Heat Exchangers leaking air

Oracle · 11-29-2003, 02:57 PM

Hi,
After I fixed the hose connecting the flapper box to the Heat Exchanger I could finally feel the breeze of air...

But when I was double-checking the work underneath the car while the Engine Blower motor was on I found that both heat exchangers have a very good air leak.

Is that normal?

I can see some rust on the surface but nothing like a hole just a little area a bit rusted off...

In the picture I have pointed where I can feel the air coming out in one of the heat exchangers (the other one looks similar)

Any comments?

Thanks
-J

Jim Sims · 11-29-2003, 03:16 PM

The gap between the shroud and the header pipes which you point out in your attached image is more or less a normal condition in most heat exchangers (heater boxes) I have seen. In the SSIs' I've seen, this gap is smaller but it is still there. If this gap was closed by welding I would expect to see cracks and sheet metal buckling due to excessive thermal expansion stress in the shroud as the header pipes will typically heat up more than the sheet metal shroud. The unfortunate side effect of this design is that if there is oil dripping onto the heater boxes and hot header pipes it will burn and smoke. Then the smoke will sometimes be drawn into the heater box air and then into the cabin; this can especially happen while idling when the air flow through the heater boxes is reduced. Cheers, Jim

Oracle · 11-29-2003, 08:53 PM

Hi Jim,
I understand the gap is there for a reason but it's Ok to feel air coming out of that?
That means that a very good amount of warm air is lost that way....
Since I've never seen a heat exchanger I kind of have to imagine the internals of it and in my mind (mental design

) there should be no air leaks at all...

As long as everything is still Ok and I don't have to buy new Heat Exchangers I'm happy... (I do have to buy one flapper box thou)

Thanks
-J

Jim Sims · 10:59 AM

These air leaks don't matter too much. Some heated air is lost in the winter but it is all a matter of economics. Welded in bellows spanning the joints or packed type seals (high temperature packing would be required) could be used to make these joints air tight but they would make the heat exchanger significantly more expensive to manufacture and in the case of the packing harder to maintain. It's much easier to design for leakage while still having enough air going forward to warm the cabin. The air cooled 911's were/are a little deficient in these areas in the colder climates - hence the optional gas heaters offered in the early years and the heating booster fans in later years. Cheers, Jim

Oracle · 11-30-2003, 07:23 AM

Thanks so much Jim for your comments.
I'm really happy everything is fine...

Bye
-J

Todd Simpson · 11-30-2003, 07:27 AM

Quote:

The unfortunate side effect of this design is that if there is oil dripping onto the heater boxes and hot header pipes it will burn and smoke. Then the smoke will sometimes be drawn into the heater box air and then into the cabin; this can especially happen while idling when the air flow through the heater boxes is reduced. Cheers, Jim

You just answered a question I've had for 5 years, how and why smoke would get in my defroster vents. Thanks!