Been playing in the puddles tonight and went through a long stretch of water but it was no more than a foot deep. Speed varied but around 15-20 mph. I considered this would be no issues for a TD5, but directly after that the engine seriously hesitated and slowed. A good bit of throttle cleared it, but was accompanied by a large amount of smoke from exhaust. No problem after that, but on returning home I checked the air filter and it was pretty wet. Guess I was lucky, but why did it take in water? One thing that does look suspect (apart from the driver) is the dump valve on the air filter. Should it be tightly closed under the wheel arch, as you can get your finger in mine without having to open it first? Any clues would be good....Thanks.

Straight from the ministry of cr-p design,the rubber thingy hangs down in the wheel arch,and takes on water.Think I'd change it if I was daft enough to buy one,seen this before - they do eat water but it cant be good,so either mod the dump valve or fit a new one.

Thanks mate - I take it they should be tighly closed when new?

Well it was made in Brum,seriously it should be shut - obviously not totally waterproof,its only going to be a couple of quid for a new one to compare it with.

The dump valve if clean on its lips only really works when the air is being sucked through as the vacuum closes it, however I had the same problem also would misfire at around 2-3k until water clear. Traced it to two things, one the foam gasket on the air intake bolted to the inner wing but the biggest being a small square opening on the bottom of the air box near the front besides the input housing. If you have the same you can spot the muddy water blasted up against the inlet housing. I made a silicone gasket for the inlet and epoxy resin the hole and no issues since.

Thanks for the tips - will have a good look when I get a moment.