Thread: Air filter flapper blowing air, 300tdi

Originally Posted by Oberon 110

Hi all,

I've noticed the drain valve flapper on the bottom of my air filter housing puffs air out at idle, and starts to close as RPM increases, staying fully shut at what I estimate to be 2kRPM. My understanding is that these valves stay shut when the engine is running and open when the engine is off to drain any water. That said, is it normal for them to puff at idle? My concern is that I've got timing issues - I've also noticed a bit of a knock and slight ticking, although one never knows if these sounds are normal or not on a tdi...

Any thoughts are much appreciated,
Cheers

If you are talking about the duck bill on the bottom of the air cleaner housing (same as heater air intake) it normally stays closed all the time and allows water or dust to exit if you give it a little squeeze. They are only around $5 new

Cheers

Originally Posted by travelrover

If you are talking about the duck bill on the bottom of the air cleaner housing (same as heater air intake) it normally stays closed all the time and allows water or dust to exit if you give it a little squeeze. They are only around $5 new

Cheers

Yeah thats the part. Even if it's old, air puffing out of it would mean pressure coming back through the air intake at some point, right? It's not just that it's open, but that air is puffing out of it at idle

Originally Posted by Oberon 110

Yeah thats the part. Even if it's old, air puffing out of it would mean pressure coming back through the air intake at some point, right? It's not just that it's open, but that air is puffing out of it at idle

That’s not normal, mine has nothing coming out of it normally. I have a relatively new one on now but the old one was often stuck closed. Need to give it a squeeze to clear.
Is it coming from the turbo direction or from atmosphere? Btw I just checked the price, it’s a hell of a lot more than $5 now, “Air Filter Cleaner Housing Dump Valve NRC8955”.

Originally Posted by travelrover

That’s not normal, mine has nothing coming out of it normally. I have a relatively new one on now but the old one was often stuck closed. Need to give it a squeeze to clear.
Is it coming from the turbo direction or from atmosphere? Btw I just checked the price, it’s a hell of a lot more than $5 now, “Air Filter Cleaner Housing Dump Valve NRC8955”.

If I hold my hand under the air filter, it blows air on to my hand. When I pull on the accel. on the fuel pump, it closes up. I just spoke to my mechanic, and he pointed out that if it was poor timing on the compression or exhaust stroke, the engine would be running terribly, which it isn't. He also mentioned the price of the duck bill.. apparently they're hard to find.

Might be time for a second opinion. Yeah I can’t find any duck bills domestically online anyway, BMI probably have them.

Well, for anyone following, after a bit of research it seems that some "reversion" due to exhaust and intake valve overlap can be expected at low rpm/idle. As for whether or not the amount I'm experiencing is normal, I'm unsure - service booked Monday so I shouold find out! After catastrophising about HG failure and bent valves, I'm leaning towards the valves needing adjustment and/or buggered lash caps (I'm sure we're all familiar with tdi lash cap issues) - the car is due for a 20k service, and with 330kn kms on the clock, it's not surprising that a tune up is in order. Cheers

That’s reassuring! My 300Tdi has 330k also, gets serviced every 5k but I need to book it in 3 months in advance to have a hope of getting around the date I want.