Richard Kent

Decided to drive my 95 993 today after being garaged for 6 months and noticed a bit of oil spotting on the garage floor. Turning up the heat bluish/exhaust smelling smoke started pouring out of the vents. Turning off the heat stopped it?
I only had a chance to drive 20 minutes to work and still blue smoke coming out of the vents if I turn the heat on. Just oil on the heat exchangers? or a hose loose?

FisterD

Since you have spotting on your floor, I would suspect it is just oil that has dripped on your heat exchangers and is now burning off. It wouldn't hurt to jack up the rear end and give it a good visual inspection.

jscott82

Oil on the outside of the heat exchangers may not be a concern... but anything getting on the inside (and blowing out the vents) would be a concern. The only thing between you and carbon monoxide poisoning is the exchanger walls. If there is a defect there, that needs to be taken seriously.

All that being said, it could be as simple as the little rubber flaps in the vents under the car have deteriorated and are not sealing.... still needs to be looked into though.

edit: To be clear, I think Darin is exactly right on the oil leak... but in a properly functioning system the oil smoke should not be making its way into the passenger compartment under any circumstances.

chet

When I had smoke coming out my vents a year ago it was because my left side motor mount had leaked fluid onto the engine tin in the corner. The air intake for the heater system connects to the top of the tin and the heater tube carrying the air down into the insides of the heat exchanger connects to the underside of the tin. Some of the fluid puddled in that corner seaped into that connection.

IXLR8

The oil dripping onto the heat exchangers eventually makes it into them if the car is parked long enough with leaking valve cover gaskets or if oil spewed out of the oil filler while adding oil and ran down onto the heat exchanger.

I have my heat exchangers off at the moment and noticed a lot of oil and grime at the inside bottom of each of them. I used a water based degreaser to clean them...they're like new again.

berni29

Hi There

I have had this very thing before. It is disconcerting to see smoke coming out of the vents in this manner. I thought the car was on fire.

I have had the whole rear heating system off the car including the exchangers. In my opinion the room for oil to actually get into the exchanger and burn off from there is limited. However there is plenty of tubing to perish and split and fumes can enter through these.

The answer is to fix the oil leaks really and replace any perished tubing. I would inspect the tubing (all of it!) very carefully. If no splits then I would find where the oil is dripping on to the exchanger (valve or timing chain cover perhaps?) and make up a shield out of folded tin foil and place/wedge it in so that it catches the drips and funnels it so that it exits away from the exchanger.

See if that makes a difference. Split pipes will let fumes into the car in my experience as well.

It is possible to fix. My heating works great now with no fumes or smoke.

Berni

Bob Rouleau

Oil on the heat exchangers causes smoke from the vents. Can also be caused by over filling the oil. Ask me how I know
White smoke out the vents on a race track is very disconcerting!

autobonrun

I bet it's oil in the exchangers from dripping on the outside. After sitting 6 months, quite a bit probably leaked on them. Use a mirror to check on top and see if you don't see oil on them. It can definitely find it's way inside. I had the same problem on my 79SC. Smoke would billow from the vents. It would be worse on turns, hard acceleration and braking. If you don't have major leaks, you should be able to drive if for a while and burn it all off. It will take much longer than 20 minutes however if there's anything significant inside. Find a nice curvy road with some long straights in between and get it up to temperature for a few hours. Just let your windows down. Cops will think it's a scene from a Cheech and Chong movie.

In my case, after fixing the leaks, I had to have the inside of my exchangers flushed. No smoke now however.

race911

What IS the CO content of burning motor oil? Of all the POS Bugs/Busses/914s/(yes, even 911s) out there over the years I've never worked on nor ever heard of heater issues leading to CO poisoning. But I'm all ears for some hard data on the subject.

(And yes, I've gotten ill from spending way too much time with worn out 2.4S MFI engines hooked up to a gas analyzer trying to pass CA smog when they used to be subject to testing.............)

IXLR8

And its only possible if you have an exhaust pipe leak due to a broken weld or a cracked pipe within the heat exchanger jacket.

If anyone is worried, place a CO detector indicator next to a vent. They're available from safety supply stores.

race911

My question went beyond combustion exhaust CO issues, and to the level (if any) of CO contained in burnt engine oil. Totally different.

IXLR8

Ahhh, yes. In either case, enough to give you a headache.

Amfab

Please correct me on the air flow path if I am wrong, but doesn't the additional blower in the rear have a a pipe in the engine compartment that feeds the heat exchangers?

IXLR8

I'm new to these, but I believe so.

There is even some pot scrubber stainless steel mesh within the heat exchanger between the inlet and the outlet. I assume that it acts as a filter for larger debris.

Here is a pic of the RHS heat exchanger. Note the clean inner walls of the heat exchanger jacket...


Here is a pic of what looks like stainless steel pot scrubber mesh. It was coated with oil and grime before I degreased the whole assembly...

race911

But a headache from the wonderful aroma, or actual first stages of CO poisoning? Sniffing the pipes of an old MFI car will get you in trouble quick at about 4% unloaded idle emissions. Still wondering if burned oil is anywhere near similar.