Synthetic oil performs better in extreme conditions. We’re talking about hot engines, cold starts, and extended drain intervals. The difference in performance between synthetic and conventional oil matters when you’re running a high-performance engine, towing heavy loads, or going for longer drain intervals.
What is conventional oil?
Conventional oil is refined crude with uneven molecules. It thickens in cold weather and thins out when hot, which limits protection at temperature extremes. This works fine for basic commuter cars under normal driving conditions. Modern conventional oils also contain additives to improve performance in harsher environments.
What is synthetic oil?
Synthetic oil is chemically engineered from refined petroleum to make its molecules uniform in size and structure. It flows better in cold starts and resists thinning at high temps. It is also better at resisting oxidation, which means less sludge and longer protection. A fully synthetic oil can cost twice as much as conventional (“regular”) oil.
Top motor oil brands like Mobil 1 and Liqui Moly offer their own lines of synthetic oil formulated to meet different performance standards and engine requirements.
Conventional Oil vs Synthetic Oil: What’s the Difference?
Synthetic and conventional oil differ in their molecular structure, performance, and longevity. A 2019 AAA study found synthetic oil outperformed conventional oil by 47 percent across physical, chemical, and performance tests.
| Feature | Conventional Oil | Synthetic Oil |
|---|---|---|
| Base Oil | Refined crude oil | Chemically engineered molecules |
| Molecular Structure | Varying shapes and sizes | Uniform size and structure |
| Viscosity Index | Low-thickness: changes dramatically with temperature | High-viscosity: stays stable across temperature ranges |
| Cold Flow | Thickens up; poor circulation in extreme cold | Flows immediately even down to -40°F |
| High-Temp Protection | Thins out and breaks down under heat | Stays thick; maintains film strength |
| Oxidation Resistance | Prone to oxidation and sludge buildup | Resists breakdown and deposit formation |
| Volatility | More evaporation when heated | Less oil loss to exhaust |
| Additive Requirements | Needs more viscosity modifiers | Requires fewer additives |
| Change Interval | 3,000 to 5,000 miles | 5,000 to 7,000+ miles (up to 25,000 for some) |
| Cost per Change | ~$38 (most economical) | ~$70 (2-4x more expensive) |
Does Your Car Need Synthetic or Conventional Oil?
Check your owner’s manual first. If the manufacturer requires synthetic oil, then that’s what you have to use. Most vehicles from 2019 and later require either synthetic or synthetic blend oil. Keep in mind: your car’s oil change interval is based on the type of oil it’s recommended to use.
Diesel engines, especially those built after 2007 with diesel particulate filters (DPFs) and emissions equipment, typically require synthetic or synthetic blend oil. If your manufacturer specifies it, that’s what you have to use.
Tighter tolerances, higher operating temps, and advanced emissions systems demand the cleaner-burning properties and superior protection that synthetic provides.
Older diesel engines like the 5.9 Cummins have their own specific oil requirements that you should follow carefully.
Go with full synthetic if:
- Your manufacturer requires it.
- You have a turbocharged engine.
- You drive in extreme heat or cold.
- You tow or haul heavy loads regularly.
- You want to maximize engine life.
Stick with conventional if:
- Your car specifically requires it.
- You drive a basic commuter vehicle under normal conditions.
- You don’t mind frequent oil changes.
- Lowest upfront cost is the priority.
The best motor oil brands these days use advanced additive packages and meet the latest API and ILSAC specifications for both conventional and synthetic formulations.
Myths and Mistakes About Synthetic Motor Oil
Ignoring manufacturer specs. If your car requires synthetic, use it. Running conventional oil voids your warranty and accelerates wear.
Jumping straight to extended drains on dirty engines. Run shorter intervals for the first one or two changes. This will give synthetic oil time to clean out sludge and deposits.
Not upgrading your filter. Extended drain intervals require a filter rated for the same lifespan.
Myth: You can’t switch between conventional and synthetic.
Fact: Modern synthetics are fully compatible with conventional oil, blends, and other synthetics.
Myth: Synthetic is “too slippery” for all engines.
Fact: Some race engine builders prefer conventional or blends for flat tappet or roller cam engines. This is specific to certain high-performance builds, not everyday engines.
Final Thoughts on Your Choice of Engine Oil
The bottom line is that synthetic delivers measurably better protection, especially in extreme conditions. You can stick to conventional oil if: your car manufacturer recommends conventional oil, the upfront cost of synthetic oil is a bit steep, and you don’t mind changing oils at regular intervals.
