Headlight ‘just keeps blowing out’

Dear Mike: My buddy has a ‘97 Ford Escort, and I help him with his maintenance. I have replaced his left headlight bulb three times in the past year, and it just keeps blowing out. I am very careful not to touch the bulb when installing it. What am I doing wrong?

A: Maybe nothing. To rule out any issue with the car, start with a voltage check, specifically the charging system. Check the charging voltage at the battery, with the battery fully charged and the engine warm and running with all loads turned off (don’t forget the heater fan). Your voltmeter should read no more than 14 volts or 14.5 volts, tops. Actually, I’d expect to see 13.5 volts to 14 volts once everything is warm. If it’s any higher, you’ve got a bad voltage regulator or a bad ground somewhere in the charging circuit.

But that’s unlikely. I suspect if there were a problem with the electrical system, other bulbs would be popping like flashbulbs at a celebrity wedding reception.

So, you’re probably installing these bulbs with some surface contamination. As an aside to those who haven’t gotten the word, or who missed the fine print on the packaging on those $20 headlamp bulbs, don’t touch the bulb’s glass envelope with your bare fingers.

The quartz glass used in these bulbs has a very high melting point. The bulbs run extremely hot. That’s necessary for a quartz bulb to maintain brightness throughout its life span. The heat causes the oils in your fingertips to carbonize on the surface of the glass. The darker carbon absorbs more heat, causing a hot spot, and the differential expansion eventually breaks the glass. Within a few minutes, oxygen gets in and fries the filament. And yes, contamination of the surface by other substances can do the same thing. That’s why I always clean new bulbs, even if I’ve just removed them from the protective packaging.

Rubbing alcohol and some tissue or cotton are all you need. And when installing the bulb, keep it clear of any greasy under-hood wires or the lip of the headlamp housing. Wearing clean rubber gloves also helps.

Dear Mike: I have a 1999 Mercury Sable with 75,000 miles. While driving at 70 miles per hour with the Cruise Control on, I noticed the speed of the car was going up and down a small amount.

Suddenly the speed went wild; it kicked it back a gear, and the speed and RPM increased until I hit the brake to disengage the Cruise Control. Then I noticed the speedometer was going from 10 miles per hour to 50 miles per hour. The only way I could judge my speed was with the tachometer. The speedometer gradually slowed down and after 60 more miles it returned to normal. After the car sat for five hours, it was back to normal.

Does the speedometer have a cable that controls the speedometer or is it controlled by computer? When this happened I almost panicked. I actually lost control until I realized what was happening. I’m afraid it might happen to my wife on our icy Michigan roads.

A: It’s pretty obvious to me there’s something wrong with the speedometer, which is electronic. Get this fixed before somebody gets hurt.

Dear Mike: What is your opinion of filling up car tires with nitrogen to improve both wear and gas mileage? Is it worth the $30 the local dealership is charging for this type of service?

A: Nitrogen is good, at least partly because it is devoid of any moisture. But it’s not $30 good.

Dear Mike: My wife has a 2001 Pontiac Grand Am GT 3400. The car runs fine but it has a slight oil leak. It’s not a whole lot — just a couple drops about the size of a quarter. I’m thinking that I need to replace the oil pan gasket, from what I can see when I crawl under the car. There are no signs of leakage if I look at the engine from the top, just the bottom. It looks like oil runs down one side of the oil pan that creates the drops on the floor. Any suggestions?

A. Start by tightening all the bolts that hold the oil pan on. If that doesn’t do it, you may have to replace the gasket.