Question: I'm told by a trucker friend that it's dangerous to store a fire extinguisher inside a car that is parked in the sun. Is that true?
Answer: The trucker is wrong. After all, fire extinguishers are designed to fight fires, which are hot. What good would it do for an extinguisher to blow up when the temperature reaches nonlethal levels? You can bet that it gets a lot hotter inside a burning house than it does inside your car or truck on a sunny day.
If you are shopping for an extinguisher, you should look for one that displays the Underwriters Laboratory label. The laboratory requires that extinguishers can be safely stored at minus-40 to plus-120 degrees, a standard that is sometimes posted on the extinguisher.
But the laboratory also requires that extinguishers survive 175 degrees for seven days, which is not normally disclosed in product information. A quality, UL-listed extinguisher has a steel cylinder that is designed to withstand six times its normal pressure without bursting.
If you want to be cautious, you should store your extinguisher near the floor and out of the sun. It will stay a lot cooler than the temperature near the roof line.
The far more serious issue with fire extinguishers is whether you can safely use them if your car or truck does catch fire. Obviously, you don't want to be standing next to your vehicle when the gas tank blows.
Don't ever raise the hood of a burning engine. It could flash or explode in your face.
And if a fire has engulfed your vehicle, do not attempt to put it out.
All too often, the first instant you realize you have a car fire is when you see the paint on your hood bubbling up. You may think that it's only a minor fire and that you can put it out. In fact, the engine is burning up and the flames are limited only by the lack of oxygen under the hood.
An extinguisher might be useful, for example, to put out a fire that starts in the interior of the car. If a cigarette falls and ignites papers or carpeting, you might safely be able to extinguish a small fire.
Q: I drive very little, usually less than 7,500 miles per year. But my owner's manual advises me to change the oil at least every six months. Why? Oil has been in the ground for millions of years, so why should an extra six months make any difference in my crankcase? --D.X.
A: Oil companies will all tell you that you're making a big mistake by only changing your oil once a year, even if you are well under the recommended mileage.
Oil in the ground is in a stable environment, far different from the conditions inside your engine.
Here's the theory behind setting a limit on the length of time oil is in your crankcase: Lightly used engines develop condensation because they seldom get hot enough to burn off the water that normally builds up from engine blow-by. Also, the other contaminants that form inside the crankcase of your engine, including mild acids and sludge, will do a fair amount of damage.
But a number of mechanics offer different advice. They suggest that if you have a clean-running engine and you use your car irregularly (but take long trips when you do use it), then you can safely use your oil for more than six months.
A common recommendation by auto experts and mechanics is that if you are going to store your car for an extended period of time, you should fill the crankcase with clean oil. In this case, you are relying on aging oil to provide protection for the inactive engine.
What you don't want to do, however, is use the car for a one-mile trip each day and decide that you will wait 365 days to change the oil. In fact, you can make a strong case that in this kind of usage, it would make sense to change your oil more frequently than every six months.
Ralph Vartabedian cannot answer mail personally but will attempt to respond in this column to automotive questions of general interest. Write to Your Wheels, Business Section, Los Angeles Times, Los Angeles CA 90053. Via e-mail: email@example.com.