Dear Tom and Ray:
I am a Peace Corps volunteer in eastern Madagascar, and somehow I've been able to download you guys in my small bamboo hut in the middle of the rainforest. You two would love the way they keep these ancient old Fords running! But here's my question: How safe is it to jack up and change a tire while keeping the vehicle running and all passengers on board?
Tom: Well, we apologize that the Internet has made us virtually inescapable anywhere on the planet. You have our condolences.
Ray: I'm guessing that the reason you'd want to keep passengers in the car with the engine running while changing a tire is for their comfort and/or safety, right?
Tom: Since it's a rainforest, they stay dry in the car, and possibly air-conditioned, too. And inside the car, there are no ring-tailed lemurs swinging down out of the trees to steal their Papa Gino's.
Ray: In any case, the primary danger during a tire change is that the vehicle will slip off the jack and injure the tire changer. So the most important thing you can do before changing a tire is secure the car and make sure it doesn't move. Anything that increases the chances of the car moving should be avoided.
Tom: So if the vehicle has an automatic transmission, there's no reason you can't leave it running while you change the tire. You'd put it in park, apply the parking brake and chock the wheels (you'd wedge a large rock or a piece of wood in front of a front tire and behind a rear tire) to secure the vehicle.
Ray: If, on the other hand, the vehicle has a manual transmission, running the engine eliminates your ability to park it in gear. So all you've got is the parking brake and the wheel chocks.
Tom: So if it's a manual transmission, here's what I'd do: You can leave the engine running while the tire changer prepares the spare tire and gets the jack in place. You can even leave it running while he breaks loose the lug nuts and gets them started.
Ray: But once he's ready to jack the car off the ground, then you should turn off the ignition, put the transmission in first gear or reverse, and inconvenience your passengers for a few minutes while the wheel is actually removed and replaced. They'll survive. Once the car is back down on the ground, then you can take it out of gear and start the engine again.
Tom: And needless to say, whether the engine is running or not, you want your passengers to sit relatively still. You don't want them rocking back and forth to a rousing rendition of "99 Bottles of Beer on the Wall" while the car is off the ground. Good luck, Kelly!
(Car Talk is a nationally syndicated column by automotive experts (and brothers) Tom and Ray Magliozzi. Write to them at the Car Talk website.)