Here are answers to all your questions about only changing your oil once a year

Four-hundred emails.

That’s what was in my inbox Monday evening after my article on synthetic oil changes hit DeseretNews.com. I guess Utahns are really hungry for better ways to change their oil because I know my writing isn’t quite that captivating.

Actually, I am both flattered and gracious for the response the article received. I have always enjoyed educating people on the things I am knowledgeable about. Being both a user and dealer of the products I am referring to (full disclosure: I deal Amsoil), I speak from experience on what a high-quality synthetic can do for your engine. It's also really nice to see such an interest in something as mundane but relevant as changing one’s oil. Savings can often be found all around us if we just know where to look.

There is simply no way I can personally respond to all of the inquiries I received. So I have been asked to write this follow-up article to hopefully answer most if not all of the questions submitted by DeseretNews.com readers.

Click here for the original story.

Let's dive in:

Can all synthetic oils go 20,000 miles or one year?

No, they can’t. Very few oils are actually fortified with the correct base additives to go this far. Mobile 1 has an extended drain version that is rated up to 15,000 miles. The brand I use, Amsoil, makes a Signature Series product that is a "true" PAO-based oil that is rated for 25,000 miles/1 year. Being conservative I choose to back that off to 20,000 miles, which has worked well with my vehicles and my customers' vehicles, many of which are in commercial service.

Why can’t the oil go longer than one year if you have less than 20,000 miles on it?

Because oil is degraded by both “use” and “time.” Oil that sits in your oil pan is exposed to moisture in the form of humidity. It is also holding contaminants from your engine: dirt, carbon, diluted fuel, etc. Regardless of how good your oil is it cannot stand up to these conditions indefinitely.

Can high-mileage engines that have used conventional oil safely switch to synthetic oil?

Yes — with a disclaimer. There is absolutely no problem with compatibility between synthetic and conventional oil and you will certainly receive all of the benefits that synthetics have to offer, regardless of vehicle age. The disclaimer comes from the fact that a high-quality synthetic actually cleans up the mess that conventional oil can leave behind. A high detergent synthetic can remove deposits that have built up around engine seals, thereby causing small leaks. This is where the “synthetics-cause-oil-leaks” myth comes from. They don’t “cause” leaks, but they have the ability to clean out dirt that is currently sealing an old engine. This is actually a rare occurrence, so you need to decide if you want to make the switch. My advice would be this: If you have been changing your oil regularly and your engine is pretty clean, consider going for it. I have personally seen very few vehicles start to leak after we switched them over.

Will extending my drain intervals affect my warranty?

No, it won’t. According to Amsoil, in order for a manufacturer to legally deny you warranty coverage of your vehicle where you have been extending your drain interval, they would need to prove that the failure is “directly” related to a failure of the oil, which just doesn’t happen with today’s oils — conventional or synthetic. Service managers will scare you by saying your engine will not be covered simply because you are extending your drain intervals. Be sure to remind them that saying that to you is actually illegal. That usually quiets them down.

But my car is telling me it’s time to change the oil. Should I?