Synthetic oil change intervals

I recently married and my wife had a 1999 Chev Silverado truck. She has driven almost entirely highway miles on it and the Chev dealer had convinced her that she needed to change oil every 3000 miles. The manual specifies 7500 for this type of driving. I have now switched to synthetic oil and I think I have read that with this oil you can stretch the intervals even further.

I have been changing oil every 10,000 miles.


I also use synthetic oil in my 2000 Ford Explorer, but stick to the interval in my manual, which calls for 7,500 mile oil changes. Even with the extended protection on synthetic, 10,000 miles just seems too long. Plus, I only change the oil twice a year at my current rate.

Even tho synthetic oil maintains it’s lubricating properties longer than conventional oil, the oil still picks up dirt and contaminants that still need to be removed with an oil change. Keeping it in too long makes me nervous, as I envision that dirt and contamination acting like an ultra fine sandpaper on the rings and bearings.

On my '88 Supra, it gets conventional oil and changes every 4,000. It gets changed 3 times a year.

I recommend staying with the schedule in the owner’s manual. Both synthetic and dino oils are subject to the same particulates and dilution and contamination by blowby. While the synthetic has been shown in the lab to be less suseptable to heat damage and suffer less shear damage (due to its more consistant molecules), the goal is to prolong the life of the engine rather than the length between oil changes. Even if the synthetic does allow you to extend the time between changes, doing so defeats the purpse of buying synthetic.

I would stick to 7500 miles. However if you want to go past do some research over on you can find specifics of your motor.

Some engines are very hard on oil while others are easy.

This is “the post that never dies”! Just because you paid 2-3 times as much for synthetic oil, you can’t stretch the change iterval, since it is based on ADDITIVE DEPLETION and the ACCUMLATION OF NASTY STUFF. The base oil is only affected if the driving is extreme, such as heat, bearing load, extreme cold.

Motor oil is 25-30% additives and those get depleted just as fast in synthetic as in regular “dino”.

As others point out, for highway driving the 3000 mile interval is too short, even with dino oil. I would stick with the owner’s manual, and use 7500 miles for highway driving and 3000 miles for city driving only.

The only safe way to change oil every 10,000 miles (regardless of oil used) is when you drive non-stop back and forth from New York to LA at legal speed, and not towing a trailer.

Chev dealer had convinced her that she needed to change oil every 3000 miles

Warning - ADP (Additional Dealer Profit!)

The dealer have proved himself as more interested in his personal profit that providing proper service. I suggest your wife look for a good independent mechanic or maybe even a different dealer. That dealer is either knowingly lying or he does not know better, in neither case you don’t want to do business with them.

The owner’s manual is the authority.

Synthetic oils are very good oils. If it is not specified by the car manufacturer (see owner’s manual) then it is not needed, but I would likely go for synthetic anyway. However better or not, there are too many other factors relating to oil to stretch out the changes.

The limiting factor for engine oil life is combustion blowby. Leakage past the piston rings. Were it not for that, 30,000 mile / 3 year oil changes would be possible. Some engines have more blow-by than others. As engines age, blow-by increases. At some point, the oil becomes so contaminated with combustion byproducts it loses it’s ability to protect the engine and the dreaded “sludge” starts to form. Some people think synthetic oil can accommodate significantly more contamination than mineral oil. But there is no basis for these beliefs…Good Luck at 10,000 mile change intervals…Some engines might survive this and others might not…

I just changed the synthetic oil on our new 09 at 12,400 miles with the computer showing 3% oil life remaining. That would calculate out to 12,783 miles to change if I did not do it early. The car was new this summer to give an idea of the time. Our driving is mostly long trips. I would estimate the driving time as 50% local and 50% high speed. Frequent cold starts deplete the oil faster. I always drive at least enough to warm the engine thoroughly.

7500 should be fine but you must also change at least once per year minimum according to my owner’s manual.

“I just changed the synthetic oil on our new 09 at 12,400 miles with the computer showing 3% oil life remaining.”

What does a computer use to determine when oil should be changed, other than mileage and possibly time?

Does your owner’s manual say to wait as long as 12,000 or more miles before changing the oil?

What model car do you own?

I have a 2000 Blazer with 109k miles. My personal preference is for a 4k - 5k interval for oil changes, usually 4k. The Blazer also has a 7.5k interval, I would not be comfortable going that long under any conditions. Especially now that the Blazer is starting to use oil between changes.

There are a lot worse things a dealer can do than recommend 3k oil changes, even my mechanic of 16 years puts 3k/3 months on the reminder sticker after an oil change.

Most importantly, since the wife is always right and changing the oil every 3k keeps her and the truck happy, then best leave this one alone. It’s a small price to pay for domestic tranquility in the long run.

Ed B.

Good post, Caddyman! Frequent oil changes keeps the rings clean (and sealing properly) and minimizes cylinder wear due to nasty contaminants. Once blowby starts, it’s downhill rapidly!

Seems like extended intervals would be possible under monitored driving conditions(oil life monitor) with a large oil sump(8qts+) like BMW/MB? Or no?

Sorry, but that makes absolutely no sense. You have a $30-40,000 car, and don’t change oil for 13,000 miles? You saved what? Maybe $50 for a couple of dealer oil changes? I very seldom let the oil change monitor go past 50% before changing, but 3% on a new car? Shame shame.

Like I said before, I would not buy a used car where the guy used syn oil just for this reason. People think they can go without changing oil because they pay more for it and it lubricates better. Stick to standard oil and change at 5000. Or use syn oil and change at 5000. Your choice.

Owner’s manual defers to the computer except for the once per year mmaximum time. I suggest that you Google “Shirley Schwartz oil life monitor” for more on this.

Read this Mr. Bing and note that the program is said to be adjusted for a particular engine and is used as is or modified by others.

When you pull out the dipstick and can no longer read the markings on the stick because the oil is so dirty, you should have changed your oil yesterday, period. People who brag about getting 250-300K miles out of an engine, change their oil every 3000-5000 miles. For those on a 3 year lease, one oil change is enough during the lease… It’s all a matter of perspective…

Your obviously have high faith in the OLM, and your banking your $35,000 investment with it.

Me, I like cheap insurance.

I’m thinking about extending my oil changes but at the 3,000 miles that GMC lets me drive before the oil change due light comes on, that oil is ugly. It’s also five months old so I will probably change it in late April, since I just changed it. My annual tire pressure check may be due then too. Maybe not. The bold print on Yesterdays receipt says the tire place checks pressure at every visit! It’s a tire place, you gotta trust them.

To those who don’t agree with the owner’s manual or the onboard computer regarding oil change frequency:

Do you also disagree with the manual regarding oil type and weight, antifreeze type, transmission fluid? What can make people think that they are experts regarding oil change frequency lacking experience designing and testing engines or even having their oil tested? How about the aluminum alloy chosen for pistons. Is it good enough? Transmission gear hardness? Too soft or too hard for you? Do you have better light bulb types that should be used instead of those specified in the owner’s manual? I could go on.

Some will go to the trouble of verifying the effectiveness of onboard oil change computers. These computers have been around for a while now and if there was a problem you certainly would have heard about it by now.

My prediction is that one day, and you will see it here on Car Talk, onboard oil change computers will be commonly accepted. As is typical with anything new, there will be skeptics, especially something that takes judgment and control away from someone.

No one hear suggested the owner’s manual was wrong. The owner’s manual gives MIN IMUM requirements to maintain the engine. The oil and fluids I use exceeds the minimum requirements from Ford. The oil change interval I use is more frequent that the owner’s manual suggests, and way more frequent than the OLM suggests. Same with a lot of the maintenance the engine requires. Most manufacturers design these standards to make a reliable car through it’s service life, typically 6-7 years and 100,000 miles of normal use. I typically get better than 200,000 miles and more than 12 to 15 years of life out of them with mostly normal use.

I really don’t trust those OLMs, especially after the warranty runs out. I don’t trust that the meters take into account wear of the engine and the contamination rate that increases with age. With 191,000 miles on my truck, I’ll keep using my method, as it has never failed me.