My 123 diesel has a hole in the air filter housing where it's been banging against the valve cover. Not a huge problem, but I guess this means it's sucking in warmer air from the engine compartment. Could that cause any trouble or performance loss? I have some leftover aluminum sheeting (from making an EGR blocking plate - only installed while I take my station wagon off-roading, of course) that I could fit to cover the hole if anyone knows a good way to fasten it to the housing.

I've also got this strange rubber hose that comes out of the firewall (almost in the middle but slightly towards the passenger side, by the battery). It is fairly large (1.5 inch diameter?) and connects to nothing; it has a funny sort of diamond-shaped opening, which seems to me like it's supposed to let air out but not in. Is it a vent of some kind for the cabin? It has dried out and has some major cracks and holes in it. Probably not a big problem (assuming it's a vent) but is it replaceable?

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'81 300TD Wagon 355k (Miss Diesel)
'83 300SD 180k
'84 500SEL 190k (Parting it out)

I would stick some duct tape over your air filter housing if you're worried about it. I think the hose you're talking about is probably a drain (for water). I would check Fastlane first to see if ir's listed if you're going to replace it.

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1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k

As for the hole in the air cleaner, as long as the air isn't bypassing the filter, no problem.

And as far as the hose on the firewall, there should be two, they're the drain hoses for the A/C, if you pour water in the vents below the windshield it comes out of those holes, if they're too deteriorated you will get hot smelly air from the engine compartment sucked into the A/C

here's the pic from fastlane, though they aren't available right now, and the one in your car is probably black

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83 240D four bagger stick diesel 276K

No, it isn't bypassing the air filter... I would definitely have plugged it already if so .

Two? I guess there's one on the other side that I haven't seen. I haven't noticed any hot smelly air coming in, but then again my AC doesn't work . I might as well replace them though, if I can find some somewhere. The AC will be fixed some day...

Thanks guys!

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'81 300TD Wagon 355k (Miss Diesel)
'83 300SD 180k
'84 500SEL 190k (Parting it out)