Post and Courier
August 30, 2014

Car Talk - Faulty catalytic converter, ignition timing, heat shield: Whatever the case, it's heating the pedals something awful

Posted: 03/01/2014 12:01 a.m.

Q.

Every time I drive my 1979 Fiat Spider, excessive heat comes from the engine compartment to the area by the pedals. What's causing this, and can it be corrected? During the colder months, it's not so bad. But during the summer months, it's pretty unbearable. Thanks.


TOM: Most Fiat Spider owners would kill for heat like that in the winter. I had to wear six pairs of Bronko Nagurski long underwear whenever I drove my Fiat in the winter.

RAY: Yeah, but it's like Death Valley on four wheels in the summertime.

TOM: The exhaust system happens to run right behind those pedals and continues underneath where you're sitting. So my first guess would be that something's causing your catalytic converter to run hot.

RAY: When catalytic converters get old, the insides can deteriorate and get in the way of the exhaust flow. When that happens, a constricted converter can get very hot - over 1,000 degrees!

TOM: In fact, sometime when you're driving the car at night, wait until you feel your shoes melting to the floor. Then stop, get out and take a look underneath. You might actually see the converter glowing. They literally get red-hot when they're really plugged up.

RAY: It's also possible that the primary problem is not in the converter itself. Something may be causing it to run hot. For instance, if your ignition timing is very late, you'd have gasoline getting pushed into the exhaust system without first being combusted. Then, what happens is that the gasoline combusts inside the catalytic converter. And where there's fire, there are hot feet.

TOM: A bad fuel injector can cause the same problem, by injecting into a cylinder more gas than can be combusted and leaving some to be burned in the converter.

RAY: If it's none of that stuff, then it simply could be that your heat shield is missing.

TOM: Or your floor. Does your Fiat still have a floor? Mine didn't for the last couple of years.

RAY: Heat shields are thin pieces of metal that are fitted around the hottest parts of the exhaust system. They're designed to absorb and dissipate heat so it doesn't get transferred into the passenger compartment.

TOM: Or transferred onto the dry grass or old newspapers you park on top of.

RAY: And on a car this old, it wouldn't surprise me in the least if your heat shields are long gone, having rusted away and fallen off years ago. Like most of the car's other parts.

TOM: In either case, if you're really producing enough heat to make driving the car uncomfortable, it could be a fire hazard. So have it checked out. And until you do, keep some running shoes on the passenger seat just in case you need to make a very hasty escape.

Q.

So many of my friends evaluate the cost of a car trip only by the cost of the gas. But I know that the cost, given wear and tear on the engine, oil changes, tires wearing out, alignment, etc., is actually much, much higher. I know this depends on the car, but how much, on average, does it cost per mile to run a car?


TOM: Well, every year, the Internal Revenue Service answers that question. They want to know the value of one mile driven in the average car so they can let taxpayers know how much they can deduct for business use of their personal vehicle.

RAY: The number they came up with for 2014 is 56 cents a mile.

TOM: Now, let's say the average car gets 25 miles per gallon today, and the average price of gas per gallon is $3.50. That means that gasoline represents only 14 of that 56 cents.

RAY: And the rest - the other 42 cents - covers wear and tear and insurance.

TOM: In reality, that maintenance-and-repair figure will be even higher on pricier cars. Because if you're driving a Lexus or a Lincoln, the price of your maintenance, repairs, tires and even insurance is going to be even higher.

RAY: But that 56-cents-a-mile number gives you an idea of how much people underestimate the cost of operating a car when they factor in only the 14 cents' worth of gas.

TOM: So next time you drive your friends to the mall, you can try hitting 'em up for the full IRS reimbursement. See how that goes over. And be prepared to settle for a grande cappuccino.

Got a question about cars? Write to Click and Clack in care of this newspaper, or email them by visiting the Car Talk website at www.cartalk.com.