TOM: Well, you might want to stop wearing those flowered sundresses on New Year’s Eve, Brian. That’ll go a long way toward winning him over.
RAY: I’m wondering if it could be the manifold gasket that blew, rather than the manifold itself? I’ve never seen a manifold actually blow off an engine (although I’d like to!), but I can give you a semi-intelligent explanation for a blown manifold gasket — which is a rubberized “seal” that goes between the manifold and the engine.
TOM: If the manifold gasket was already cracked or breached somehow, that would have allowed extra air to be sucked into one or more of the cylinders, creating what we call a “lean condition” — that is, too much air, not enough gas.
RAY: My brother usually has too much gas, but that’s a discussion for another day.
TOM: A lean condition also can be caused by a faulty fuel injector or a misfiring coil. But whatever the cause, a lean condition can lead to a backfire, which is an explosion in a cylinder that happens when it’s not supposed to — when the valves are open instead of closed.
RAY: And a backfire can go in one of two directions: It can either go through an open exhaust valve and come out the tailpipe, or it can go through an open intake valve and come out the air intake — which is what happened on your car, Brian.
TOM: The backfire is most often recognized by the loud “ka-boom” it makes, and, occasionally, by the pieces of your former manifold or exhaust system clanging down the road behind you.
RAY: My guess is that a backfire blew out what was left of your already-compromised manifold gasket. That’s what made the car run rough.
TOM: If it really was the manifold itself that blew off, it would have to have been a heck of a backfire — like the ones they use in the “William Tell Overture.” Or the manifold would have to have been cracked or loose before the backfire occurred.
RAY: In either case, now that you’ve replaced the gasket and resecured the manifold, you’ve probably also solved the backfire problem. So my guess is that you’re good to go, Brian.
TOM: But if the car backfires again, you can impress your father-in-law by asking him what else — other than a crack in the intake manifold or manifold gasket — can cause a lean condition in an ’01 Sable Wagon. Then just nod your head as he goes through the list and say, “Yeah, that’s what I was thinking, too.”
Sounds like this guy didn’t know what he was doing
Dear Tom and Ray:
We had a dead battery and called for a jump-start. The service agent could not jump-start the battery with his cables. He then proceeded to turn another battery over and lay it on top of my battery. Is this a common practice, and is this a safe practice? Could this have caused any damage to the electrical system? He left all the accessories on, and my headlights blew out and the alternator had to be replaced. — Susan
TOM: Can it cause damage? Apparently, yes!
RAY: It shouldn’t, if it’s done correctly (leaving out, for a moment, the issue of spilled battery acid). When you jump-start a car, essentially you’re touching the terminals of two batteries together. You’re just doing it via cables. So if you remove the cables, it should work exactly the same way, electrically speaking.
TOM: Unless you touch the wrong terminals together.
RAY: Bingo.
TOM: And that’s what this guy did. He hooked up the batteries backward. They were in series — like when you line up several batteries inside the tube of a flashlight. So instead of 12 volts, he sent 24 volts through your electrical system.
RAY: Some accessories can handle that. For instance, if your windshield wipers had been on, the motor would just have pushed them to wipe so fast that the raindrops wouldn’t have known what hit them.
TOM: Any accessories that were turned off would be protected, as would any components that are protected by fuses or fusible links.
RAY: But some things just can’t handle 24 volts. Your headlights, for example, probably blew immediately. And if you’d had other lights on, like the taillights, they probably would’ve blown, too. Or at least suffered some damage that would’ve shortened their lives.
TOM: And the alternator can’t take 24 volts because the diode bridge gets burned out.
RAY: But there won’t be any hidden damage. Anything that was harmed will be apparent to you because it doesn’t work now, or is on fire.
TOM: But you might just notice that everyone on your car radio is now talking twice as fast.
Send your comments or questions for Tom and Ray to: Car Talk Plaza, P.O. Box 3500 Harvard Square, Cambridge, MA 02238. Visit them online at www.cartalk.com.
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