Why have manufacturers put hotter thermostats in their engines?

Dear Car Talk

Dear Car Talk | Jan 01, 1997

Dear Tom and Ray:

Why have automobile manufacturers put hotter thermostats in their engines? The old thermostats used to be 160-180 degrees. Now they're 20 or 30 degrees hotter than that. Why would they do this? It's fairly common knowledge that heat is the worst enemy of engines and oils, isn't it? -- Larry

TOM: Ah, the age-old question about heat, Larry. Enemy or friend? It depends if you ask Lawrence of Arabia or Nanook of the North, doesn't it?

RAY: It's true that heat can be hard on an engine, but in the opinion of most automotive engineers, the benefits of hotter-running engines far outweigh the negatives.

TOM: Engines burn fuel more cleanly and efficiently at higher temperatures. With the coolant at 195 degrees (instead of the more traditional 170-180 degrees), for instance, you'll get better performance, less pollution overall, and greater fuel economy.

RAY: And while 25 years ago, using a 195-degree thermostat might have shortened the life of the engine, oils have gotten much better over the years. Now they perform much better in extreme heat, and give the engine plenty of protection in those temperatures without breaking down.

TOM: So the whole engine is really optimized to run at 195 or 200 degrees now. And at that temperature, no harm is done
RAY: And believe it or not, if you put a cooler, 160-degree thermostat into a modern car, you wouldn't be helping it at all. In fact, you'd just confuse the computer and cause the "check engine" light to come on.

TOM: It would be like lowering the temperature 30 degrees at Waikiki beach during the peak of the tourist season. It just wouldn't go over well, Larry.

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