Puff the Magic 9-3
September 8, 2006 8:15 AM   Subscribe

An occasional-to-frequent puff of smoke when starting up a Saab 9-3, and the engine seems to threaten to stall out...

When I start up my 2001 Saab 9-3, the ignition turns over and the engine starts, but the engine sounds like it might cut out. This "fake stall" might happen once or twice.

When this "fake stall" happens, the engine RPM drops, then goes back up to the normal idling RPM. At the same time as the RPM drop, a puff of thin white smoke comes out of the exhaust.

Once the car starts up, it runs fine. I drove it 400 miles last weekend, and apart from the puff and the start-up oddities, it seems happy once it is on the road. I've read of turbochargers causing smoke, but the turbo functionality seems okay, as well.

I use my car infrequently, perhaps once a week, and the mileage is 53K, but I have been changing the oil every 5k miles.

I had to have a new Direct Injection Cassette installed at 45K. When that part failed, I stalled out in the middle of a busy intersection, so I'd like to know what might be causing this latest problem before taking it to a repair shop and spending thousands of dollars.
posted by Blazecock Pileon to Travel & Transportation (11 answers total) 1 user marked this as a favorite
Best answer: Black smoke bad, white smoke worse. Usually when you see white smoke it means you're burning coolant, which you should never do. For coolant to get into the combustion system you've got to have a crack. For oil - black smoke - to get into the combustion you can just have normal (if undesirable) wear an tear in the pistons such that some can slip by.

A crack & coolant would be consistent with an issue starting but less so running. Once the engine heats up sufficiently it can burn that coolant more readily than at startup, particularly if you've got a larger quantity at startup from it sitting and slowly dribbling.

The bad news is that fixing it will probably be expensive, maybe prohibitively so. The 'good' news is that chances are it's going to be just as expensive to fix it next week as it will be in a year, meaning you can likely live with it as long as you can stand it before you put the money into it.

I'd suggest you take it to a mechanic and describe the problem but don't elaborate on possible underlying issues. You'll have to leave it with them so they can start it up cold the next day but if you use it so infrequently maybe it's not an issue. When/if they come back to you and say it's a cracked block you can ask them how much worse it's likely to get and if it will damage anything else when it does so.

I expect they'll tell you that it makes no difference except that it might leave you stranded on the side of the road, but I could be wrong.

If you keep driving it, make sure you check the coolant levels periodically. If it doesn't lose much then simply dumping some water into the overflow container from the radiator periodically will likely be sufficient, though initially you should remove the radiator cap when the engine's cool and look to make sure it's topped off.
posted by phearlez at 8:45 AM on September 8, 2006

Response by poster: If the engine is burning coolant, how fast should I expect that the thermometer reading should be rising over time? So far the reading has been consistent, for as long as I can remember.
posted by Blazecock Pileon at 9:16 AM on September 8, 2006

Best answer: White smoke isn't always coolant. Smell the smoke; does it smell oily, or does it smell sweet?

All sorts of things can cause the RPM drop that you cite. Could be something as simple as a vacuum leak.
posted by Kwantsar at 9:30 AM on September 8, 2006

Best answer: If the source of your problem is coolant leaking into a combustion chamber, you'll probably also soon notice discoloration of the coolant, too. And, your car will be more likely to overheat, not only because of loss of coolant into the combustion chamber, but because of hot combustion gases getting into the coolant, and driving up the pressure and temperature of the coolant, as well as dumping combustion by products into the cooling system.

A coolant leak can be caused by cracked heads, cracked engine block, or just a head gasket gone bad. Often a cylinder compression test can pinpoint a cylinder with low relative compression as the culprit where the leak is occurring. The rate at which the problem will worsen will depend on the physical size of the defect causing the leak, how often your engine goes through a warm up/cool down cycle, and how hard you drive it. For a pinhole leak in a head gasket, driven slightly and lightly, you could go a few months. On the other hand, the higher pressures and temperatures caused by combustion gases leaking into your cooling system could blow radiator hoses, or cause pinhole leaks in your radiator, or water pump gaskets prematurely, too, which could add to the expense of repair when you do get it fixed. Basically, if you have a coolant leak, you have an unreliable vehicle, that can fail and leave you stranded in several ways it normally wouldn't, and such failures are less predictable the longer you drive it.

You can also do a tail pipe "paper" test that might be instructive, if you have a friend to start the car, or can rig a paper bag with a big hole in it over your tail pipe when you are starting up cold. The basic idea is to trap any fine water droplets making it through the tailpipe in your "white smoke", to a piece of paper or a plastic bag on the tailpipe, where their tell tail sweet odor demonstrates they are coolant. I've seen a few cars with bad automatic transmission shift modulators puff smoke when they pulled automatic transmission fluid into the vacuum system, but this isn't usually the definitive white smoke on start up of a coolant leak. If you're getting a good puff of white smoke, the paper test will often trap sufficient spots of liquid coolant getting blown through your exhaust to make the diagnosis definitive by its sweetish odor and taste (coolant is poisonous to people and animals, so don't taste it much. And, coolant is also pretty bad for your catalytic converter).
posted by paulsc at 9:52 AM on September 8, 2006

Best answer: Bluish white smoke at startup can be a sign of worn valve guides. The valve guides ordinarily provide a seal against oil leak-down from the heads into the combustion chamber. One week between starts allows plenty of time for oil to sneak past the valves, then at startup the oil burns out of the cylinder, possibly throwing the O2 sensor off enough for the computer to make the engine stumble. Worn valve guides are not an emergency but you might want them replaced eventually.
posted by 55TaskForce at 10:08 AM on September 8, 2006

Best answer: Saabnet is your friend for all questions Saab related.
posted by Floydd at 10:42 AM on September 8, 2006

Best answer: Also, if the oil looks like a chocolate milkshake (rather than normal golden-to-brown clear oil), that's indicative of coolant entering the combustion chamber.
posted by fet at 12:42 PM on September 8, 2006

Best answer: fet writes "if the oil looks like a chocolate milkshake (rather than normal golden-to-brown clear oil), that's indicative of coolant entering the combustion chamber."

And you shouldn't run the engine until it's fixed, oil/coolant mixture has the lubricating properties of grinding compound.
posted by Mitheral at 2:07 PM on September 8, 2006

Best answer: fet is right, but I'm not the only person in the world who has needlessly panicked upon seeing a chocolate milkshake in a cold crankcase because he couldn't differentiate between a blown headgasket and harmless condensation.
posted by Kwantsar at 8:32 PM on September 8, 2006

Response by poster: Also, if the oil looks like a chocolate milkshake (rather than normal golden-to-brown clear oil), that's indicative of coolant entering the combustion chamber

I last changed the oil around 49K or so. The oil was dark black (as it usually is on a change) but not chocolate-shakey. I suppose I could check the dipstick to be sure?
posted by Blazecock Pileon at 10:27 AM on September 9, 2006

Meh. In cars I've owned, checking the oil filler cap worked just fine, because the camshaft(s) were throwing oil all over it during operation.

Also, if you want to rule an oil-and-water-going-where-they-don't-belong problem out without a visit to a shop, I suggest guys like these. You can probably get a kit from your local auto-parts store. My guess is that Autozone or Pep Boys will stock these kits; you prepay for the test when you buy the sample bottle.
posted by Kwantsar at 10:27 AM on September 10, 2006

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