That horrid aluminium air pipe.

[Alec Dawe]

I've finally got round to removing the aluminium pipe from the exhaust to the bottom of the air filter box, as advised in a previous thread.
I was hunting for a funny resonance noise, which occurred only when changing UP at reasonable revs, just as the revs dropped for the next gear. Had sudden thought, 'wonder if its that bit of pipe'.
Removed nasty pipe, broken in two bits just by the support bracket off the chassis rail in the right side of the engine compartment. Removed all bits, stuck in dustbin, went for test drive.
I'm amazed at the transformation! Not only has the resonance gorn, but lots of other funny little noises that I had just put down to general old age have gone too.
Engine seems to run sweeter, rev better, and idles MUCH more smoothly!
All from removing a grotty bit of pipe.

[morsing]

Cool

If your engine actually runs better the chances are the valve in the air box is actually stuck on "hot". It should really be closed.

[Alec Dawe]

Originally Posted by morsing

Cool

If your engine actually runs better the chances are the valve in the air box is actually stuck on "hot". It should really be closed.

I'd wondered about that after I noticed how much better the engine ran, but no chance this evening to have a look in the air box!

[Velorum]

Any advice on how to check the valve in the airbox? My Haynes manual does not seem to shed much light on this.

Ian

[Clifford Pope]

Just point a hairdrier at it and watch the flap move.
If yours was stuck on open you did well to remove the pipe just in time.
Mine burnt out the air filter - it started smouldering! , and destroyed the Air Mass Meter.
Pull out the valve mechanism and put a WD40 cap or similar over the inlet .

[TOOLS]

Does this apply to carburetted models too. I fitted a replacement aluminium pipe to mine some time ago, as I thought drawing cold air into the carburettor during the winter months was bad for the engine. In summer it might be ok. Shurely Volvo must fit this system for a reason ?

[Clifford Pope]

I think the only reason for avoiding very cold air in winter is if the carburettor has a tendency to ice up. Otherwise, my understanding is that an engine runs more efficiently on cold.

Posters on Brickboard.com from Canada and Alaska report no adverse effects from removing the pipe.

I've never really understood its purpose anyway. There would be little or no hot air at the end of the pipe until the exhaust pipe had warmed up, so it clearly would be no use in easing starting. By the time the pipe was warm the engine would have been running some time and presumably the car well on its journey.
Old carburettor cars used to have a winter setting on the air cleaner, which moved the intake closer to the exhaust manifold. I can imagine that being more effective sooner after starting, so why interpose a 4 foot pipe?

Hi the horrid pipe you're discussing does it go from the manifold to the air box ?

If so it's a warm up pipe to give the engine warm air to help it idle easier it's now outdated technology. I know of one VW service manager who doesn't know what it is!! Shows how old technology it is.

9 times out of 10 the pipe (which if I'm on the same pipe) is a piece of soft aluminium the pipe is degraded to such a point that it's normally in at least two pieces like the one I pulled of my 760.

Removing it will have no detremental effect or not that you will notice.

Charlotte

[cbyard]

Presumably because engines are generally crossflow now, so the inlet and exhaust manifold are no longer on the same side of the engine. Or else the air filter is remote from the carburetter / throttle body anyway....

Chris

[Velorum]

Removed my pipe this evening - excellent result - less noise and better running! Will investigate whats going on with the flap in the air box at the weekend which I dont think will take too long.

Amazing how a small job that takes less than a minute can cause such an improvement!

Ian