Although the price of gasoline is heading downward to levels that are merely outrageous rather than insane, consumers are still rightly concerned about various issues.

Here are two questions raised by readers that cover important issues worth explaining in greater depth:

Does driving on ’empty’ hurt the engine?

Dear Terry,

With gas as expensive as it is, I’ve been driving my car until the gas light comes on. But this goes against everything my dad taught me.

He said to never let your gas go below a quarter of a tank, otherwise you could get dirt in your engine and ruin your car.

Is he right, or does he just not want me to run out of gas?

— Riding Dirty

Dear Riding,

Dear old Dad may have been right about many things, but when it comes to modern vehicles, he has this one mostly wrong.

Almost all cars have their fuel pumps installed inside the gas tank and the pump picks up the fuel from the lowest part of the tank, so you can get almost every last drop from the tank.

If there is a lot of dirt and debris — say, from a corroding fuel tank — that gunk would normally settle to the bottom and be picked up by the fuel pump regardless of how much fuel was in the tank.

But modern fuel pumps have a protective screen or porous sock-like cover that catches any contaminants before they enter the fuel system. And those small bits that might get through would normally be caught by a second filter closer to the engine.

Back in the day, when manufacturers were churning out cars with very little rust protection, it was possible that after four or five years there could be some corrosion on the inside of the gas tank that could result in sediment. But most gas tanks these days are not prone to such issues.

Where your dad may have been right is that you should always try to never run out of gas. That fuel pump inside the gas tank relies of the gasoline to keep it lubricated and cool, and if you frequently run out of gas you could cause the pump to fail.

The good news is that the “low fuel” light comes on when there’s anywhere from 1 to 2 gallons left, which is plenty to keep the pump safe.

So it’s OK to run the tank down to where the warning light comes on, but you should then get gas as soon as possible.

Does shutting down in traffic save gas?

Dear Terry,

When is it worth it to turn off your car to save gas? A draw bridge near my home has a sign that says to turn off the engine while bridge is up, but will it waste gas to start up the car after the bridge goes down? And what about turning it off in drive-throughs or when waiting at the bank?

— Fussy Fuels-a-lot

Dear Fussy,

This is a lot like the question of whether you should turn off the light in a room when you leave for just a few minutes. The notion is that turning the light back on may require a surge of electricity greater than the electricity the light would consume if left burning.

I can’t speak to the light question, but there are times when shutting down your car while idling will save gasoline.

First, all vehicles built since about 1990 have electronic fuel injection that much more efficiently doles out the gas to the engine. When you start today’s cars, there’s not a big rush of fuel to a carburetor.

So anytime it looks like you’re going to be idling for more than 30 seconds, you can save a bit by turning off the engine.

Some practitioners known as “hypermilers” turn off the engine at every stop light, then quickly turn it back on when the light goes green. They claim fuel mileage increases of 30 percent or more, but I think that’s a lot of work and perhaps imparts greater wear on the starter mechanisms and the transmission, which could result in eventual repairs that would outweigh any savings at the pump.

Also, if you live in a warm climate, you make find that going without air conditioning while the engine is stopped is not worth the savings.

No magic can bail out delinquent driver 

Dear Terry,

I purchased a Honda Element in May 2007, when I had a great-paying job. I have lost that job due to having to move because of domestic abuse. I am living in a small town with two boys and I am having a very hard time finding a job.

In short, I can no longer afford my car. My monthly payment is $495. My mother signed on the loan with me and I have ruined her credit now due to the fact that I have fallen behind on my payments.

How do I get out of my loan and still save my mother’s credit? I truly cannot afford a $500 car payment. I still owe $22,000, yet my Blue Book value is only $14,500. Please, can you give me any advice?

— Jami

Dear Jami,

I wish I could offer you and others in similar situations some magic way to get out of a car loan with no financial damage. Unfortunately, there’s little that can be done.

Unless your mother can take over making the payments until you get back on your feet, the lender is likely to repossess the car, which will hurt yours and your mom’s credit ratings.

High-risk borrower doomed to poor rate 

Dear Terry,

I have just filed for bankruptcy (due to a subprime mortgage debacle) and I am in need of another car. How can I re-establish my credit to get a car loan without getting completely ripped off with an outrageously high interest rate?

— Daisy

Dear Daisy,

It’s likely that the only lenders who will offer you a loan will be those that specialize in high-risk borrowers — of which, by virtue of the bankruptcy, you’re now one.

I have seen interest rates from these places running to more than 20 percent. My best advice it to get the least expensive car possible, pay it off as quickly as possible, and then look for something better when your credit score improves.

Wacky offer could fleece car shopper 

Dear Terry,

I have a 2002 Chrysler Sebring convertible in very good condition with only 34,000 miles. The high Blue Book value is $8,000.

Would I look like an idiot if I went into a Toyota dealership with it as a trade and told them I wanted $12,000 for it and was only willing to pay $1,000 over sticker for a new two-wheel-drive, four-cylinder Dodge Pickup Club Cab with all the bells and whistles?

— Laura

Dear Laura,

I don’t know exactly where to begin to unravel this muddle.

First off, high Blue Book value generally means the retail value of a vehicle — what a dealer would charge to sell it. So you want the dealer to pay you $4,000 more than what the dealer could reasonably sell the car for?

Then, you want to pay $1,000 over the window sticker for a pickup, when you should be negotiating for a purchase price under the sticker?

If you go into a dealer with this sort of wacky deal, you’re going to get fleeced. The dealer will manipulate the numbers so that you will end up paying more than you should.

Check you car’s trade-in value and negotiate the price of the truck before even mentioning the trade. Then, see what the dealer will give you for your car. You may be better off selling the Sebring on your own.

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