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Motor Oil

I was told by our local auto parts store clerk that once you switch to synthetic motor oil you can’t switch back to conventional oil because it will ruin the engine. Is that true?

Not true. You can switch back and forth all you want without doing damage to anything. Next time you see this counter person, ask them what happens if you use a synthetic blend motor oil?


I’ve heard of people switching back and having problems with leaks and burning more oil. I don’t think it will completely kill the engine!

Have you heard any first hand accounts of this? Don’t always believe what “they” say. Changing the weight of the oil might change the rate of any leaks you have, but that’s about it.

No, it is not true. As long as your owner’s manual does not specify synthetic (some do) then you can switch back and forth to your heart’s content.

For a good primer on oils, visit

another reason to question and inquire and not trust a store clerk

Do you mean to tell me that someone working for minimum wage at an auto parts store is not an accurate source of technical information?

I am shocked!
Shocked, I say!
(With apologies to those who wrote the screenplay for Casablanca.)

You referred to a CLERK, a person who rings stuff into the cash register when you buy it. He may have worked at 7-11 selling slurpies the week before. If that person was a qualified mechanic we would give you a detailed answer why he’s wrong. In this case, the clerk’s comment is PURE DRIVEL with no technical or scientific basis whatsoever.

What you should not do, however, is put thin synthetic oil (0W20)in an old, poorly maintained car with a worn engine. That will result in heavy oil consumption, and quick failure. But you know that already.

The truth is some really good mechanics out there believe it also.

There were some problems back when synthetic first came out, but it is no longer a problem. Switch as much as you like, as long as you use an oil that meets the specifications listed in the owner’s manual .

This is the same argument I put forth when I speak poorly about starting and charging system testing by the same people.

I was susprised by a clerk at Office Depot once. We were talking about what classes each of us were taking this semester and the clerk had already completed many classes I was struggling in. I learned not to judge just because the person was at the time a low paid low responsibility clerk.

The ONLY problems with earlier synthetics was they’d sometimes cause some leaking. HOWEVER even back then you could switch back and forth without any problems.

Interesting story. I have two of my own.

Many years ago as a quality Engineer I was assigned to a highly classified project working on control systems for the Cruise and Harpoon missile systems. We were put in a seperate concrete block walled-off area behind a cypher-locked door. We also hired an elderly gentleman to sit behind the door and act in a security capacity…and to get us pencils and coffee. He was a very nice old fella…who read the Wall Street Journal every day at lunch. I felt sort of sorry for him. When I got to know him I learned that he was a retired restauranteur from NYC, very wealthy, owned a successful chain of restaurants, whose wife had passed away and he took the job just to get out of the house and get some contact with people.

I myself have a confession to make. Due to some road bumps along the way these past few years, including a heart attack, I now work at a job where I often help people from behind a counter and most people who don’t know me think I’m a clerk. I don’t mind, some of my favorite people are clearks. Besides, my paycheck is not that of a clerk. It surprises people when I go into technical dissertations.

I’ve learned not to judge by appearances. But Ive also learned to check and confirm things through proper resources.