or not. This has been going on for several months. I’m curious as to what causes this to happen and how do I stop it.

When the windows start to fog up, I change the air flow dial from recirculate to defrost and the windows quickly clear up. I usually have the air flow dial set to recirculate whether I’m using the heat or A/C.

I normally drive with my window slightly open regardless if the heat or A/C is on or off. Is it a mechanical malfunction causing this, or is it something that I’m doing?

A. My knee-jerk reaction to your fogging issue would be that the heater core may have a leak. It could be a very small leak that does not impact the level of the coolant much but it may translate to a fogging problem.

Typically with this problem, you will have a slight sweet smell of antifreeze and a bit of a film or residue on the inside of the windshield. If it is a larger leak you will notice some dampness on the carpet on the passenger side and you could actually get some steam coming out of the vents.

Another possibility is you may have a plugged condensate drain on the bottom of the evaporator box. This is where the water drips out when you are running the A/C. I would also make sure the cabin air filter is clean and you are getting good air flow through it.

A properly functioning air conditioner is also key to removing humidity from the cabin of your car. The fastest way to clear your windows is putting it in the defrost mode, which should turn automatically turn on the A/C.

Have your system set to recirculate and keep the windows closed as you need to get the humidity out of the air inside the car.

Q. My wife and I both own 2005 year automobiles. One is a Chevy and the other is a Ford. We both have had the same problem of film buildup on the inside of the windshields. Neither of us are smokers. Even when I clean the windshield, it just streaks the film around. I suspect that I can’t be the only person out there with this problem.

A. I am not quite sure how to help you here. Just for grins, I Googled the question “How do I clean the inside of my windshield?” I was surprised by all the sites and forums that came up on this topic, so you are not alone!

Some of the suggestions where to use newspaper and a mixture of water and vinegar, microfiber towels with just water, and many more ideas.

It was also suggested that today’s plastic dashboards have a plasticizer in them and it off-gasses and puts a film on the inside of the windows. It was also noted that using some of the different products to shine the plastics can make the problem worse.

I would suggest doing a little surfing on the Internet and see if you can find a combination that helps with your problem. If you find something that works, let us know.

Ÿ Douglas Automotive is at 417 W. Main St., Barrington, (847) 381-0454, and 123 Virginia Road, Crystal Lake, (815) 356-0440. For information, visit Send questions to

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