XJ6 S3 plenum chamber pic/drawing

(zenit) #1

I think the plenum chamber drain valve might be blocked in my xj6 s3, as I am getting water into the footwell on both sides of the car. Does anybody have any pictures or drawing of the physically location /route of the drainage hoses/duckbill etc.


(David Jauch) #2

Do you mean that you get wet feet in turns? It’s not a valve, it is two white plastic tubes exiting left and right of the gearbox tunnel. You‘d be able to see them if you removed the cheek panels (where the footwell vents are).

The other chamber is below the grille in the cowl and the two big drains exit into the engine bay. Those won’t give you wet feet.

If you don’t get wet feet on turns your windshield seal might let water in which is apparently common.
You could run a few trials with a garden hose if unclogging the drains doesn’t help.


(zenit) #3

Thanks. It happens without turns. I took it to a panel shop and they taped up the top of the plenum chamber and ran water over the windscreen and no water came in. They then ran water into the plenum chamber and it leaked. So does that sound like the white plastic tubes or is it more likely to be rust hole/s in the firewall?

The panel guy said I would have to remove the whole dash to see what is going on, bit reluctant to do that until I’ve check it out as best I can.

(Dwomby) #4

If they want to check the plenum for leaks, surely they can drop a mirror on a stick (or a camera) in there to look at the interior? Anyway, here’s a diagram of the duckbills etc. for an S2. I expect the S3 is the same.


(zenit) #5

Thanks for the diagram. Yes, I’m taking what they said with a grain of salt. Tomorrow I will check out the chamber with some mirrors, as well as check for any blockages. I think they where not that interested in finding the exact cause of the leak.

(Jochen Glöckner) #6


not sure about your concrete plans, so just to make sure: you can remove the vent cowl grille by simply prising it off - just be very careful not to break the tabs.

Once the grille is off you might get yourself an empty beer crate or something similar to step on and get closer to the vent cowl, and a flash light and you can see pretty much everything inside, in particular whether there is rust damage. BTW, while you’re there anyhow you might use a can of AC cleaner and run it through the heating and ventilation system - made a big difference for me.

Good luck


75 XJ6L 4.2 auto (UK spec)

(Paul M. Novak) #7

If you search the Jag-Lovers archives for “duck bill drains” you will find that others have posted about discovering a bunch of debris in the plenum that blocked the drains and backed up water inside the plenum. The only place the trapped water could go was through the fresh air intake flaps for the heater blower motors and then onto the floor. Check that there is no debris in the plenum and that the duck bill drains are clear by pourine some water in the plenum to see if it drains properly.

I don’t really understand how debris can get through the air grille screen, but perhaps if the car was parked outside under a tree maybe that caused small debris to accumulate in the plenum over time.


(Frank Andersen) #8

Another source of ‘wet feet’ is the AC water drain, Andrew…

The air humidity is condensed by the cold evaporator. The collected water is drained by tubes exiting on either side of the gearbox. If these drains are clogged; prodding will provide a solution - and a gush of water…:slight_smile:

As an aside; a leaking windscreen will also wet you feet - the garden hose test may reveal such a problem. But it is important to locate the source of the leak by visual inspection…

xj6 85 Sov Europe (UK/NZ)

(David Jauch) #9

You will find that in my first response. Let me add that I had wet feet after rain, and that my AC was disabled at that time, so water will end up in the unit even though the cowl is clean and the large rubber drains in the engine bay are open. I rodded out the two drains over the gearbox with success.

(zenit) #10

Thanks David and Frank,

The air conditioner on the car has not been running for over 10 years but all the hardware is their.

I checked out the plenum chamber it looks good, no rust, no debris and water flows out the 2 ducbkbill holes. One side does not have a duckbill and the other side does but it is dried up and busted up at the end. Is it worth getting new ones or is it one of things where it’s better without them?

What are the holes with a hinged flap at each end of the plenum chamber ? Are they air vents, and normally open?

I found the 2 drain pipes around the transmission, where does the other end of these pipes go to?
The car is going on the hoist in a weeks time to have a diff changeover, I will be able to have a good go at cleaning it then or can you get to it from the other end of the tubes?

(Frank Andersen) #11

Get new ones, Andrew…

The duckbills prevents air and debris/water being sucked into the plenum/car from the engine compartment.

The 2 drainpipes around the transmission goes into the ‘drip-tray’ under the evaporator - prod them open

xj6 85 Sov Europe (UK/NZ)