Oil/exhaust smoke through vents in cabin. Easiest fix?

[david05111]

Have SSI heat exchangers (they're a few months old at best, and have less than 500 miles on them, so they're not rusted). I was told that my heater boxes were shut, but they obviously aren't and they're letting in some heat and fumes. Somehow, oil is burning somewhere and its being blown into the cabin to the point of concern when the windows are up. It still smells of it when they're down as well, but at least it's not as concerning.

I did a little reading on this and it seems the common answer is that somehow oil is leaking onto or into the heat exchangers and it's burning off, thus being blown by the heater blower into the cabin through the vents.

The shop I've had it most recently to recently repaired an oil leak coming from the o rings on the oil cooler on the back of the motor. I thought that that would clear up the issue, but it hasn't.

The case itself -- the bottom end -- does weep a bit, but since I haven't had a bottom end done on the car, I expect it to leak a little oil. I didn't think that would drip onto the heat exchangers though. I guess I could be wrong?

1) I'd like to identify where this is coming from. Is there any chance this could be from the bottom end, and that it's basically not something that can be fixed easily? Is it most likely something up top?

2) In the event that this can't be easily solved, I need a way to resolve the issue. I hear that one common thing to do is to disconnect the heater hose between the SSI and the heater boxes underneath, so that fumes aren't pouring in. I know that you can't block up the SSIs themselves, as they need airflow. Is there a good way to seal up the heater boxes themselves, since replacing them isn't a priority at the moment? I'd love to replace them, but even if I did, I'd have the same issue I'm having now (oil smoke in the cabin).


I have to think that this is really, really unhealthy and I'd like to get to the bottom of it. But I really don't have a good idea where to start, aside from hunting for an obvious leak.

[Alan L]

I had a friend who had a 911S and he would pull to a stop and smoke would waft up from under the rear guards/fenders. Basically it was an engine out to fix - which we did after I saw the amount of smoke.
Some underside pics might help. It must be identifiable to be that bad.
Alan

[tobluforu]

Cheap and easy things first........Get under the car and have someone work the heater lever to see what's up. Years ago, mine was caked with road grime and was stuck open.
Next, spray some engine degreaser on the underside of engine, make sure it's not super caustic, pressure wash it off. Get yourself a nice and bright led light, drive car, park and search out leak. Might be valve cover gaskets, easy, might not.

[emac911]

My 88 had this issue when I got it. The car had been sitting for a long time, and had SSI installed shortly before parking it. Leaking oil return tubes and valve cover gaskets over time, the oil had made its way into the heat exchangers.

I removed the heat exchangers, fixed the oil leaks and cleaned out the heat exchangers. I used several different methods. I scoped the inside of the heat exchangers to find where the oil was and used rags attached to a flex rod to soak it up. The end fix was adding soapy water into the heat exchngers with the flex hose removed and going for a few drives.

[mb911]

Well it’s not exhaust (carbon monoxide) it is more likely oil weeping from valve covers, leaking oil return tubes or worst case leaking cylinder bases and the. Weeping into the heat exchanger and then creating the smell/smoke. Gotta fix the leaks

[Mark Salvetti]

How long ago was the oil cooler leak fixed? This could be oil from that leak that got into the SSI’s. Even after the leak is gone, the oil inside the exchanger is going to take a while to burn off.

Take the hose off the back end and scope the exchangers to see how much oil is still in there. It may just be the right side.

Mark

[mikesarge]

What is your (case) breather setup? Stock?

I was briefly running a catch can with a filter open to atmosphere in my engine bay. It caused these symptoms as combustion gasses were being scooped up by the cooling fan and shoved into the cabin. I routed it into my intake and that fixed it. Check out your breather setup, maybe that’s part of your problem!

[david05111]

Originally Posted by Mark Salvetti

How long ago was the oil cooler leak fixed? This could be oil from that leak that got into the SSI’s. Even after the leak is gone, the oil inside the exchanger is going to take a while to burn off.

Take the hose off the back end and scope the exchangers to see how much oil is still in there. It may just be the right side.

Mark

So when they got access to that, they tell me that they figured out it was the O-rings associated with it, not the cooler itself. They replaced those, supposedly solving that issue.

I'm a complete novice on most of this still. How would oil get into the exchanger from such a failure? I thought they only had like 6 ports? Three from the exhaust manifold, heater air entry, heater air exit, and exhaust to muffler. How would oil typically get into a heat exchanger like that?

I do have a scope and access to a lift, so I can do that. By hose off the back end, you mean toward the rear of the car or the front?

[david05111]

Originally Posted by mikesarge

What is your (case) breather setup? Stock?

I was briefly running a catch can with a filter open to atmosphere in my engine bay. It caused these symptoms as combustion gasses were being scooped up by the cooling fan and shoved into the cabin. I routed it into my intake and that fixed it. Check out your breather setup, maybe that’s part of your problem!

I honestly haven't the slightest clue, and I'm not even sure what half this means at the moment unfortunately. Can you point me to an article or something on that so I have an amateur understanding of it?

[david05111]

I took some of these earlier this afternoon. The heat exchanger on the passenger side of the car looks pretty clean. The one on the left side of the car looks to have some oil on it. I'm not quite sure where it's coming from though. The nuts on the case right above it are wet, but the edges where the gasket would be are dry. Maybe oil is leaking through the bolts somehow and onto the top of the exchanger?

As you can see, the engine is dripping some oil toward the front of the car (reference cardboard box on garage floor). I was told that the case itself was always going to weep until a bottom end was done, so I've chalked that up as normal. I'll see about getting under there with a good de-greaser and cleaning it as best I could so we can isolate old from new. I could use a recommendation for that, if someone has one.

[mikesarge]

Let’s see a photo of the engine bay- the oil is likely being sucked in by your cooling fan and blown through the heater tubes that way.

[david05111]

Originally Posted by mikesarge

Let’s see a photo of the engine bay- the oil is likely being sucked in by your cooling fan and blown through the heater tubes that way.

[Alan L]

The engine area is cleaner than I was expecting. Fingers crossed for you.
Basically I would solvent/degrease clean as much of the stuff you can get to, or suspect. Then hose off and pay close attention to what goes on after that.
Good luck.
Alan

[pmax]

It is more likely something else other than the 3.0 case leaking.

Main seal perhaps or the so called "triangle of death", not sure how it got that name.

Your cylinders, the ones visible anyway, look pristine which is good.

[Mark Salvetti]

Originally Posted by david05111

So when they got access to that, they tell me that they figured out it was the O-rings associated with it, not the cooler itself. They replaced those, supposedly solving that issue.

I'm a complete novice on most of this still. How would oil get into the exchanger from such a failure? I thought they only had like 6 ports? Three from the exhaust manifold, heater air entry, heater air exit, and exhaust to muffler. How would oil typically get into a heat exchanger like that?

I do have a scope and access to a lift, so I can do that. By hose off the back end, you mean toward the rear of the car or the front?

The heater box portion of the heat exchanger is not sealed where the header pipes that connect to the engine poke out the top. That is a slip fit, and oil could travel down through that gap. Don't forget that the oil that is dripping straight down in your garage will likely get blown around at speed. Oil will also be hot and less viscous. I can easily see the oil leaking from the o-rings landing on the right side exchanger and working its way inside.

Hose I suggested removing is toward the back end, at the muffler. There is a 90-degree bend into the heat exchanger, but it should be much easier to get a scope in there from that end than from the front of the exchanger.

Mark

[david05111]

Had it out today for a little bit. Haven’t had the chance to clean the underside to go hunting yet. I had it sitting on the edge of my garage for about 30 mins, running for about 20 mins of it. Wanted to check timing, etc.

While sitting there during that period, it leaked some oil. A few spotty bits and something about the size of a 50 cent piece. Pics for scale. It’s obviously leaking a decent amount from somewhere.

[Jeff Higgins]

The bottom of that engine is about as clean as I've seen on anything short of a fresh rebuild. I do see some oil on the left heat exchanger that appears as though it may be coming from the oil return tube. Not the two tubes returning oil from the cam towers to the case, but the crossover line that feeds oil back to the tank. It's not uncommon for the fitting that screws into the case to leak. It's not all that hard to reseal, but you do need to remove the left heat exchanger to get to it.

As clean as this engine appears, it begs the question - just how much smoke are you actually getting in the cabin? These things are hard to quantify over the internet, for sure, but what might appear to be "a lot" of smoke to you may be insignificant to someone else. The drips you show in your last photo certainly appear to be rather insignificant for a car that has been driven around, warmed up, and left parked in the same spot for half an hour, twenty minutes of that while running.

Most folks would be tickled pink to see that small of a spot under the circumstances you describe. You will never completely eliminate the faint smell of oil in the cabin of these cars. Just the nature of the beast. I've seen many of these cars that will, over time, deposit two thin little stripes of oil residue at the base of the windshield where the defrost vents blow. Those guys just wipe it off and carry on.

Has the engine ever been rebuilt? How many miles are on it? How long have you had it? Do you just smell oil, or is it puffing like a diesel truck? Does it stop after it warms up and burns out whatever may have dripped after the last drive?

[david05111]

Originally Posted by Jeff Higgins

The bottom of that engine is about as clean as I've seen on anything short of a fresh rebuild. I do see some oil on the left heat exchanger that appears as though it may be coming from the oil return tube. Not the two tubes returning oil from the cam towers to the case, but the crossover line that feeds oil back to the tank. It's not uncommon for the fitting that screws into the case to leak. It's not all that hard to reseal, but you do need to remove the left heat exchanger to get to it.

As clean as this engine appears, it begs the question - just how much smoke are you actually getting in the cabin? These things are hard to quantify over the internet, for sure, but what might appear to be "a lot" of smoke to you may be insignificant to someone else. The drips you show in your last photo certainly appear to be rather insignificant for a car that has been driven around, warmed up, and left parked in the same spot for half an hour, twenty minutes of that while running.

Most folks would be tickled pink to see that small of a spot under the circumstances you describe. You will never completely eliminate the faint smell of oil in the cabin of these cars. Just the nature of the beast. I've seen many of these cars that will, over time, deposit two thin little stripes of oil residue at the base of the windshield where the defrost vents blow. Those guys just wipe it off and carry on.

Has the engine ever been rebuilt? How many miles are on it? How long have you had it? Do you just smell oil, or is it puffing like a diesel truck? Does it stop after it warms up and burns out whatever may have dripped after the last drive?

I admit, I don't know what is typical. I expected that a weeping case might drip a few drops every 12 hours or so, so when I see that much in 30 minutes, that seems like a lot to me.

Regarding the smoke in the cabin, I'm trying to think of a way to describe it. Imagine blowing out a candle and the smoke you see trailing away. But think about blowing that candle out every 30 seconds or so. That's the amount I'm getting. It's noticeable, and accumulates when the windows are up. With the windows down, you can still smell it and it irritates your lungs a little, but it blows out. Obviously its a mix of both when you're sitting with the windows down and idling at a light.

The engine underwent a top-end rebuild last year. I've been chasing problems afterward because the shop made a lot of mistakes along the way, though not with the critical parts as far as I can tell. Re-used gaskets, improper timing, not checking all fuel system parts, mixture wrong, etc. Multiple threads on here about it.

The shop didn't really touch the bottom end much. They didn't break the case open.

I inherited the car when my father passed away, but he bought it new in '80 so it's been a constant presence. It did sit in the garage unused and unloved for close to 30 years though, so a lot of stuff was worn out. They had to do the head studs as part of the top end as well. If the odometer is to be believed, it has around 60k miles on it. He drove it a lot in the first few years owning it, some in the late 80s and early 90s, and then just parked it. Never thought to ask him why, sadly.

As far as the smoke goes again, it's tough to say. It certainly doesn't puff like a diesel truck. It does have heat exchangers and an M&K exhaust, so it's fairly open. Unfortunately, that does create an issue sometimes, as the fumes seem to kinda sit around the back of the car at idle at lights, etc. and the fan does catch some of them and blow them into the car. It's hard, therefore, to quantify and bifurcate one thing from the other sometimes. Basically, whatever is getting sucked in by the fan back there is getting driven into the car to some extent.

The other night, I replaced the injectors while using a buddy's garage (he has lifts and better tools). I ran the car for a bit, with the rear toward the open door of one of the bays. I had the heater lines on the left side disconnected (the one from the fan to the heater fan and the one from the heater fan to the driver's side tin). In a few minutes (15 tops), the car had smoked up the entire garage to the point we opened all the bays to vent it. It was burning oil off the heat exchanger, the smoke was getting picked up by the fan, cycled around the engine bay and basically never dispersed elsewhere. While the exhaust itself was aimed out of the garage, it just kept recycling the oil smoke around and around and flooding the garage. Is it conceivable it was still burning stuff off from the leaks the shop apparently fixed a few days prior? Possibly. It didn't really clean up all that much though. I drove the car back to my house with the windows down when it was 45 out as a result.

I'm sure a lot of this might not be as big a deal if I could just close the heater boxes. At that point, all the oil smoke and exhaust would get caught in the fan, but not able to get into the car. But the damn heater boxes are apparently not closed all the way, and they're rusted to the point that I really don't want to mess with them. I'd like to have a pro replace them, but basically no one wants to touch them anywhere at this point.

[PeteKz]

My guess: Rocker shafts leaking, dripping down onto the heat exchangers and getting inside.

If you can see smoke inside the cabin, that's way too much. Even a strong smell is too much. A very light background smell is more or less typical. I don't get any smell out of my SSI's, but I have been diligent about stopping oil leaks.

[david05111]

Originally Posted by PeteKz

My guess: Rocker shafts leaking, dripping down onto the heat exchangers and getting inside.

If you can see smoke inside the cabin, that's way too much. Even a strong smell is too much. A very light background smell is more or less typical. I don't get any smell out of my SSI's, but I have been diligent about stopping oil leaks.

Assuming you’re right, how would I verify that? I assume the first thing would be to scope the heat exchangers and check for presence of oil.

If there’s an appreciable amount present, is there some easy way of identifying the issue as coming from the top end as opposed to the bottom? The work is still under warranty, and if the rockers are leaking, that’s on the shop to address. I certainly don’t want to get into the nightmare that sounds to deal with.