It's probably time to replace oxygen sensors

Q I have a question about oxygen sensors and when to replace them.

I have a 1998 Dodge Durango with 200,000 miles on it, and the oxygen sensors have never been replaced. I am not sure if there are one or two. I do not have a "check engine" light showing, and the mileage has not changed much since it was new. Should I change the sensors now, or wait for a code to be set?

A I didn't find a specific replacement interval for replacing the oxygen sensors in your vehicle, but many carmakers recommend replacing the front O₂ sensors in the 75,000-120,000 mile range. Regardless of the recommendation, there's little question that the performance of a pre-catalyst O₂ sensor is degraded after that many miles. As the sensor ages, its ability to read and communicate the percentage of oxygen in the exhaust compared with the percentage of oxygen in the atmosphere slows down, reducing the efficiency of the engine management system to fine-tune the fuel-air ratio.

With today's vehicles, fresh pre-catalyst O₂ sensors are the heart of a modern tuneup and can help restore performance and fuel mileage.

Q I have a problem with my 2003 Acura RL. I bought it as a lease return in 2006.

It has really bad hard-water spots on all of the glass. I have tried using a few things to get them off but with no results. Is there anything out there that can help me? It is so bad that at night it makes it really hard to get a good clear look out the back. In really bad cases like this could you use a really fine-grade sandpaper or steel wool on the windows without damaging them? I am lost for a solution, so can you help me out?

A Yikes! Put down the sandpaper and step away from the vehicle. Seriously -- do not use sandpaper, steel wool or any other abrasive that could scratch the glass.

And here's another one that really got my attention: Brasso metal polish. I was skeptical when first told this, but then tried it on the outside of the windshield on one of my old vehicles. The windshield had a buildup of residue from oil, road tar, dead bugs, water spots and all manner of debris. The Brasso thoroughly cleaned the glass but left a film of dried polish on the glass. An automotive glass cleaner and wadded-up old newspaper did a nice job of removing the Brasso residue and leaving the glass spotless.

Q I have a 2005 GMC Envoy SLT with the 4.2-liter, inline six-cylinder engine and 31,000 miles on it. In January, after several below-zero mornings, it developed a squeal upon starting. It only lasts a few seconds, then quits. Immediately after it quits squealing, the dash lights get brighter.

It doesn't do it every time, but it seems to be more frequent when it's below zero. The squeal sounds like someone is skinning a live cat and causes heads to turn in the parking lot. I've taken it back to the dealer, and so far they've changed the serpentine belt and tested the starter, alternator and all the bearings and pulleys. It's still not fixed. Is there anything you would recommend?

A No question: The serpentine belt on the front of the engine that drives all the accessories -- water pump, alternator, power steering pump and air conditioning compressor -- is slipping at start-up. The dealer has checked for most of the common causes, but it might be worth replacing the automatic belt tensioner. If the spring is a bit weak, it may not be able to keep the belt tight enough to prevent a momentary slip at start-up, when the drive loads on the belt are at their maximum.