Felicia's Car Can't Take the Heat

Dear Car Talk

Dear Car Talk | Mar 17, 2015

Dear Car Talk:

We live in the Southwest and have a 1992 Lincoln Town Car, which is much loved by my husband. The only problem is that it likes to die when the temperature is above 96 degrees. We will be traveling for over 30 minutes and boom, it dies. It starts again in about 20 minutes, but if it is still hot, it will soon die again. This also happened once in cooler weather when we had been driving in the mountains for two hours. We've been given theories such as vapor lock and boiling fuel, and advice that included clothespins, but I don't feel comfortable betting my safety on clothespins. I hope you can help us. Thank you.

-- Felicia

Don't discount clothespins, Felicia. I always keep a couple in the glove box. I used to clip them on my nose whenever my brother was in the car.

Clothespins aside, your first step is a little detective work. In order for the engine to run, it needs three things: Air, fuel and spark. I'll assume that air is not a problem, since you continued breathing long enough to write to us. So you have to determine whether the engine is dying because it's losing fuel or losing spark.

If you were one of our customers, we'd lend you a little inductive test light and show you how to use it. If you open the hood and just touch the probe of the test light to any of the spark-plug wires while the car is running, the light will flash, indicating that electricity is pulsing through those wires. That tells you there's spark.

What we'd instruct you to do is, next time the car dies, open the hood and touch the test light to a spark-plug wire. Then have another person try to start the car. If the light flashes, you're getting spark. That means the problem is fuel.

If you try to start the car and the test light doesn't flash, then we know it's a spark problem. By knowing which of those it is, we can save you a lot of time and money in trying to figure it out.

If the test tells us that the problem is lack of fuel, we'd suspect either the electric fuel pump or the fuel pump relay.

If you had no spark, we'd suspect one of the electronic ignition components, like the electronic ignition module, the coil or the hall-effect sensor.

But start by finding a mechanic who's willing to work with you to narrow it down. If you need help finding a mechanic you like, try searching our Mechanics Files, which is a database of mechanics who are personally recommended by other readers and radio listeners of ours. Good luck.

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