Leaks

Technical Information and Restoration Parts for the 928

So your 928 leaks?

There is a simple solution to this problem. Do not wash or drive the car in the rain. Even though the 928 was Porsche designed from the ground up, many Porsche owners, due to engine placement, do not consider the 928 a "real" Porsche. However, when it comes to leaks the 928 upholds a long and fine tradition of Porsche cars doubling as bathtubs. I know one 912 owner who used powered food colors to track down leaks. I do not think it worked.

Here I will cover some of the more common sources of leaks on the 928. Ideas and contributions are of course welcome.

Heater Drain. The drain under the HVAC fan is probably one of the most commonly over looked design flaws and maintenance items on the 928. Just below the air cleaner on the passenger's side is a rubber flap. The flap drains water that passes into the car from behind the hood. Unfortunately, the vent gap behind the hood is big enough for dirt and leaves to accumulate. Eventually enough material accumulates and blocks the drain. As water is prevented from draining it builds up and over flows into the passenger foot well flowing over the fuse / relay panel and accumulating in the foam sponge under the floor carpet.

The cure is to clean out the area under the fan. Sometimes most of the debris can be cleaned by removing the rubber flap and using a coat hanger and compressed air. In extreme cases the fan can be removed to gain access. In this case it is a good idea to use a vacuum to clean the A/C evaporator core. There is also the possibility of the chassis rusting away causing permanent leaks.

Sun Roof. Like the external HVAC unit the sunroof is designed to leak. There is a trough around the inside of the sunroof frame designed to catch the water and drain it out at the four corners. Each corner is connected to a plastic tube. Two of the tubes run down the A pillar and out under the back part of the front fender. The other two drain out through two holes in the hatch recess area. Lifting the hatch and looking up near the corners of the roof will locate the holes.

The easiest way to clean these drains is with a piece of weed whacker line. The drains can be tested by filling the channel with water. Water should drain freely and run out the drains. There are other factors beyond clearing the drains. The metal channel attaches to plastic tubes. These tubes can be punctured if cleaned too aggressively. If water drains inside of the car when testing the sun roof then the headline has to be removed and the plastic tubes replaced.

There is another place for water to leak in from the sunroof area. The tracks the sunroof glides on (well should glide on if they are cleaned lubricated) are sealed from the body. If the tracks have been removed and not resealed properly then water from the channel can seep under the channel and into the cabin. Since the headliner is sealed to the sunroof channels water will follow the head liner and fall on the rear seats.

Roof Leaks. The roof channels are pressure fitted to the roof and held in place with a small clip at the end. The clip is held in place with a Phillips screw. To seal water out the clip is bedded with windshield sealant. Often this sealant is removed when working in this area causing water to follow the threads and leak into the rear of the car.

The rear hatch hinges are mounted in the same bedding compound. Again water can leak in under the hinges.

The 928 is designed for a roof mounted ski rack. The rack mounts to the side channels and is held on place with two bolts on the inside channel of the rear hatch. When the rack is not installed four plastic bolts, two on each side, are installed to prevent water from finding its way into the bolt holes. Sometimes these are removed or not well sealed and water leaks into the cabin from this area. Not every year uses the same size threads.

Rear Hatch Leaks. The hatch is sealed with a single gasket running around the entire hatch area. The rear corners of the gasket can split ruining the seal. The gasket itself can shrink with age causing leaks. Another issue involves the rear hatch lock. The tongue in the lock is made of plastic. Over time through closures and vibration the plastic wears causing the hatch to ride high in the rear breaking the seal with the hatch gasket.

The rear hatch window is held in place with a flexible window seal just like the windshield and with some plastic clips that serve the dual purpose of avoiding the Avanti flaw of the rear window popping out at high speeds and holding the trim in place. These clips are bedded in the same window compound sealing and a red paper washer. Any one of these clips is a potential leak.

The S spoiler is held in place with bolts going into the same channel replacing the trim on the earlier models. These bolt holes are potential sources of leaks. The S spoiler acts as a dam trapping water. There are drain channels that allow the water to drain off the window and down the back of the hatch. Failure to clean these drains causes the hatch to rust and rear body to rust opening up holes for water leaks.

The hatch gasket is push pressure fit to a lip in the hatch channel. It is possible for water to creep up under the gasket and leak into the cabin. Further exacerbating this is the accumulating of debris and leaves on the top edge of the hatch. This can trap water in the area causing water to find its way in both under and over the gasket. A note on this. A gasket to seal must be clean. Over time dirt accumulates on the surface of the gasket and water follows the dirt. I found this out the hard way when installing skylights without adequately cleaning the dust off the glass. When installing a new gasket the hatch should be removed and the top part of the gasket sealed with silicon or flexible windshield sealer.

Rear Quarter Windows. The gaskets around the rear quarter windows can leak. It took me a little while to track this one down. The gaskets are sealed to the body on installation, but the gaskets are expected to self seal to the glass. However this does not happen. Water contrary to popular belief can run up hill often due to pressure differentials. Water flows from the rear of the quarter windows under the window glass and up over the inside of the gasket and then down inside the rear quarter panels and either under the rear seat bottoms or into the tire well. The rear seats make excellent sponges. I cut the tip of a clear silicon tube and attached a thin straw forcing silicon down between the glass and gasket. After it dried I used a razor blade to cut away the excess.

Windshield. The windshield is held in place with flexible windshield sealer. It is possible for the windshield to not be seated right on installation. Given a thin windshield it is common for the 928 to have more than one windshield in its life. Leaks from the windshield area are easy to detect and easier to fix with black silicon purchased from the hardware store. However, at times the windshield will not leak water but still leak air. If you are getting some wind noise in the cabin this is a good place to look.

Side Windows. Again the windows on the doors are designed to leak. The seal at the bottom of the window, like the seal on the sunroof, is intended to keep the majority of water from leaking inside the door. What water does leak inside the door is drained out the bottom by some weep holes. The weep holes can become clogged and the gasket rots with time causing excess water to get into the door. The excess moisture can condense inside the car dripping down into the back seat. The window motors and other components in the door can corrode and fail as a result of the excess moisture.

There is a vapor barrier under the door panel to protect the backing of the door panel and interior. When this vapor barrier is penetrated from removing the door panels many times this protection is lost. Replacing the lower window seal when rebuilding the window guides and insuring the vapor barrier is sealed the windows will work as new. the door panels will not warp or rot at the bottoms and the interior will not get as much condensation.

Alternator. While not a leak issue the alternator is still an issue of water damage. On the older cars the failure to use the snorkel / vent tube allows water to short out the diodes in the back of the alternator. It seems the newer alternators from 85 up are more stable and not as prone to burn out when flooded with water. The best cure is to install a Delco replacement and just eliminate the snorkel tube.