Car Talk: Why does this '51 Chevy release smoke going downhill?
Dear Car Talk: I have a 1951 Chevy, straight-6, 3-on-the-tree, with 31,000 actual miles. Nice car.
If I coast downhill in gear (it doesn't happen in neutral or if the clutch is disengaged), when accelerating after the downhill run, it will briefly (for perhaps 100 feet or so), put out a puff of smoke.
What gives? — John
That's the worst problem you have with a car that's old enough to collect Social Security? You should be dancing a jig instead of writing to us, John.
On a car of this generation, blowing some blueish smoke after coasting downhill is not unusual. As a matter of fact, even some newer cars do it, but to such a small degree that it's barely noticeable.
Your problem is that your piston rings are wearing out. The piston rings are supposed to fit tightly against the cylinder walls and scrape off all the oil before combustion takes place, so gasoline and air get combusted and your oil doesn't. Your piston rings aren't doing a great job anymore. Not that they were stellar to begin with.
There's a measure of industrial precision called "tolerance." Tolerance is the space between parts. Back in 1951, manufacturing tolerances just weren't that good. You could slip a hot air balloon between some of the parts in this car.
These days, our manufacturing processes are infinitely better, and tolerances are much smaller, resulting in better performance and much longer engine life. But back when your car was built, nobody expected you to go more than 75,000 miles without an engine rebuild.
You're seeing that smoke because when you coast down a hill, the wheels are turning the engine rather than the engine turning the wheels. During that time, while there's little combustion taking place, oil is getting pumped past those poorly made and worn-out rings, and it is pooling in the cylinders. Then, once you start to accelerate again, that oil is getting burned up along with the gasoline and sent out the tailpipe.
Unless it's really driving you nuts, John, I'd just keep the oil clean and topped up and live with it for now. After all, given your annual mileage (we calculate 455 miles a year), you're going to be due for an engine rebuild in the year 2115 anyway.
Dear Car Talk: We have a 2013 Avalanche with automatic steps going in and out. The step on the passenger side sometimes stays in when we open the door, whether getting in or out. Getting out, if I'm not watching, I could fall out, being a small person. The warranty outfit will not fix it because when the guy looked at it, the step did come out, so he claims it worked for him.
Any way you can help with letting me know what could be the cause, and how to fix it? —JoAnn
You're talking about the motorized running boards, JoAnn.
As you say, it pops out between the door sill and the ground when you open a door, making it possible for non-NBA players to get in and out of vehicles like the Avalanche. And when they fail, it's either the switch or the step's motor.
When you open the door, there's a switch on the door jamb that signals a computer to turn on the dome lights, among other things. On some cars, opening the door turns on exterior lights, fires up some parts of the dashboard, unfolds the side mirrors or moves your seat back to allow easier access. In your case, it's also supposed to switch on the running board's electric motor, so it deploys for you and keeps you from having to fetch your 6-foot step ladder.
It could be the switch. More likely, though, the motor that moves the running board in and out is failing. Electric motors often fail intermittently. And that's going to be pricey to replace.
You definitely want to push harder to get this fixed under what I assume is your extended warranty. The guy you saw is hoping you get discouraged and go away. Don't. Reporting it to him was a good start. Make sure you save that repair order.
Next, start using your smartphone to take a little video every time you get in and out of the truck. Point the camera at the bottom of the door and start recording. Then open the door and film the running board.
If the running board operates normally, delete the video. If it fails to deploy, and you capture it on video failing, take that evidence to the repair shop and insist that they fix it. If you have several videos from several different days, all the better.
If they still give you the runaround, send that same video evidence, along with the repair orders, to the warranty company, and ask them to either fix the running board or refund the money you spent for a useless warranty. Good luck, JoAnn. And watch your step.
Got a question about cars? Write to Ray in care of King Features, 628 Virginia Drive, Orlando, FL 32803, or email by visiting the Car Talk website at www.cartalk.com.