A Here's my semi-professional, completely biased opinion. My opinion on rustproofing -- like my opinion on extended warranty and service contracts -- has evolved over the three decades I've been writing about cars. First, let's distinguish between rustproofing and undercoating -- they are two different concepts. Undercoating is a relatively thick rubberized material applied to the exposed underbody and chassis to primarily act as a sound deadener. This coating obviously has some anti-corrosion properties but does not protect vulnerable areas such as boxed sections and the bottom of the doors.
Rustproofing is a lighter spray-on material that is applied to seal and prevent moisture from reaching vulnerable areas such as inner fender lips, door bottoms, inside door skins, boxed frame sections, inside rocker panels, door jambs, lower insides of the front and rear fenders, the cowl, the underside of the hood and trunk lips. The spray can reach untouchable areas and the material remains pliable, allowing it to flex, stretch and self-heal small scratches. Rustproofing can be very effective when applied properly and maintained on a regular basis.
That said, the build quality, alloys and galvanized steel used in modern automobiles has reduced the need for additional rustproofing. In fact, several carmakers like Volkswagen and BMW rustproof their vehicles when built.
When would rustproofing make sense? I used to rustproof used vehicles to prolong their service life, and I would consider having a new vehicle rustproofed if it had to survive more than a decade in a rust-prone environment where salt is used to de-ice roads.
However, the absolute best rustproofing is frequent car washing that includes a thorough flushing of the underside of the chassis, wheel wells and the inside edges of doors, hood and trunk. As a metallurgical engineer once told me, "rust never sleeps. Ferrous metals simply prefer to exist in an oxidized state. You can't stop rust; you can only slow it down."
Q I have a '95 Olds Cutlass Supreme with 100,300 miles. Lately, the transmission will sometimes not shift into third gear. If I pull over, shut the car off and restart, it's fine. It does not happen all time. Last week I was cruising at 72 miles per hour and the car shifted down to second. I pulled over and just started over and it was fine. If it was the transmission, wouldn't it happen all the time? I suspect it is the sensor. Also, the cruise control stopped working. I replaced the fuse but still nothing. What are your suggestions?
A When the transmission will not shift out of second gear, it is most likely operating in the "limp" mode, meaning either an electronic issue such as loss of the speed sensor signal or a mechanical or hydraulic issue such as low hydraulic pressure. Because of the loss of cruise control, I would scan for a speed sensor issue and physically inspect the electrical connections on the transmission.
Q I have a 2005 GMC Envoy SLT that I bought new. It has steering wheel controls for the stereo, trip odometer, fan speed, etc. Several of these switches do not light up at night. Are there replaceable bulbs or do I need to replace the entire switch? Does the steering wheel come apart to replace these?
A According to GM service information, the bulbs in the steering wheel controls are not serviceable, meaning the complete switch assembly must be replaced. However, my ALLDATA automotive database pulled up GM service bulletin 04-08-45-010 dated September 2004 that identifies a poor connection at "ground splice pack G201" on the right side of the front console as a possible cause.
To replace the switches, the steering wheel must be removed, which involves safely disabling the air bag -- a job best left to a professional.