Walk into a quick-lube shop and you will be offered a choice: conventional oil or synthetic, with a different price and often a different sticker for the next visit. It is easy to assume that paying more for synthetic buys you a longer wait. The research and the manufacturer rules say it is more subtle than that.
Short answer: use the oil grade and specification in your owner’s manual, and change it at the interval the manual (or the oil life monitor) gives. Synthetic oil protects better in tests, but AAA says it does not by itself stretch the interval.
What AAA actually found
In 2017 AAA compared conventional and full synthetic oils using eight industry laboratory tests. They covered things such as viscosity at high temperature, resistance to deposits, evaporation loss, pumpability in the cold and resistance to oxidation. Across those tests, AAA reported that synthetic oils did on average 47 percent better than conventional ones.
Two cautions help you read that number. First, it is an average of laboratory tests, not a measure of how many extra miles an engine will last. AAA’s fact sheet does not publish individual wear figures. Second, the study is from 2017, so treat it as one data point and not as the last word.
AAA’s practical conclusions were modest. Very few vehicles specifically require synthetic oil, and for most cars you can choose either type as long as it meets the specification in the manual. Conventional oil that meets the specification will not harm the engine.
Conventional vs synthetic at a glance
| Conventional | Synthetic | |
|---|---|---|
| Professional oil change (AAA 2017 average) | $38 | $70 |
| Five quarts, do it yourself (AAA 2017 average) | $28 | $45 |
| Lab test performance (AAA, 2017) | Baseline | 47% better on average |
| Required by the manual? | Often allowed | Required only for some vehicles |
| Longer change interval? | Follow the manual | Not automatically, follow the manual |
AAA put the extra cost of synthetic for an average driver at about $64 a year, or $5.33 a month, at 2017 prices. Whether that is worth it depends on how hard your engine works.
When synthetic is worth considering
AAA says the extra protection is most useful in a few situations:
- Newer vehicles with turbocharged engines
- Frequent stop-and-go driving
- Towing heavy loads
- Extreme weather, hot or cold
The Drive’s John Pearley Huffman makes a similar point from the other side. Synthetic oil is more stable under extreme conditions, but most cars never see conditions severe enough to make a difference. If the maker does not specify synthetic, he says conventional oil is fine when you use the correct grade, change it regularly and choose oil that carries the American Petroleum Institute seal. He also recalls a 1996 Consumer Reports test of 20 oils in New York taxis, where conventional oil protected as well as synthetic. That test used older, lower stress engines, so it does not settle the question for a modern turbo engine.
Can you switch from conventional to synthetic?
Yes, according to the sources we read. An Amsoil engineer, writing in an article supplied by the company, says it is safe to switch to synthetic at any time and that synthetic and conventional oils must meet the same minimum industry standards, including seal compatibility. Treat that as a manufacturer’s view and not as independent testing. The safer route is the same as always: use an oil that meets the specification in your manual, and ask the shop to confirm it.
How to pick your interval
- Open the owner’s manual. Find the oil grade, the specification and the change interval. Most manuals list miles and months, and the earlier of the two applies.
- Check for an oil life monitor. If your car has one, follow it, and reset it after every change.
- Look at the severe schedule. Short trips, towing and extreme temperatures often fall under the shorter severe service schedule.
- Choose the oil that meets the specification. Pay for synthetic if the manual requires it, or if your driving falls into the harder categories above.
- Write the change down. Date and odometer reading, every time.
Our guide on how often to change oil shows how the mileage and time limits work together, and the guide on oil change intervals for high-mileage cars covers older engines. In Badger, the maintenance schedule tracks the oil change by both miles and months, so you can see which limit is coming first whichever oil you chose.
Common questions
Does synthetic oil last longer between changes?
AAA says synthetic oil does not mean longer intervals. Follow the interval in the owner’s manual or the oil life monitor, and do not stretch it because you chose synthetic.
Is synthetic oil worth the extra money?
AAA put the extra cost at about $64 a year at 2017 prices and said it may be worth it if your budget allows, especially for towing, extreme temperatures or stop-and-go driving. If your manual allows conventional and your driving is ordinary, conventional that meets the specification will not harm the engine.
Do I have to use synthetic oil?
Only if your owner’s manual says so. AAA notes that very few vehicles specifically require it. Most manufacturers require an oil that meets a specification, and you can usually choose between conventional and synthetic.
Can I mix synthetic and conventional oil?
We did not find a source on mixing that we could confirm, so we will not give a rule. Ask your shop, and use an oil that meets the specification in your manual.
