Airbox that blows?

[MikeT]

While trying to trace the wiring that disappears behind the airbox I felt a current of air that had me puzzled. The engine was running, both fans were stationary and any externally moving parts (belts & pulley's) were on the other side of the engine bay

It appeared to be coming from under the air filter housing, where the primary inlet hose joins the airbox underneath and it was quite a substantial waft considering the engine was just idling.

I may be mistaken but I'm sure this air was blowing out from under the airbox, rather than being sucked in as I would expect. To test it was indeed coming from the underside join between airbox & primary hose , I removed the airbox and restarted the engine. Sure enough, no draft.

Although it's not a problem as far as I can tell, can anyone explain this? (no more air jokes from AndersDK please )

[AndersDK]

Can anyone explain this? (no more air jokes from AndersDK please )

Nope - I'll leave it there
Me too I'm puzzled. Must be a pretty simple explanation on this though.

[CitroJim]

I've been puzzling this all evening

A 1.9TD really sucks. Yes, it really does, hard. NEVER place the palm of your hand across the air intake upwind on the air filter. It will hurt a lot. I did that once It blows too. On petrol engines I put the palm of my hand across the tailpipe to check for exhaust system leaks. That is OK but if you value having a hand attached to an arm don't do it on a diesel

Against that background, it is quite possible that the amount of suck going on around a joint that does not seal particularly well (the braided pipe that comes in below the airbox) can cause a draft from air being drawn IN to the airbox that can indeed feel for all the world like a draft blowing out.

Also, in that region you are in very close proximity to the intercooler and its pipes and both these can most certainly blow a fair draft out if there is any leaks at all in either the pipework or the intercooler.

Given all your other power issues Mike, I'd be very tempted to seriously investigate around there again for leaks. Moving the airbox around looking for the cause of the draft may have inadvertantly moved something on the intercooler pipes and temporarily stopped the leak.

[Peter.N.]

There must be something available that will produce smoke or fog or something, that can be directed into the airstream so that you can actually see where its going/coming from.

[MikeT]

Me too I'm puzzled. Must be a pretty simple explanation on this though.

It's surely me, I'm the "simple" explanation.

Maybe I saw the stationary stays of the fan covers? But the draft was localised to about 2 square inches and I felt nothing else across the back of the rad and I couldn't hear the fans running. I was fighting hard not to be distracted from the job in hand (investigating my coolant temp warning) so I'm probably mistaken.

[MikeT]

A 1.9TD really sucks. Yes, it really does, hard. NEVER place the palm....

Too late and I've got big palms

Against that background, it is quite possible that the amount of suck going on around a joint that does not seal particularly well (the braided pipe that comes in below the airbox) can cause a draft from air being drawn IN to the airbox that can indeed feel for all the world like a draft blowing out

This is my only conclusion right now, I can test that theory.

Also, in that region you are in very close proximity to the intercooler and its pipes and both these can most certainly blow a fair draft out if there is any leaks at all in either the pipework or the intercooler.

I was distracted and concerned enough with that thought to remove the airbox and when I did, I couldn't find the draft. That's when I stupidly tested the bare intake - lucky I kept my fingers spread and reacted just before the intake pipes fully imploded - I've never seen my hand flex inwards that way before

Given all your other power issues Mike, I'd be very tempted to seriously investigate around there again for leaks. Moving the airbox around looking for the cause of the draft may have inadvertantly moved something on the intercooler pipes and temporarily stopped the leak.

Well power is improving as per No Black Smoke thread - loss of front grip is becoming the new bug bear but I shall investigate more when I can.

[MikeT]

If I push down on the airbox, the air leak is to all intent and purpose sealed. I'm 99.99% sure this pulsing of air is coming from the primary intake hose to the underside of the airbox join which is just a push fit and as said, does not seal well because it isn't critical.

The ambient breeze foiled my smoke test so I held a rizla in the turbulence and it just oscillated like a flag on a car I let the rizla go and it hovered, making me think Jim's theory was right, then it fell back into my hand, it moved towards the airbox, it moved away, it was like it was dancing

Eventually it did blow away from the airbox so I'm still inclined to think I'm right, that's it's blowing - how strange.

[AndersDK]

If it is from the "raw" air intake (non filtered) then commonly there are a series of holes - on purpose - to prevent standing waves (and hence more noise) in the air inlet.
Its purely an anti-resonance issue.

These holes are found also on the earlier BX paper air intake hoses - for the same purpose.
You can clearly feel there is a distinct pop of air pressure from these holes while engine is running - completely normal then.

That said - it still seems you have a misaligned seal on your airfilter box.