Had same problem with a Fiat Uno. Firewall punched for RHD or LHD,
with plugs, plates, and blind grommets in the unused holes. Some plugs
were firtreee with mush heads, and in the wrong way round, mush head
on the inside, not the engine side. So drive in the rain and water
saturated the carpet. Apart from replacing them the right way round,
and some were hard to get at from the engine side, I made with
some glass fibre to seal things up good and proper. Also had boot
flooding problems but that's another story and cure.
I had a car flood after the drainage from the chaber with the heater intake
became partially blocked, in a storm the water filled the chamber and came
in through the heater intake. I found two inches of water in the footwell.
If there's water in there or it drains slowly you got a blockage, it may be
visible & easily cleared or you may have to use a pipe cleaner to clear it.
These are always tricky.
First clue is what type of carpet?
In my expereience most Fiats are fitted with 100% waterproof carpets. To
fiind this out you really need to examine the backing of the carpet. In the
waterproof ones the whole backing is a plastic/pvc sheet.
If the waterproof type then unless the water level in the floor of the car
(floorpan) has come high enough to breach a hole or cutting in the carpet,
e.g. where the lower seatbelt mounting bolts on the inner side sills pass
through the carpet, the leak must be dripping/running/flooding onto the
upper surface of the carpet.
Another check is to remove the driver and passenger front/rear door tread
strips/moulding and lift and feel the floor and felt underlay. If they are
dry then the leak is coming onto the top surface of the carpet.
It is a hard long process of elimination. Water ingress is a real bummer.
Does the car have a sun roof? Are the drain holes blocked?
Is the car parked on a slope?
Any signs of damp/staining round the glass areas.
Three examples of ingress that I have debugged may give you some clues as to
'how to think like water'.
1) Fiat Coupe. On the doors there is a black moulding on the inside of the
door around the lock area. I was experiencing water in the rear footwell.
In this case water was running down the outer edges of the door apperature
seal till it met the plastic moulding. This left a little step where the
moulding cross at 90 degress the door seal. In warm wet weather not a
problem. In cold wet weather this 'step' would not tightly hug the moulding
so the water ran down the outside of the weather seal to the moulding, then
ran along the moulding seal interface to traverse the weather stip and then
carried on running down the inside of the weather strip, onto the tread
plate and onto the top of the carpet.
2) Fiat Uno. 'A' posts (the front post that the door are bolted to) are
hollow. By design they drain into the sills and out of the sill drain
holes. Look behind any car door and you will see that where the hinges bolt
to the main bodywork and where the door straps locate there is plenty of
opportunity for water to naturally penetrate these areas. In my case, when
I parked the car on our drive (in one position which was inclined & tilted)
I would get water in the floorpan beneath the carpet. Took me months to
figure out that the problem only occurred in this parking position and not
in any of the other three places I could park. In the inclined and tiled
position water that entered behind the out door edges was safely running
down the 'A' and 'B' post external reacceses. However on the 'A' post it
was entering the door strap hole, running down the inside of the 'A' post
(no problem as it will drain out of the sill). BUT sadly on its way down it
hit the wiring loom for the central locking and electric windows and ran
along the loom to the inner inside of the 'A' post, entered the car and
continued to run down the 'A' post and under the carpet on the inside of the
car! Solution was easy but rather fiddlely!. Tease excess loom wiring out
of the door and the car to create a 'drip loop' inside the 'A' post.
3) Fiat Tempra. Sun roof. Water in passenger floor pan. Water appears to
drain away from the sun roof try to the underside the car as expect. Well
most did. The windscreen pillars were foam filled after the sun roof and
drain hoses, which run down the windreen pillars, were fitted. However the
internal the internal pillar tim is fitted afterwards. One of the trim pegs
had punctured the soft drain hose, (which was now firmly held in place by
the expanded foam against the inside of the window pillar), and water
traversed the 'peg' to the inside of the car and behind the windscreen
pillar trim. From there it was another hidden trip into the floorpan!
Sorry I can't answer you question directly other than to say 'imagine you
are water' and do forensic like examination of the crime scene, feeling
touching, looking, smelling etc. for traces of anything you wouldn't expect.
Also car postiion, weather, temperature etc.
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