Creating a problem where none existed

Dear Bob: In August 2004 I purchased a new 2004 GMC Envoy. I drove the vehicle to Myrtle Beach, S. C., and when I was going through the Blue Ridge mountains the vehicle would pulsate when going down steep hills with the speed control set at 60-70 mph. It was as if the vehicle were braking to maintain the set speed. It only happened on steep grades, and the SUV performed properly at all other times.

I took it to the dealer and explained the problem, but could not duplicate the problem because there are no hills steep enough in Illinois, where I live. After keeping the vehicle for a few days, the dealer couldn’t duplicate the problem either. But he assured me that I had a 36,000-mile warranty and had a window of opportunity to get it corrected if needed.

My question is, corrected by whom? What options do I have in the mountainless Midwest before my next trip through the mountains? Is there a dynamometer or any test equipment that could duplicate the problem?

Sincerely,

— J.C., Belleville, Ill.

A: First of all, I don’t think you have a problem. Second, you shouldn’t be driving down steep slopes with the cruise control set between 60 mph and 70 mph.

Yes, your SUV was pulsating, and your self-diagnosis is exactly right: It was braking in order to keep the vehicle’s speed at the setting to which the cruise control was set. This is perfectly normal, because obviously the vehicle “wanted” to go faster than the set speed, because of the steepness of the downgrade.

I suggest that, on your next trip through the mountains, you turn off the cruise control when going down steep hills. It’s dangerous to use cruise control when going down sharp inclines, a practice that you’re specifically cautioned against in your owner’s manual.

You’ve created a problem where none existed by using cruise control in a situation in which it should never be used. I’m surprised that the dealer didn’t pick up on this and warn you against doing it.

Dear Bob: I read your column in The Middletown Times Herald-Record.

I have recently had the unfortunate luck of changing two flat tires, one for my daughter and one for someone I saw at a coffee shop. Both cars had “donut” spares, and both spares were flat.

I have told everyone I work with to check their spare tires, and I wonder if you could do the same. These space-saver spares don’t hold that much air, and it seems as if they leak quite easily. Given that the one I worked with needed 60-psi inflation, they would have to be filled at a garage — unless someone had a good bicycle pump and lots of stamina.

The point I want to make is that people should check the air in the spare. It would be foolish to have a flat and no spare, or a spare with no air.

Thanks,

— M.L., Kingston, N.Y.

A: Years ago, I remember, I read a study done by the California Highway Patrol that listed tire problems, including a spare with no air, as near the top of the list for problems that disable vehicles.

Many flats are unavoidable, but having no air in the spare isn’t. Each time you put air in your tires, you should also check the spare. A good quick-lube, or any shop that does tire work, should automatically check the air in the spare.

It’s such an easy thing to do or to have done, and it can avoid so much anguish in the event of a flat. It’s no fun to have a flat on a deserted stretch of road, only to find that your spare is also flat.

Don’t get caught with no air in the spare. There’s no time like right now to go out and check the air in yours.

AMERICAN DRIVERS FIGHT BACK

Here’s a tip that will help you get better gas mileage while fighting terrorism and cutting our nation’s dependence on Mideastern oil:

The colder the ambient or outside temperature, the worse your gas mileage will be. One of the contributing factors to this diminished fuel economy is the fact that cold air is more dense, and therefore increases aerodynamic drag. If you reduce your top speed a bit during cold months, you’ll help offset any mileage loss caused by the colder, dense air.

If a car travels at 50 mph on a level, straight, dry asphalt road on a windless day, at a temperature of minus 20 degrees F the car will use .06 gallons of gas per mile. At an outside temperature of 80 degrees F, however, that same car under the same conditions will use only .05 gallons per mile.

That sound like an awfully small amount. Translated into miles per gallon, though, this means that the cold-weather car will get approximately 16.66 mpg while the warm-weather car enjoys 20.0 mpg. That’s a difference of about 3.33 mpg, which is no small matter.