Could speeding in a four-speed car do damage to my little four-cylinder engine?

Dear Car Talk

Dear Car Talk | Mar 01, 1995

Dear Tom and Ray:

I have a "hypothetical" question for you guys. Suppose a person had a 1992 Dodge Colt with four cylinders, a four speed standard transmission, and she gave it regular oil changes. Now suppose the hypothetical owner drives just a little fast (say, hypothetically, 75 mph) on a fairly regular basis on the highway. Keeping in mind that it's a four-speed and not a five-speed, just how bad would this be for the hypothetical little car?

TOM: There ARE some disadvantages to going that fast, Jan, aside from the hypothetical speeding tickets, hypothetical insurance surcharges, and the hypothetical license revocation.

RAY: The non-hypothetical disadvantages are that, at higher speed, your engine works harder and runs hotter. This wouldn't be the case if you were driving this car at 75 with a big eight cylinder engine. But with a little engine like your's, 20 miles an hour can make a difference.

TOM: Here's why. At 75 miles per hour, the wind resistance is almost double what it is at 55 miles per hour. So your little, four cylinder engine is going to have to work much harder to keep the car going 75. And because it's such a small engine, you're really pushing its limits when you get up to 75 or 80 mph. And when you run an engine near the limits of its cooling and lubrication systems for extended periods of time, things definitely wear out quicker.

TOM: How much quicker? 5%? 10%? It's hard to say. But when you ask a small engine to do a lot of extra work, the oil breaks down sooner, the bearings wear out quicker, head gaskets deteriorate faster, valves burn out more frequently. Essentially, you accelerate the process of turning this car into a heap.

RAY: Now, maybe that's what you want. Perhaps you see yourself, hypothetically, in a Jaguar XJS V-12 Convertible instead of a Dodge Colt, and you're just trying to turn the Colt into junk as quickly as possible.

TOM: But since your car payments are probably NOT hypothetical, it might make sense to ease off the accelerator a little bit.

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