Air rushing in under dash

[cirrus]

Please excuse my ignorance - new to Porsche. I've just bought a very nice 1969 2.0T Targa that has been mostly restored. One problem - when I get up to about 50mph there is air rushing in under the dash top making a heck of a noise. It's very difficult to see why without dismantling the dash (which means taking out the windscreen, I believe). Any thoughts on what this could be?
Cheers and thanks for your help.

[Bummler]

I know this perhaps sounds silly but is the hood completely closed when driving?

After hitting a pothole or particularly big bump short hoods have a tendency to pop the hood open when the latch mechanism is out of adjustment. I've noticed increased air flow out from under the dash when this happens on mine.

Just a thought...

[RickS]

It appears you have an air leak into your trunk exiting through the dash. How is your weather stripping around the trunk? How are the gaps were the trunk mates to the fenders, etc? Did the car previously have AC? If so there are a number of holes which may be the culprit - under the hole for the windshield washer bottle, and the smugglers box.

[cirrus]

Thanks for ther suggestions! The hood is closing ok but I have noticed various holes between trunk and dash where air could be coming in. There is also a hold at the bottom of the smuggler's box which isn't good. What is the purpose of the box btw? Cheers!

[cirrus]

Pic of my car!

[davep]

Check your VIN tag (like this one) to see if you have the 911 ~ S66 in the upper right corner. That is for the Webasto gas heater the compartment was designed for:

[Bobs 67S]

Cirrus
start with eliminating the source of the air infiltration.

Use low tack tape (blue painters tape) and seal the four sides of your front hood.
Also cover the air vent above the hood at the cowl. Make them air tight.
Drive the car at speed.

If this stops the air leak, good. we'll come back to the fix below.

If the air leak is still present it could be
A, the openings where the gas heater was removed - exhaust hole in the floor, and open heater duct aimed at the gas pedal area. Look in that compartment below the door in the trunk (smugglers box).
B, there are louvers in the inner fender - opening from the wheel house for gas heater fresh air - If the opening into the passenger compartment are closed this area is not a concern remaining open.
C, Are proper seals around the shift rod at the rear of the center tunnel?
D. Are the plugs in the front latch panel missing - access to the bumper-ettes bolts.
E. the heater tubes coming thru the rocker panels -potential rust openings.
F. Check for rust opening at the battery boxes or the front pan.
G. Check for rust into the center tunnel thru the pan floor

Getting back to the most likely source - the hood area.
Test your front hood seal: open the hood place a single piece of paper say 3" x 6" (a dollar bill) over the seal - shut the hood an pull the paper out. Does it just fall out or is there resistance. It should have a snug tug to remove it. Repeat this test all around the seal. if it pulls out with little or no resistance there are air gaps and is more than likely the start of your problem. Talk to your body guy as to the best remedy for seal gap - replace with the correct seal - tap up the seal rail - lower the hood - etc. or all of the above.

If the hood seal is good - move on to:
There is a flap seal into your fresh air vent at the cowl ( that slim grille above the
hood) the seal could be gone or rust has perforated the side walls. Check the operation if the flap or it's operation cable could be froze open. Verify they are moving and close. Flashlight and mirror check the seals.

Check the paper covered ducts in the corners of the trunk, air vents to the corner of the windshield, are they broken? Check their cover seals - from the inside of the car, look up under the dash, next to the fenders - if they are missing this is a large air infiltration area. Temporary fix is a closed cell soft sponge, or use the super soft open cell ones that are sold at your car parts store. Just stuff them into the holes.

Has there been any after market items removed and left large holes in the front fire wall? Look behind the carpet and foot rest panels for holes.

Has there been holes prior drilled for car alarms, speaker wires etc into the trunk? into the wheel wells? the floor?

Prior drilled holes can be temporarily filled with the aluminum duct seal tape. Any of the fiber board and foam seals can be replicated or replaced. The paper ducts can be sourced thru Pelican.

Let us know what you find. What was your fix?

[naparsei]

Is your fan on "high"?

[cirrus]

Wow! Thanks guys, esp Bob 67S. A good weekend's work coming up!

[Haasman]

Cirrus- Did you ever determine the source of the air coming into the cabin?