Today: why engine oil has gotten lighter in recent years.

Dear Car Talk

Dear Car Talk | Aug 01, 2010

Dear Tom and Ray:

I recently was advised to use a much lighter weight of oil than I am used to using. I was told I should use 5-20 weight oil in my 2007 Pontiac Solstice convertible. I grew up in Minnesota, where this was considered "winter weight" oil. For summer, we all went up to 20-40 or 30-50 weight. Now I live in northern Georgia, and 5-20 weight just sounds awfully thin -- especially in summer. So, is the mechanic trying to ruin my engine? Or have things changed since I was 16? Thank you!

-- Richard

TOM: Things have changed since you were 16, Richard. I mean, start by taking a look at your hairline.

RAY: Oils have changed, too. They've gotten significantly better in the past 30 years. The improvements in their ability to lubricate and resist high-temperature breakdown have allowed manufacturers to make engines that run on these lighter-weight oils. And lighter oils mean less internal engine friction, which means better gas mileage.

TOM: That's why Pontiac itself suggests you use 5W-20 in your Solstice. You can use a heavier oil if you want to, but you won't get the intended fuel economy, and in cold weather, you won't get the engine protection that your manufacturer is counting on.

RAY: So I'd use 5W-20, Richard. Since it's the manufacturer's recommended oil, it certainly won't do any harm to your engine.

TOM: If you're feeling adventurous, you can try some 5W-20 on your hairline, too. It probably won't grow hair, but from a distance, that black smear might be mistaken for a patch of new growth.

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