This might be a silly thread but I just washed my car for the first time in an underground at my condo and noticed when I opened up the car after the windshield and windows at A LOT of condensation and it was very very humid inside. It's fairly hot outside at 28C and not much cooler in the under ground plus its rather muggy, so I'm sure it was the difference in the temp from inside the car to outside while washing it, but I've never had this issue with my previous w204 c63. The roof and doors were all closed of course, and there is no leaks or damp interior other than the condensation. Is this just the nature of a pano roof? Hopefully this doesn't happen when it sits in the rain, i guess I'll know pretty quick with living in Vancouver...


The exterior of the windshield is dry in the picture, so the condensation you're seeing is inside the windshield. Not the best picture but it's not just steam it's actually wet and dripping.

 

My 2017 has the same issue every time I wash it.

Not really sure if this is a common issue, or maybe we have some bad seals?

B

 

well for condensation you need a cold surface and moist air.
The dew point temp is when it starts to condensate on these cold surfaces.

SO either the water you used to wash was very cold (colder then dew point inside car) or excess moisture inside that increases the dew point above the hose water temp...

Not sure enough room inside car to swing a dew point thermometer....(maybe they have electronic ones now?)

So issue is excess moisture inside or very cold hose water.

 

With warmer temperatures (and ignoring large air mass changes like a cool/warm front moving through), you will get higher dew points. A dew point is the temperature at which, given the amount of humidity in the air, the air has contracted down from cooling (as things get cooler, they shrink/contract/condense) that it no longer has anymore open space to absorbe more moisture. Because of that, this excess moisture that is not absorbed instead forms dew.

As temperatures increase during the day, this dew point stays the same, as does the amount of moisture in the air. Yes, the relative humidity goes down as air temperatures warm up, but the actual amount of moisture in the air is (theoretically) the same. Relative humidity is a percentage that reflects the amount of moisture-absorbing space within the air that is actually taken up by moisture. If it's full of moisture, 100% relatibe humidity. If 1/2 of that space it take up by moisture, its 50% relative humidity. If no moisture is present, 0% relative humidity.

As air expands as temperatures increase during the day, more space for moisture is available. But if actual humidity stays the same (as in no moisture is added or removed), then the relative humidity goes down. You will get your lowest relative humidity at the high temperature during the day and your highest relative humdity at the low temp. But even though this percentage keeps changing, remember that the actual amount of moisture in the air has not changed.

Now, to your situation. You are running a hose, so you are adding moisture to the environment and thus increasing the actual humidity. This results in an increase in the dew point. I'm willing to bet that you had hot air inside the car that felt dry at those high temps and added moisture to the inside of the car while the temps were still high, raising the actual humidity and ultimately also the dew point. This easily could happen by opening the door while the ground is wet all around the car and then shutting the car doir again. Or maybe your vents for the A/C are open. You have air inside the car that can handle more moisture (higher temp, therefore more open space for water to be added), and as this space is filled with additional moisture it results in a higher dew point inside than the outside air.

As long as you are taking a car from high(er) afternoon temps and quickly introducing moisture at lower temps, this inside condensation can easily happen.

 

The tap water is indeed cold, it's just weird none of the three cars I had in the past with sun roofs had the same issue. Makes me believe that the pano roof being bigger some how contributes to it. I left my windows cracked and the sunroof cracked after I dried the car off for the car to air out after. I guess it's not a big deal as long as it doesn't happen when the car sits in the rain. I'm just a week into ownership though, so it was a bit of a suprise. Hopefully my weekly washing doesn't lead to any mold issues or anything.