Drive it forever
Q. I have a 1991 Jeep Cherokee with 228,000 miles. It is equipped with a 4-liter straight six.
It ran hot, so I pulled over to cool it down and filled the coolant. Now, when it's standing still, it will run hot. I put in a new radiator, thermostat, and electric fan - now it has two. It will get about 240 degrees at standing still, but not into the red zone. There is no oil in the water. It has not lost any power, it doesn't leak oil or water, and I've never had to add oil between oil changes. What's causing this problem?
A. Replace the water pump. Sounds like the pump impeller is corroded away.
Q. I recently changed the spark plugs and wires in my 1998 Mazda B4000 pickup, and now it wants to spit and sputter. I checked the gap twice before installing them. What could be causing the sputtering?
A. Dollars to doughnuts, you've crossed two of the spark-plug wires.
Q. I recently wrote to you about a problem I was having with my engine after changing the spark-plug wires.
You were right. I did have two wires crossed, but now I've found that the catalytic converter was plugged up as well. And I don't understand what one has to do with the other.
A. I'll bet another dozen doughnuts that the misfire from the crossed plug wires made the catalytic converter fail.
A misfiring cylinder dumps its entire charge of unburned fuel/air mixture into the exhaust. The converter burns this off, which is what it is supposed to do, but it's not designed to burn the entire amount of fuel from a misfiring cylinder.
The heat generated by the extra fuel can turn the converter's precious-metal catalyst into molten slag in less than a minute. You'll need to replace the converter.
Q. We have a 2006 Chevrolet 5500 Kodiak diesel bus that has thrown a serpentine belt after only 15,000 miles. The dealer says that this is normal for these units, and to replace it every 10,000 miles or so.
I noticed that all the pulleys are six-groove except the A/C pulley, which is an eight-groove. The belt is a six-groove. The dealer tells me that's just the way they are.
Is it reasonable to replace the A.C. clutch pulley? Or do we just live with it?
A. I can't say if 15,000 miles is normal, but what did the old belt look like? Was it merely thrown, or was it actually worn out?
A six-groove belt should be fine riding on an eight-groove pulley, which I'm sure was done solely because the A.C. compressor already came from the supplier with an eight-groove pulley.
I'd take a close look at the alignment of the pulleys. It's critical that they all be in the same plane, and also that all be pointed in exactly the same direction as the crankshaft. There might be a misalignment, which could have caused premature wear or have thrown the belt off.
Needless to say, it's also important that the belt tension be checked regularly.
Q. I have a 1996 Nissan pickup. The ABS lights in the dash came on, and now I have very little brake pressure.
I've looked over the brake lines and the fittings, and see no leaks. I've also added fluid to the almost-empty reservoir, and still no pressure. Is there a solution to this problem?
A. You let the level of brake fluid in the reservoir get far too low. When you applied the brakes hard enough, the master cylinder sucked in an air bubble when you released the brake pedal.
You've refilled the reservoir, but the air is still in there.
You'll need to bleed the brakes to remove the air, and I'd flush the system at the same time.
Mike Allen is a senior editor for Popular Mechanics magazine. Questions should be sent via e-mail to driveit@nytimes.com.
