craig1black via Flickr
Due to the overwhelming response to my article on synthetic oil changes, here are answers to questions from the 400 emails that showed up in my inbox on the topic.

Four-hundred emails.

That’s what was in my inbox Monday evening after my article on synthetic oil changes hit 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 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?

I shudder to think what our cars will be telling us in a few more years! Seriously though, your car is simply telling you that you have driven a set amount of miles since the timer was reset. More advanced cars actually have a complex algorithm that factors in mileage, idle time, operating temperatures, etc. Regardless of methodology, your car is assuming that you are using the most basic minimum specification conventional oil. When using the grade of oil I do this is simply not a concern.

So how do I reset the oil light?

My favorite answer to anything I don’t know: Consult Google. A quick search online will render countless articles on how to reset your particular vehicle’s maintenance light.

How do I know if an advertised synthetic is a “true” synthetic base?

Unfortunately this is a tough one. I have spent hours researching this and it is not easy to find out. Basically, oils that are true synthetics — those made with Group IV base stocks — will typically be advertised as such. They are proud of that fact, so they usually tell you somewhere in their marketing material, but not always. I do know that Amsoil and Redline are true synthetics. I happen to be partial to Amsoil for many reasons — the diversity of its product line being one of them. I have also had tremendous success with my vehicles my customers' vehicles and equipment using Amsoil's products.

Is there any situation where you don’t suggest synthetic oil for my vehicle?

Yes, two situations; if your car is either burning or leaking oil. In either case you will be having to top off your oil frequently, which undermines the savings you are trying to achieve. Aside from that I adamantly recommend synthetics. If you have an older vehicle that you want to run forever, I would make the switch. If a seal starts leaking for the aforementioned reason than you know you had a bad seal that needed to be addressed anyway. Replace the seal and start enjoying the future savings and convenience. If your car burns oil, you need to decide if it’s worth fixing so that you can receive the benefits synthetics offer.

I thought mechanics check out your car during regular oil changes to catch problems early on?

They do — at least they should. I know we did that in my shop. An oil change is the perfect opportunity to get under a customer’s car and identify issues that are developing. In no way am I suggesting you skip this. You just don’t need to pay for an oil change to get the inspection. My suggestion would be to have your mechanic change your oil at the 20,000-mile/1-year mark and then go in for an “inspection” six months later. A good repair shop should offer a complimentary inspection for its customers. That way you’re covered and don't pay for an unnecessary oil change. In my opinion, that’s being a smart consumer.

So where do I find the products you’re talking about for my specific vehicle?

Send me an email, and I will explain the products you should look for. In the future, I will have a site that explains more about these products.

I want to be sure anyone who is considering switching to extended oil drain intervals realizes one very important detail: You must check your oil at least once a month! Going 20,000 miles/1 year on an oil change is a great convenience, but you absolutely must check the dipstick regularly. If your oil levels drops during that period, which is not uncommon, you will want to add a little back into your engine to ensure the proper level on the stick.

I have been asked to write additional automotive articles. Please feel free to leave comments below telling me topics you would like to see me address in the future.

Zak Anderegg opened Utah’s first full scale do-it-yourself repair shop in 2009, which was featured on numerous local TV networks. He also works with business fleet managers. Feel free to email any questions you have to