Dear Tom,

I just bought a 2009 KIA Optima. The owner’s manual says I should use 5W20 oil in the engine. My dad used to fix cars and he said that this oil is too thin and that I should use “Straight 30 weight” in the winter and the 5W20 in the summer. Is he right?

Sandy from Salt Lake City, UT

Sandy

Gently tell your dad to stifle himself. Use the 5W20 oil in your KIA. The carmaker selected this oil because the engine operates under tight operating tolerances. If you put heavier oil in it then you’ll damage the engine, not to mention void your warranty should the need arise to make a claim. Years ago dad’s advice might have been acceptable, but now it’s way outdated.

Tom

Several years ago a woman called my radio show with the same question. However, she had already followed her husband’s advice and the engine in her new Ford seized due to lack of lubrication. She had to buy a new engine on a car that had only 25,000 miles. Too bad. Here are some things you should know.

What Type Of Oil Do I Use?

The answer to this question is in your owner’s manual under the maintenance schedule. The carmaker outlines what weight (viscosity) to use. If it says 5W20, use it. Carmakers make engine oil recommendations based on extensive lab testing, road testing, and research done in conjunction with petroleum companies. You can rely on the recommendation because it’s based on a lot of research.

Should I Change The Weight Of The Oil Based On Time Of Year/Temperature?

No. Multi-viscosity oils are designed to adjust their rate of flow (weight) based on outside and inside engine operating temperatures. When you read an oilcan that has a viscosity rating of 5W20 it means that the winter flow rate of the oil is 5 (thinner) than the summer flow rate (thicker). Multi-viscosity oils thicken up in the summer when the temps are hot and oil tends to thin out. When it gets cold they thin out in order to maintain optimum flow rate in all temperatures.

What About Synthetic Oil? Can I Use It?

In most cases you can switch over to synthetic oil. However, consult your owner’s manual before switching to make sure there are no caveats. I like synthetic oil because it is chemically fortified to withstand the rigors of the internal combustion engine environment. While it is not impervious to, it is highly resistant to viscosity breakdown from heat, friction, and chemical contamination. Synthetic oil flows better in winter and provides superior lubrication and protection in the summer when most oils break down under intense heat. If you switch over, just make sure you use the viscosity recommended by your carmaker.

How Often Should I Change The Oil?

When using good quality synthetic oil, change it every 5 - 7 thousand miles or six months, whichever comes first; and make sure to change the filter. When using petroleum-based oil, change it every 3 - 5 thousand miles or three months. As with synthetic, change the oil filter with a high quality filter every time you change the oil. Why the longer drain intervals with synthetic oil? It’s tougher, therefore you can go longer between drain intervals. Based on my research of synthetic engine oil, AMSOIL is number one and Mobil One is number two.

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