Xantia misted

[Stickyfinger]

Afternoon chaps/chap'ss's

I was driving along all happy in the rain, all OK, demist vents set on foot/screen and 1/2 warm, air from outside. The road was wet from the rain, I then drove over some running water (not a puddle) and Woosh, all misted in an instant ! Later down the road, same thing and zero problems

Now this has me perplexed

[bobins]

I'm guessing your windows hit dewpoint for a short while.
If you keep the following in your head whilst driving along you should be able to predict if/when it's next going to happen


Relative humidity gives the ratio of how much moisture the air is holding to how much moisture it could hold at a given temperature.

This can be expressed in terms of vapor pressure and saturation vapor pressure:

RH = 100% x (E/Es)

where, according to an approximation of the Clausius-Clapeyron equation:

E = E0 x exp[(L/Rv) x {(1/T0) - (1/Td)}] and

Es = E0 x exp[(L/Rv) x {(1/T0) - (1/T)}]

where E0 = 0.611 kPa, (L/Rv) = 5423 K (in Kelvin, over a flat surface of water), T0 = 273 K (Kelvin)

and T is temperature (in Kelvin), and Td is dew point temperature (also in Kelvin).

So, if you know the temperature, you can solve for Es, and substitute the equation for E into the expression for relative humidity and solve for Td (dew point).

If you are interested in a simpler calculation that gives an approximation of dew point temperature if you know the observed temperature and relative humidity, the following formula was proposed in a 2005 article by Mark G. Lawrence in the Bulletin of the American Meteorological Society:

Td = T - ((100 - RH)/5.)

where Td is dew point temperature (in degrees Celsius), T is observed temperature (in degrees Celsius), and RH is relative humidity (in percent).
https://iridl.ldeo.columbia.edu/dochelp ... point.html

https://en.wikipedia.org/wiki/Dew_point

[CitroJim]

In my experience the Xantia is the worst car I've ever known for misting up... They'll do it at the drop of a hat...

My Activa was the worst of all...

[Stickyfinger]

Bobins, cheers for that

Jim, my car normally does not mist up and that is why I wonder where the sudden increase in moisture came from.

[xf1ref]

It happened to me after a heavy summer rain and only the AC solved the problem. Another phenomenon on hot summer days when the humidity is very high and the windscreen is misted outside due to AC...only wipers can solve this.

[Stickyfinger]

but but but, where did the sudden rise in the moisture come from ? It was not like it was a puddle or was dry on the road, just a patch of running water on an already very wet road which was under the front wheels.
As there is no air intake down there I am still confused as why it happened (it was extensive) and needed the window cracked open and fan on full to clear it.

[momag46]

Also...

If the inside of the screen in not clean the moisture has something to settle on

Air con helps to dry the screen but can also create the misting on the outside. I used to get this on the later C4 and finished up using Rainx, but as we know that can have it’s own problems (please don’t start on that one again ).

Maurice

[Hell Razor5543]

I used to get this on the later C4 and finished up using Rainx, but as we know that can have it’s own problems (please don’t start on that one again ).

Maurice

Alright, I won't!

I do agree that, getting the glass as clean as possible (inside and out) can help a lot, as that way you remove any 'seed' points for the condensation to form.

[CitroJim]

I do agree that, getting the glass as clean as possible (inside and out) can help a lot, as that way you remove any 'seed' points for the condensation to form.

Yes, I agree too... Keeping the glass as clean as possible really, really does make a difference...

I use a good electronics grade solvent and spotlessly clean lint-free cloths to get the glass squeaky clean... I repeat this as an when needed - every couple of months or so...

[bobins]

The external temperature right at the spot where the running water was may have dropped the temperature of the glass just enough to reach dew point on the glass so any moisture already in the cabin condensed out on the glass. The temperature only needs to change half a degree or so and that's enough in the right circumstances. I get this happening an awful lot in my truck on my way to work - there's just one spot in the countryside going through a small hamlet where my door mirrors will instantly mist over and I have to use the demister to clear them. It never happens anywhere else on my 10 mile commute.
I blame global warming

[ekjdm14]

I used to get this on the later C4 and finished up using Rainx, but as we know that can have it’s own problems (please don’t start on that one again ).

Maurice

Alright, I won't!

I do agree that, getting the glass as clean as possible (inside and out) can help a lot, as that way you remove any 'seed' points for the condensation to form.

Did I miss this one? I don't like Rainx at all, in the dry it seems to leave the 'screen less clear than it otherwise would be (it takes on a kind of oily shimmer, almost as if the car's about to suffer a migraine!) and in the wet it's OK above a certain speed where the water beads get blown away, anything below that though you end up with multiple distracting beads just sat on the 'screen & would need to use the wipers anyway (perhaps more frequently than if the beads had stayed larger and fewer as with clean glass)... IMO there's nothing wrong with keeping the windows clean and using the wipers as they're intended, in good condition they work better than any snake oil...

Bikes, mind, are a different matter and a dash of Rainx on the outside of a visor coupled with a squirt of Bob Heath anti-mist spray on the inside can make the difference between a safe ride and a trip to A&E.

Sorry...

[c.morewood]

Stickyfinger, In my experience if my Xantia mists up inside, there is some water lying somewhere in the car. If there's no water in the tailgate/boot then look under carpet under the rear seat, if no joy there, then at the passenger side footwell. Don't just feel the carpet, take the door seal trim of and lift the carpet. Feel along tothe front of the footwell till you reach the plastic section running across the footwell and the foam under it. If that is dry all is well butt, if like me it is damp then you have an unidentified leak. I've beem looking for it all winter and now even after a new windscreen its still damp. (check the driver side as well)
Hope thats of use.

[Stickyfinger]

Carpets and foam all dry. A couple of weeks ago I found the rear lamp clusters were leaking a bit (damp boot) but the carpet/underlay were not in the car and the carpets etc in the back were dry.

[Michel]

Bikes, mind, are a different matter and a dash of Rainx on the outside of a visor coupled with a squirt of Bob Heath anti-mist spray on the inside can make the difference between a safe ride and a trip to A&E.

Sorry...

Ugh no. I'd not put rain-x on any of my visors. Tried it once, it was horrible in the dry. I use a pinlock visor insert which completely stops misting and I've only had vision problems when it's been snowing!

[c.morewood]

Carpets and foam all dry. A couple of weeks ago I found the rear lamp clusters were leaking a bit (damp boot) but the carpet/underlay were not in the car and the carpets etc in the back were dry.

Fantastic! Glad you found the cause.. I'm still trying to dry mine out after 3 weeks ...I must get the aircon working again