Oil Smoke in defroster vents

thastings · 06-09-2004, 04:01 AM

I am having a problem with smoke from the oil drip from the lower valve cover on my '72 911T Targa coming out of the heater and defroster vents. It does not matter if I open or close the heater gates.???????????????????????????????
It appears that the smoke is also coming out of the pre-heat box for the MFI and being sucked in by the fan. This means that it is coming from INSIDE the heat exchanger box on the driver side??????
This is not new. I now remember that this was one of the reasons I stopped driving it 10 yrs ago. But, now I have back on the road. Rebuilt the MFI and it runs great. It looks even better, until I stop at a light and the smoke starts pouring out of the dash. It's hard to sit in a P-car when people are telling you that its on fire.
Do the heat vent gates over the rear axle block the air coming from the exchanger when the vents are open?
Any suggestions?
Terry Hastings

Rot 911 · 06-09-2004, 05:26 AM

Terry you need to get under your car and see if the flapper boxes (what you call the heat gates) open and close. If you can see the slots are open then all the heated air should dump out of them and no more oil smoke in the car. You may have a broken cable or rusted boxes. Replacing the valve cover gaskets is a very easy maintenace chore of about 1 hour even if you have never done it before.

na2ub · 06-09-2004, 05:46 AM

I hate to admit it, but I drove half the summer with one of my flapper boxes rusted halfway shut. Finally I got under there an broke it loose, and got some welcome relief of driving my non-ac car without the heat on.

wrx paul · 06-09-2004, 07:11 AM

try removing the pipes from the back of the heat exchangers that goto the flapper boxes. If that stops it your on your way to fixing it. If its not all rusted together too bad I would remove your heat exchangers and degrease them. While those are off you can get to the valve covers and try and clean the mating surfaces and add new gaskets.

thastings · 06-09-2004, 01:06 PM

It does it with and without the gates closed.

I'm puzzled because it seems like the smoke is coming from INSIDE the left exchanger. I have never looked at a heater gate assembly off the car, and having failed to fine a diagram of it in any of the many repair manuals, factory and aftermarket, was wondering if there is an internal flap that rotates with the external flaps that block the heater pipe to the front of the car. If not, it seems to me that the open flaps would only work while the car was moving. What stops the heat from continuing up the pipe.

Having just got the car back on the road after lots of work (and$$$), and the weather being great, I was hoping someone knew of a magic bullet to solve this problem.

Oh well I guess its back to the lift, in the old garage, if I can ever get the kids cars off it again. Its a lot more fun to do it on a rainy, winter day, while the wife is cleaning (as in to busy to help her).

Thanks for the comments
Terry

Rot 911 · 06-09-2004, 01:26 PM

Yes there is also an internal flap. Here is an exploded view of the flapper box:

wrx paul · 06-09-2004, 04:44 PM

see in the picture pipe 3. I was saying to remove it. That way no air from the heat exchanger will enter the car and will just vent to atmosphere. Then you can see if the issue stops. If it does then you need to remove that heat exchanger and clean it. You might also be able to do it on the car but if it can be removed you'll do a more throrough job.

RoninLB · 09:54 PM

i once brought my oily HE to a radiator shop for cleaning.. but if it's not to oil soaked maybe an hour drive at 3.5k rpm will toast it so it's good enough. dropping those HE can be real work.

thastings · 06-10-2004, 04:25 AM

Thanks Kurt, the diagram clears up a lot of my questions. I don't see the interior flap moving, so I guess its time to put it on the lift and pull them out. Hopefully I only need to clean them up.
Now, what to do about the oil?
Thanks
Terry Hastings