Just got my MINI to its new home in Louisiana, and everytime I drive after dark the windshield fogs up on the outside. Bad enough I have to leave the wipers on so that I can see at all.

I have the AC on my feet and the fan on very low.

Is there some thing to treat the windshield or do I just have to live with it in the humidity?

Smiley

 

Wish I could help. Have never had that problem. I know its humid down there, but that is a little ridiculous. Maybe someone else that lives in a high humidity area can shed some light on your problem. Best of luck to you!

 

That's going to happen any time warm, moist air hits a colder surface. In the warm air, the water in the air is in the form of vapor, so you can't see it, but when the air hits your windshield and cools down, it can no longer hold the water in vapor form, and the water condenses out as a liquid, forming the fog on your windshield.

If you can find a weather report online for your area that gives the "dew point", that will help explain things. The dew point is the lowest temperature that will keep the airborne water in vapor form. Once the air temperature drops below the dew point, you get fog.

Basically, any time the dew point and the ambient temperature are within a few degrees of each other, you're more likely to get fogging on your windshield, since the windshield doesn't have to be very much colder than the outside air for the air hitting the windshield to drop below the dew point.

As an example, the temperature in coastal Louisiana right now is in the mid-70's, and the dew point is in the low 70's, meaning there's not much of a split between the air temperature and the dew point. So, if you were to go drive around New Orleans right now with your A/C on (even on low), you'd likely get fogging on your windshield.

Likewise, the temperature here in Salinas, CA is 60F, and the dew point is 56F, so the forecast is for low clouds and fog tonight.

 

that's one thing I don't miss since I moved from Florida to California.

 

Yep, I lived in NO for a year and hated that. I treated my window with RainX antifog and it worked OK but not a solid solution. You might give ti a try.

 

Live about 60 miles south of Fort Polk in Lake Charles. All I can say is welcome to the South. Just remember when you run your AC alway use the recirulation setting or you will have a musty smell caused by creating an enviroment that mold loves. We will have to get together and I will show you around your new home state.

Stan Francis

 

Man that was brilliantly explained. Its been many times I worked at getting that in my head when I was working on my private pilots license, and never did it make that much sense to me. Thanks!

 

Thanks - I had a good meteorology instructor in flight school, and I think most people can understand things better when given a brief explanation of the math/physics behind why they work the way they do.

Some of the other officers at flight school were only given the guideline "When the outside air temperature is near the dew point, look for fog", but they didn't really know *why*, so not only couldn't they fully understand it themselves, they didn't have the ability to teach it to anyone else, except to repeat the standard guidance.

 

Scott, where do you fly? My father-in-law flys out of South County in San Martin all the time. He got his license 2 years ago and he's a serious addict!

 

I hadnt thought about the dew point thing but it makes sence, guess I just have to live with it. Ill try the anti fog stuff and see what happens.

First time Ive lived in the South and had to deal with this much humidity.

Stan Francis - I havent made it to Lake Charles yet but it would be great to have a tour guide.

Thanks

Smiley

 

I'm a flight officer in the Navy, so my entire aviation career has been in the E-2C "Hawkeye", doing airborne command-and-control, and all of my squadrons (and most of my flight hours) have been in the Norfolk, Virginia area.

I'm only here in California to attend the Naval Postgraduate School for the next two years, getting a Master's degree in Applied Physics.

 

Ahhh...much more serious flying!

 

What about the, er, "palmetto bugs?"

 

Here's something you might not want to do in Louisiana, but should work: Blast your defroster on high heat!

Actually, if you bring your windshield up to ambient air temperature, it should prevent the fogging, but then will it cool back down while driving and start fogging? I'm wondering whether it's something you could do once when you set out, and if the effect would then last for the rest of the trip.

 

I tried that, but I could not stand it long enough to do any good

Way to hot for any kind of extra heat in the car

Smiley