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1999 Mercedes-Benz SLK-Class - oil change frequency

Synthetic oil change frequency?

In 2013 I bought my wife a1999 Mercedes 230SLK with just under 25,000 miles on it. The car now has just over 51,000 miles. It uses synthetic oil. It has been at least 2 years since I have changed the oil because every time I check it the oil on the dipstick is the color and transparency of honey. Do I really need to change synthetic oil per the calendar when there is no sign of contamination?

Yes , here let me do that again " YES ". The most you should do is 5000 miles or 6 months . The manual might say different but going 2 years is insane.

That car should have a maintenance computer, up to 15,000 miles or one year for oil and filter change. Synthetic oil is required.

A Mercedes dealer or website may give you updated recommendations for oil type and recommended change intervals. My Honda dealer told me the new updated recommendations for my 1999 Civic a few years ago and I have followed that with no problems. Oils have changed since 1999, and so has engineering knowledge.

Simple . . .

every 10K the car will want a service, a small service followed by a large service, and so on

Anyways, the manual also states that you must change the oil yearly, even if the service reminder message hasn’t yet popped up


Unfortunately, both water and acid are colorless, so contamination with those liquids could allow your oil to look “normal”, even if it is not. There is a very good reason why every car mfr specifies changing oil at least once a year–even if very few miles have been driven.

Generally you cannot tell the condition of motor oil simply by looking at it. My mom has a 2003 CLK 430. It gets an oil change once a year, with Mobil 1. She only puts around 7k-8k miles a year on it, And it holds around 8 quarts of oil, so I’m comfortable with that OCI. You forgot to mention that your SLK 230 is supercharged. I would definitely not run 2+ year OCI’s on any car, let alone one with forced induction.

There are companies that do oil analysis. You send a sample of the oil, they tell you about its condition and list contaminants and their meaning or effect. If you knew the oil was not hurting your engine, you could decide to leave it in and have some peace of mind about it.

all of the 1999 SLK230 models sold in the USA were supercharged

All the 1999 SLK 230’s sold anywhere were supercharged. They didn’t do a N/A version of the 2.3L in the SLK. They had a N/A 2.0L in Europe though

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