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Old 3rd November 2020, 16:39   #1
Blink
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Exclamation Rust warning - drain tube exit points

Keep a beady eye on this folks.

The two drain tubes that exit under the car (near the ABS modulator bracket on the LHS and the steering column UJ on the RHS) cause rust on the upper surface of the metal around the holes.

Here's the LH tube - I've pulled it out of the hole to show the problem.



The rubber tubes themselves are clear of debris btw so something funny is going on.

More pics later.
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Old 3rd November 2020, 19:17   #2
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.... More pics later.
Caught in the act - the RH tube with an actual drop of rain water.



I pushed this one in (up) and the whole of the upper surface of the metal is soaked with water. The seal on the tube stops it from escaping so the metal stays soaked.



I think the compartment that the tube is in is separated by a wall so the water is not getting as far as the steering column UJ area.

https://www.the75andztclub.co.uk/forum/showthread.php?t=256144&page=4

Last edited by Blink; 6th November 2020 at 17:53.. Reason: Link added
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Old 18th November 2020, 20:40   #3
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Lightbulb More pics

Here's another pic taken from under the car looking up through the hole in the LH lower plenum chamber (i.e. the tube exit hole)(which is out of focus). It shows there's rust around the hole in the upper chamber as well (i.e. the hole in the floor of the ECU/pollen filter chamber) .



This proves that water is running down the outside of the rubber drain tubes and causing rust around both the upper and the lower holes.



I whipped the cover off the LH plenum and here's the view looking down through the ECU/pollen chamber to the lower chamber beneath.





Here's the tube with the water trail (& muck) clearly visible on the outside.





It doesn't help that it's turned into an oval (!) when the hole it's supposed to fit is round.



So this is what's happening on the LH side: water runs off the windscreen and drains down under/through the foam strip that's supposed to seal the little plastic bulkhead thingy. Then it runs along the upper chamber floor behind the pollen filter and forward towards the hole. The oval rubber tube doesn't seal the round hole properly so water travels through to the lower chamber on the outside of the tube - it can't drain out through the exit hole so it just sits there.




Exactly the same thing happens on the RH side, except there's no plastic bulkhead because the wiper mechanism is in the way. I can't do anything about this side without taking the servo out - or taking the closing panel off.




The sealing /waterproofing of these plenums really is lousy!

Last edited by Blink; 18th November 2020 at 20:54..
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Old 18th November 2020, 23:43   #4
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I really like this pic.--Did you draw it yourself ???---

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Old 19th November 2020, 12:10   #5
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Blink

"The sealing /waterproofing of these plenums really is lousy!"

Could you do better? Design a mass production vehicle which remains completely rust proof 18 years later??
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Old 19th November 2020, 12:28   #6
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Default What if?

If a long rubber tube was bonded to the upper tube, and put through to the underside of the car it would stop any contact with the metal, that's provided a good seal is made at the top. The tubes could be also made slightly longer to give a better run off underneath.
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Old 19th November 2020, 13:22   #7
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I really like this pic.--Did you draw it yourself ???---
Thanks Jon - yes I drew it using a simple programme. Photoshop would have made a neater job (with edges of photo for instance) but it's much more complicated.
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Old 19th November 2020, 13:26   #8
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Blink

"The sealing /waterproofing of these plenums really is lousy!"

Could you do better? Design a mass production vehicle which remains completely rust proof 18 years later??
Yes.

It hasn't remained completely rustproof because there's rust in the drainage holes.
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Old 19th November 2020, 13:31   #9
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Originally Posted by Saga Lout View Post
If a long rubber tube was bonded to the upper tube, and put through to the underside of the car it would stop any contact with the metal,that's provided a good seal is made at the top. The tubes could be also made slightly longer to give a better run off underneath.
It would still be in contact with the hole in the floor of the upper chamber. Can you sketch it?
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Old 19th November 2020, 17:38   #10
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The existing drain tubes are only part of the problem unfortunately, the rust problem could be solved by removing them, acid treating the metal on both faces of the plenum holes, replacing them with a length of tubing that is fed through both holes to below the sub frame. The top of the tube secured to a short metal pipe that has a flared top face like an upside down top hat with the crown missing. This, sealant fixed, into the plenum floor, would guide water through both parts of the area and down to the ground. I find the biggest problem from water ingress to be what runs down the windscreen corners and is guided between the A post inner and the wing. this is supposed to exit the wheel arch behind the plastic liner. this it does but also deposits crud there making it a potential rust trap. takes much longer to deal with on a regular basis than rodding the plenum drain tubes.
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