Today: What's Wrong With Daniel's 1979 Fiat?

Dear Car Talk

Dear Car Talk | Feb 25, 2014

Dear Tom and Ray:

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.

-- Daniel

TOM: Most Fiat Spider owners would kill for heat like that in the winter, Daniel. 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, Daniel. 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, Daniel.

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, Daniel? 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.

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