Weather can cause a lot of trouble. Driving in bad weather usually causes a lot of problems. Luckily there are many things you can do as a responsible and safe driver.

Reading this article is an excellent first step to find out things. Especially for the question “why does my windshield fog up”. Ever thought about why does my windshield fog up when I turn the heat on? Or if I blast the A/C? Well, read on my friend. We explain.

why does my windshield fog up

You may notice in uncomfortable weather when you initially get into your car the windows fog up.

Maybe your dog is panting up a storm and the windows look like your mirror after a hot steamy shower. Whatever the case you may ask yourself:

Why Does My Windshield Fog Up?

Windows fog up because there is a temperature difference between the inside and outside of the car. The cooler and dryer side cools the windowpane down. When the warmer humid side touches the chilled window it makes fog!

Essentially condensation builds up when the liquid contained in the warmer air cools to the cold dry air temperature (or the warmer airdrops to the dew point; air creates dew!).


Preparation Kills Condensationwhy does my windshield fog up

On a whim, you can try using an ammonia-based glass cleaner. It removes small specks on the window that love to collect water vapor. Less vapor means less fog outside. These types of cleaners are readily available at most pharmacies, auto stores, supermarkets, and at some gas stations.

Use a product like Anti-Fog on the inside of your windows. It is basically a wax type product that is very slippery so water droplets cannot stick to it. Anti-Fog goes on clear and is undetectable when driving. It usually lasts days or weeks but it provides amazing results when used properly.why does my windshield fog up

When in use with RainX the two will keep your windows extremely clear. With RainX there are times you don’t need your wipers in the rain!

No Anti-Fog?

Why Does My Windshield Fog Up On The Inside In Cold Weather?

When it is cold outside and your car is fogging up you will want to turn the heat on. The cold dry outside air cools the windows. When the more humid and warmer inside air touches the cooled windows it makes the windows fog inside (condensation build-up).

There are some things you can do:

why does my windshield fog up

  • Crack the windows and blast the heat. It will make the car comfortable while letting the cool dryer outside air in for the stuffy inside air.
  • With the windows rolled up blast the heat for a few seconds until fully hot. Turn on the defrost setting. If nothing happens switch to A/C and let it pull the heat away from the windows. Turn off recirculation and let it sit like that for a bit.
  • If your car is a bit older and the defrost doesn’t work too well you can use a rag to wipe the windshield to get rid of the majority of the moisture then try one of the two tactics.

Why Does My Windshield Fog Up On The Outside Of My Car In Warm Weather? 

When you’re in a warmer climate or summer is here you will undoubtedly blast the A/C. Your car will be hot and it’s comfortable for no one. But now there is fog outside the windshield? What the hell? What can I do now?

Try This:
  • Roll the windows down a bit or all the way depending on your comfort level. This can get uncomfortable quickly.
  • Windshield wipers work quickly.
  • For a quick and dirty clean up on the side windows wipe with a rag or simply roll the windows down and up.
  • Use the A/C in its weakest setting with recirculation off letting in outside air. This will keep the humid levels similar so the imbalance doesn’t create fog outside.
  • Windows will eventually dry off if you hit the freeway but it may take time.

Should I Warm Up My Car Before Taking Off?

why does my windshield fog upGiving your car a chance to warm up is a great way to make the start of your journey as safe as possible.

On older cars, if you let it rest at idle for a few minutes it may extend the life of your engine. The oil can move through the engine block. The friction will make it more viscous. When you finally take off that extra little bit of stress from the thicker oil will be minimized. Everything works harder at idle so it can work easier when the engine is pushing that steel wagon. It can make a big difference over the long run.

On newer cars with a large engine, it makes sense to warm the car up for up to a minute sometimes. Larger engines take longer to warm up than smaller engines. Warm it up to get the heat ready or blast the A/C to flush the desert burning air out the cabin. That way you can get on the road in ideal driving comfort and enough visibility to not do anything too foolish.


Driving in crummy weather sucks. It is uncomfortable and can be dangerous. I live in California and with the first sign of rain, drivers seem to lose their minds. All sense of order is gone and a freeway commute starts to resemble Mad Max rather than an orderly march down the wet paved road.

If you are properly prepared foggy windows don’t have to be dangerous. Limiting your vision with foggy windows is a sure-fire way to get yourself into an accident. Imagine driving down the road struggling wiwhy does my windshield fog upth the defrost squinting through the windshield holding your morning coffee.

Now think about the same person doing the same thing in the next lane over or even someone driving towards you head-on with the same extremely limited visibility. That can be a recipe for disaster. Luckily there are many ways to avoid this. some are cheap and some are free. You will only have to pay in minutes of your day. It can be inconvenient but it can be much more convenient than an accident.

We have discussed some sure-fire ways to minimize or even eliminate foggy windows. Weather happens. Fortunately, nowadays we don’t have to yield to it. We can fight it!

Have an easier way that we didn’t discuss? Leave it in the comments for other readers to try!

Thanks for reading and stay dirty.