ianw

My recently acquired 1990 964 (no aircon) seems prone to 'steaming up' unless the heater is on full demist.

(Am in Scotland, yes its a damp climate; no, the car is NOT leaking or damp inside.) Other similar age of vehicles are not showing same problem.

info:
Car recently had new hot air duct pipes fitted from heat exchangers to cure low heat output problems found to be leaky duct pipes.

Seems the air from the heater / demister may be moist? Is this possible? How?

Tried rain-x etc, not much better.

C4TT

I would let the car sit in the sun for a while if that's an option. I would also use desacant inside the car to absorb any excess moisture...
You can even try a blow dryer for to get panels that may have trapped moisture...

This is pretty common with the older cars, and a tough battle...

Good luck, and I would love to hear other solutions...

warmfuzzies

Ian,

Have you made sure the vent controls all work properly? I know they are a pain to decipher and I'm always forgetting which slide does what, but whenever mine mists up, (usually when I first start the old girl) I push the full demist button which diverts all air to the screen, have the rear window heater on, then after the screen clears, make sure most of the air goes to centre vents/windscreen and this keeps mine clear in all conditions.
I usually keep the heater control at 21 degrees or thereabouts.
Kevin

tonytaylor

Pull the carpets up and have a look at the foam sound proofing underneath - it can hold a staggering amount of water. Obviously this can cause high humidity.

C4TT

I had a leak, which soaked the foam under the front carpets so bad, I had to toss it out.. I dried the car for days with fans, heaters, blow dryers etc... and was able to prevent rust. But now when I store the car, I leave desecant in there to absorb any stray moisture.

robmug

It sounds like there's a lot of water inside the car somewhere...insulation under the carpets is the best start point.

You said RainX doesn't work - have you tried RainX anti fog? I use this on the insides of my windows and haven't had any misting at all over the last few weeks...

Fred, Long Island

Given the age of the car....your windshield probably weeps.
It creeps down the bulkhead up above your knees.
A very subtle, hard to find leak. You have to remove the carpet off the bulkhead and peer up into the chamber to see it.
Let us know if the soundproofing on the floor is wet.
Good hunting.

Cuppie

Moisture in the heat exchangers.

Mel

springer3

Does it mist if the car is left standing, or only if you are driving? Your breath puts a lot of hot steam into the compartment. If it is cold outside, you will get condensation. Your other cars that don't fog may have more outside air flow. I am not sure how the fresh air vent operates, but there is a recirculation switch. It could be that the flap is stuck in "recirc" mode.

Let us know what you find.

ian c - u.k

not sure how long it takes , but i have heard of classic car restorers , placing the cars into the paint baking oven , to dry it out before they start work !!

if the car is garaged overnight , you can buy a delonghi (or similar) de-humidifier , and open all the car apertures , and close all the garage apertures !!

as long as the storage area is dry , this has the same effect as a " car-coon " device

ianw

Lots of good pointers guys... but:

1. Undercarpet sounproofing is bone dry.
2. Have a dehumidifyer unit that I left on in the C4 for 3 days ... zero water gathered (it does work, use in my boat and collects h20 v well!)
3. car is garaged most of time
3. still feel moinsture is coming in via the vents! Drove her home tonight, dry 12 deg C day, no real misting... parked in drive, came out an hour later, and inside wind screen is partly misted above vents!!

mmmm.. the ' moisture in heat exchangers sounds on track....

Ian

ianw

.. and will check if recirculate button/flap stuck... thanks

mojorizing

Springer3 has got a good answer...the car might be in recirc mode. Check that the center servo has it's linkage pushed all the way to the rear, that's the position it's in when in full outside air/ no recirc.

ianw

....take it back - lifted all 3 layers of flooring to find wet foam!!

Drying out and preparing to leak trace....

Also noticed rear hood / bonnet rubbers not stuck down , see separate posting - may these lead to water leaking into luggage bay/ down over footwells?