Rear Roof Vents

[bcgreen]

On my car there are the roof vents and I am wondering if they allow external gas fumes to enter the vehicle, because I do get some exhaust fumes inside the cabin.

[Rot 911]

What year 911 do you have? Any modifications to the exhaust system? If you are smelling exhaust fumes, much more likely you have perforations in the heat exchangers on your exhaust.

[bcgreen]

Originally Posted by Rot 911

What year 911 do you have? Any modifications to the exhaust system? If you are smelling exhaust fumes, much more likely you have perforations in the heat exchangers on your exhaust.

1976
If I do have perforations, would not the exhaust note be louder?

[Craig_D]

Originally Posted by bcgreen

If I do have perforations, would not the exhaust note be louder?

The heat exchangers are metal shrouds over your exhaust manifolds (headers), so the exhaust wouldn't be louder, but you'll have a chance of getting engine bay fumes carried into your cabin.

[bcgreen]

Originally Posted by Craig_D

The heat exchangers are metal shrouds over your exhaust manifolds (headers), so the exhaust wouldn't be louder, but you'll have a chance of getting engine bay fumes carried into your cabin.

Are there any pics of the exchangers and how easy to replace?

[Steam Driver]

"Back in the Day" a good friend of mine had his '66 911 try to do him in with exhaust. (The car was his daily driver - tells you how old this story is!) It wasn't noisy or anything, and there were no (readily) visible perforations anywhere in the system. But one night he got serious CO symptoms.

Turned out there was a small linear crack in the TOP of the muffler, totally out of sight. Our diagnosis was the fan was sucking the fumes from there and pushing them right into the car. So you never know where the hole is going to be.

That was an interesting car; about the second or third sold in K.C. Original owner was a long-time Porsche driver who's last ride before the 911 was a Carrera 2 Cab. (Wonder where that is now?) I don't know what happened to the '66 either; my friend sold it in 1971 to buy a 240Z and we lost track of it.

[Craig_D]

Originally Posted by bcgreen

Are there any pics of the exchangers and how easy to replace?

I would do research here on the Pelican forums. You seem very new to ownership of your 911?? Have you said what year you have?

[bcgreen]

Originally Posted by Craig_D

I would do research here on the Pelican forums. You seem very new to ownership of your 911?? Have you said what year you have?

I understand they are difficult to remove and one has to be careful and not break any bolts. If I were to see some sort of perforations, would not using some sealant take care of the issue, for a while?

[Bill Verburg]

Originally Posted by bcgreen

Are there any pics of the exchangers and how easy to replace?

The heat exchanger covers are tack welded to the exhaust headers
these are '73 RS MFI versions which should also be on your car

Left side w/ heat stove for MFI


Right side


SSI used to make clones of the oe headers for these cars, you don't want any exhaust leaks which were common in the old days before stainless was used, CO poisoning is insidious. You always want the covers to rot out before the header tubes other wise CO can get in to the cabin. The first versions were all mild steel, then they went to SS tubes w/ mild steel covers, I'm not sure if the factory ever went to all SS on these as they switched to the totally different smog exhaust in '75

SSI clones of the oe heat exchanger/header system, these are for later cis cars, no heat stove


remove the heat exchange cocver and you find the header tubes

[KTL]

The roof vents are indeed open to the outside of the car. But that location doesn't pull in air, it lets air out of the car.

[bluesky]

+1 on what Kevin said.

That area of the car at the top of the rear window would be a low pressure area (venturi-like) when moving, thus pulling air out of the car. The vent works with the perforated headliner to allow air inside the car to be pulled through and exhausted out of the car.

[bcgreen]

Originally Posted by Bill Verburg

The heat exchanger covers are tack welded to the exhaust headers
these are '73 RS MFI versions which should also be on your car

Left side w/ heat stove for MFI


Right side


SSI used to make clones of the oe headers for these cars, you don't want any exhaust leaks which were common in the old days before stainless was used, CO poisoning is insidious. You always want the covers to rot out before the header tubes other wise CO can get in to the cabin. The first versions were all mild steel, then they went to SS tubes w/ mild steel covers, I'm not sure if the factory ever went to all SS on these as they switched to the totally different smog exhaust in '75

SSI clones of the oe heat exchanger/header system, these are for later cis cars, no heat stove


remove the heat exchange cocver and you find the header tubes

Thanks for the pics. So I don't really know if the heat exchangers are my problem but suspect it is. Even I don't see any problem externally, it could have a leak on top of the exchangers that I wouldn't be able to see.

[Bill Verburg]

It's possible to get oil odor through the cabin heat but it generally gets burnt off thru use, Back in the day it was common to carry CO detectors in the cabin, that seems to have gone by the boards but if there is any suspicion that exhaust gas( not just burnt oil odor) is present in the cabin it would be worth while to use a CO detector while driving just to check.

911 thru '89 had the cabins vented above the rear window(you can easily see the vents), there is some foam back there that is supposed to keep water out, starting w/ 964 that area is sealed and cabin air leaves through ports at the side behind the seats