Send your comments or questions for Tom and Ray to: Car Talk Plaza, P.O. Box 3500 Harvard Square, Cambridge, MA 02238. Listen to them Saturdays at 10 a.m. on 91.3 FM or 88.5 FM. Visit them on the Internet at www.cartalk.com.
Dear Tom and Ray:
I drive a 2004 Hyundai Elantra that was bought used, and I don’t know the history of the vehicle. Last evening, I unavoidably ran over a fairly large armadillo. It was big enough, and the car sits low enough, that it evidently struck the front bumper, which I understand triggers the airbags during a front-end collision. The airbag did not deploy; however, the airbag light on the dash came on and remained on for the last five miles of the trip, making me very anxious. This morning when I started the engine, the airbag light on the dash came on for the usual six seconds to indicate that the system is functional, and then went off. But is it functional? What happened? — Ginger
RAY: Luckily, armadillos are not on the list of airbag-deploying mammals, Ginger.
TOM: I don’t know the specifics of the airbag system in your car, but I’m pretty sure there are two sensors in the bumper. And I suspect they’re “inertial switches.”
RAY: Unlike an old-style switch where the contacts get physically “pushed together,” an inertial switch detects a very quick change in acceleration. For instance, were you to hit a 1,500-pound polar bear, your car would go from 50 miles an hour to zero in an instant. The inertial switch would register that and deploy the appropriate airbags.
TOM: But running over a small mammal, as disturbing as that might be, did not cause you to decelerate enough to trigger an airbag deployment.
RAY: It DID, however, register as an “event” with the airbag computer. The computer basically said: “Whoa! You guys feel that?” And that’s what caused the light to go on. The light is a signal that the computer is no longer sure all is well with the airbag system.
TOM: But, the next morning, the computer ran a self-diagnostic check of the airbag system, like it does every time you start the car. That’s when it confirmed that everything was working — except for the armadillo — and turned off the light. If you had pulled over and restarted the car right after the incident, the computer would have run a self-diagnostic check then, and the airbag light would have gone off then, too.
RAY: So your airbag system is functioning normally. Still, it would be worth asking your regular mechanic to have a look at the front of your car. Aside from armadillo parts, it’s possible you did some mechanical damage in the front end that you don’t know about, and your computer won’t tell you that.
Striking oil this way is not so lucky
Dear Tom and Ray:
I have a 1991 Chevrolet S-10 with the four-cylinder mill. I bought it because I had to park my Ford F-350 Dually when diesel fuel went above $4 per gallon.
I have had the Chevy less than a year and have had very little trouble with it — until I struck oil! I noticed that I had to add oil frequently. I wasn’t seeing any smoke or leaks. Then one day, I took off the radiator cap and discovered: OIL. How does oil get into the cooling system without getting water in the oil? The truck has a five-speed manual transmission, so there is no transmission oil cooler. The oil definitely is coming from the engine.
What could be the source of the oil coming into the cooling system when no water is getting into the oil? Help! — Allen
TOM: Well, unless in a drunken stupor, you added a quart of oil to your radiator one night, you have a blown head gasket or a cracked head. Or worse.
RAY: The reason the oil is going only one way probably has to do with the location of the crack. If the crack is near the oil pump, the oil passing by that crack is under as much as 100 pounds of pressure. So it’s being pushed into the water jacket, where the coolant is pressurized only to about 15 psi.
TOM: Eventually, you’ll get so much oil in there that all that extra volume and pressure will blow a cooling hose, or even blow the radiator. So, unlike Jed Clampett’s backyard bubbler, this oil discovery doesn’t bode well for you, Allen.
RAY: Here’s what I’d suggest. If the truck is otherwise in good condition, have someone pull off the cylinder head. If you’re really lucky, you’ll find a bad head gasket, you’ll replace it and you’ll put the head back on. End of story.
TOM: If it’s not the head gasket, then your mechanic can examine the head for cracks. If your head is OK (which has never been true in my brother’s case), then you have to assume you have a cracked block, and you’ll need to find a used motor for this little gem.
RAY: But if the truck’s in good shape, and diesel fuel stays up near $5 a gallon, it may be worth it, Allen. We wish you luck!
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