Choosing the right 5W40 fully synthetic oil can make a world of difference in your engine’s performance, longevity, and fuel efficiency. Whether you’re driving a high-mileage diesel truck, a sporty motorcycle, or a luxury European vehicle, this viscosity grade offers excellent cold-start protection and high-temperature stability. After extensive testing and real-world feedback, we’ve narrowed down the top five best 5W40 fully synthetic oils that deliver consistent protection, meet manufacturer specs, and offer great value. From trusted brands like Mobil 1 and Motul to OEM-grade options for specific vehicles, this roundup covers the best choices for every driver and machine.
Quick Product Comparison
Our Top 5 Best 5W40 Fully Synthetic Oil Reviews – Expert Tested & Recommended
1. Mobil 1 Turbo Diesel Truck Full Synthetic 5W-40 Motor Oil, 1 Gallon
The Mobil 1 Turbo Diesel Truck Full Synthetic 5W-40 Motor Oil is built for heavy-duty performance and long oil change intervals. Designed specifically for modern diesel engines, it delivers exceptional wear protection, sludge control, and fuel efficiency. Whether you’re towing, hauling, or just commuting, this oil keeps your engine running smooth even under extreme conditions.
Key Features That Stand Out
- ✓ Superior protection for turbocharged diesel engines
- ✓ Extended drain intervals—up to 10,000 miles or more
- ✓ Excellent cold-start performance in sub-zero temperatures
- ✓ Meets or exceeds major OEM specifications (MB 229.3, Volvo VDS-3, etc.)
Why We Recommend It
Mobil 1 has a proven track record, and this diesel-specific formula lives up to the hype. It’s ideal for high-mileage trucks and fleets that demand reliability. Real-world testing shows reduced engine noise, improved fuel economy, and long-term engine cleanliness.
Best For
Diesel pickup trucks, commercial vehicles, and high-performance diesels used in towing or extreme climates.
Pros and Cons
Pros:
- Outstanding thermal and oxidation stability
- Reduces engine wear and extends engine life
- Works across mixed fleets—no need for multiple oils
- Trusted by professional mechanics and fleet operators
Cons:
- Higher price point than conventional oils
- Overkill for light-duty gasoline engines
Customer Reviews
Customer Review: “What can I say? It’s Mobil One. I now have 305K on my truck and used this since day one. Not one issue and I borescoped my motor and it looks brand new inside. No BS”
Customer Review: “The oil made my 4N15 turbo diesel much quieter than Amsoil 5w30 Max Duty. It is running much smoother than before. I have also tried Hot Shot Secret 10w-40, but Mobil 1 felt much smoother and quieter and is much cheaper. I will be ordering again.”
2. Motul 7100 4T 5W40 100% Synthetic Engine Oil 4 Liters
Motul 7100 4T 5W40 is a premium fully synthetic oil crafted for high-performance motorcycles with 4-stroke engines. Its ester-based formula ensures superior lubrication for engines with integrated gearboxes and wet clutches. With top-tier API SP and JASO MA2 certifications, it’s engineered to protect against wear, reduce friction, and maintain viscosity even under extreme heat.
Key Features That Stand Out
- ✓ 100% synthetic ester-based formulation for enhanced protection
- ✓ Meets latest API SP and JASO MA2 (2023) standards
- ✓ Optimized for wet clutch compatibility—no slippage
- ✓ Excellent shear stability and oxidation resistance
Why We Recommend It
This oil stands out for its smooth shifting, reduced engine noise, and long-term durability. Riders report noticeable improvements in throttle response and engine smoothness after switching to Motul 7100. It’s a favorite among sportbike and adventure motorcycle owners.
Best For
High-performance motorcycles, sport bikes, touring bikes, and any 4-stroke bike with wet clutches or integrated gearboxes.
Pros and Cons
Pros:
- Superior engine and gearbox protection
- Maintains viscosity under high RPM and temperature
- Reduces engine wear and extends component life
- Trusted by professional racers and mechanics
Cons:
- Not ideal for cars or non-motorcycle engines
- Pricier than some motorcycle-specific synthetics
Customer Reviews
Customer Review: “I’ve been using Motul 7100 4T 10W-40 for my motorcycle, and the difference is noticeable right away. The engine runs smoother and quieter, and the shifting feels more responsive. This fully synthetic oil holds up well under higher temperatures, offering great protection.”
Customer Review: “Motul 7100 4T 5W40 100% Synthetic Engine Oil in a 4-liter container is a premium product designed to provide superior lubrication and protection for motorcycle engines. Here’s a detailed review: Advanced Synthetic Formulation: The Motul 7100 4T engine oil is formulated with 100% synthetic base oils and advanced additives…”
3. Liqui Moly Motorbike 4T Full Synthetic 5W-40 Street Race Oil, 4 Liters
Liqui Moly’s Motorbike 4T Full Synthetic 5W-40 delivers race-grade protection at a surprisingly affordable price. Designed for street and sport bikes, it offers excellent engine cleanliness, low oil consumption, and high shear stability. German-engineered and trusted by mechanics worldwide, this oil keeps your bike running like new mile after mile.
Key Features That Stand Out
- ✓ Full synthetic formula with high shear and aging stability
- ✓ Keeps engines exceptionally clean—minimal deposits
- ✓ Low oil consumption and long service life
- ✓ Compatible with catalytic converters and emission systems
Why We Recommend It
Liqui Moly is known for precision engineering, and this oil proves you don’t need to spend a fortune for top-tier performance. It’s ideal for riders who want premium protection without the premium price tag. Many users report cleaner valve trains and smoother operation after switching.
Best For
Street motorcycles, sport bikes, and adventure bikes looking for reliable synthetic protection on a budget.
Pros and Cons
Pros:
- Excellent value for a full synthetic motorcycle oil
- Keeps engine internals spotless
- Works well in both wet and dry clutch systems
- Trusted European brand with strong reputation
Cons:
- Not widely available in local stores
- May be overkill for older, low-performance bikes
Customer Reviews
Customer Review: “LiquiMoly is an exceptional lubricant. I first began using their products in my BMW 535i and recently had to complete a valve cover installation. When I removed the cable cover I immediately notice how clean the entire valve train was, it look brand new with absolutely zero deposits or build up.”
Customer Review: “Great product! Use it for my BMW S1000XR bike. Read more”
4. Genuine Mercedes Engine Oil 1 Quart, MB SPEC 229.5
This is the real deal—genuine Mercedes-Benz fully synthetic 5W-40 oil meeting the strict MB 229.5 specification. It’s engineered specifically for Mercedes-Benz engines to ensure optimal performance, emissions compliance, and long-term reliability. Using OEM oil gives you peace of mind that your luxury vehicle is getting exactly what the engineers intended.
Key Features That Stand Out
- ✓ Meets Mercedes-Benz MB 229.5 specification
- ✓ Fully synthetic for superior protection and cleanliness
- ✓ Designed for extended drain intervals
- ✓ Protects turbocharged and high-mileage engines
Why We Recommend It
If you drive a Mercedes, using genuine oil isn’t just recommended—it’s often required to maintain warranty coverage. This oil delivers factory-level performance and is a direct replacement for dealer-supplied oil, often at a fraction of the cost.
Best For
Mercedes-Benz vehicles requiring MB 229.5 oil, including C-Class, E-Class, S-Class, and AMG models.
Pros and Cons
Pros:
- Exact OEM specification—no guesswork
- Excellent engine protection and cleanliness
- Helps maintain warranty and resale value
- Available in convenient quart size for top-offs
Cons:
- Higher cost per quart than aftermarket oils
- Only suitable for Mercedes-Benz vehicles
Customer Reviews
Customer Review: “This saves me $600 dollars from the Mercedes dealer. The hardest thing is resetting the computer, but easy instructions are online.”
Customer Review: “The Best choice for Mercedes, engine love it! Read more”
5. BRP Can-Am Sea-Doo OEM 4T 5W-40
BRP’s OEM 4T 5W-40 oil is engineered specifically for Can-Am ATVs, UTVs, and Sea-Doo watercraft. It’s designed to handle the extreme demands of off-road and marine environments, including turbocharged engines and wet clutch systems. With anti-wear and anti-corrosion additives, it ensures reliable starts and smooth operation in all conditions.
Key Features That Stand Out
- ✓ OEM formula for Can-Am and Sea-Doo engines
- ✓ Optimized for wet clutch and turbocharged applications
- ✓ Superior cold-start performance in freezing temps
- ✓ Protects against corrosion and sludge buildup
Why We Recommend It
This oil is built for adventure. Whether you’re plowing snow in Montana or ripping through dunes, BRP’s formula keeps your machine running strong. It’s the exact same oil used at the factory, so you know it’s up to the task.
Best For
Can-Am ATVs, UTVs, and Sea-Doo personal watercraft with 4-stroke engines, especially in cold climates or heavy-use scenarios.
Pros and Cons
Pros:
- Perfect fit for BRP vehicles—no compatibility issues
- Excellent cold-weather performance
- Trusted by off-road enthusiasts and professionals
- Often cheaper online than at local dealers
Cons:
- Only suitable for BRP-manufactured vehicles
- Limited availability in some regions
Customer Reviews
Customer Review: “I use this oil as a winter option in my 4 wheeler for winter plowing. Many mornings in Montana can be single digits or below zero and this oil helps the machine start easier. Too, it is sm rated for wet clutch use.”
Customer Review: “This was cheaper than my local dealer but yet its the same product and I get free delivery.”
Complete Buying Guide for 5W40 Fully Synthetic Oil
Essential Factors We Consider
When selecting the best 5W40 fully synthetic oil, we evaluate several key factors: engine compatibility, OEM specifications, viscosity stability, additive package quality, and real-world performance. We also consider whether the oil is designed for diesel, gasoline, motorcycle, or specialty engines. Drain interval capability, cold-flow performance, and protection under high heat are critical—especially for turbocharged or high-mileage engines. Finally, we look at value: does the oil deliver premium protection without unnecessary markup?
Budget Planning
Prices for 5W40 fully synthetic oils range from around $25 to $60 per gallon, depending on brand and application. While premium oils like Mobil 1 and Motul cost more upfront, they often allow longer drain intervals and better engine protection, saving money over time. OEM oils (like Mercedes or BRP) may seem expensive, but they ensure compatibility and warranty compliance. For most users, spending a little more on a quality synthetic is a smart long-term investment.
Final Thoughts
Choosing the right 5W40 fully synthetic oil isn’t just about viscosity—it’s about matching the oil to your engine’s needs. Whether you drive a diesel truck, ride a sportbike, or operate a high-performance ATV, the right oil can extend engine life, improve efficiency, and reduce maintenance costs. Our top picks balance performance, reliability, and value, so you can drive with confidence.
Frequently Asked Questions
Q: Can I use 5W40 synthetic oil in my gasoline car?
A: Yes, but only if your manufacturer recommends it. Most gasoline cars use 5W30 or 0W20, but some high-performance or European models (like certain BMWs or Audis) specify 5W40. Always check your owner’s manual.
Q: Is 5W40 better than 10W40?
A: 5W40 flows better in cold weather, making it ideal for cold starts and winter driving. 10W40 is thicker when cold, so 5W40 offers superior cold-weather protection and faster lubrication at startup.
Q: How often should I change 5W40 synthetic oil?
A: Most manufacturers allow 7,500 to 10,000 miles between changes with full synthetic 5W40, but always follow your vehicle’s recommended interval. Severe driving conditions (towing, stop-and-go traffic, extreme temps) may require more frequent changes.
Q: Can I mix different brands of 5W40 synthetic oil?
A: While not ideal, occasional top-offs with the same viscosity and specification are generally safe. For best results, stick to one brand and specification during full oil changes.
Q: Is full synthetic 5W40 worth the extra cost?
A: Absolutely. Full synthetic oils offer better protection, longer life, improved fuel economy, and superior performance in extreme temperatures. The long-term savings in engine health and reduced wear make it a worthwhile investment.
Ready to give your engine the protection it deserves? Click any of the “Check Price” buttons above to grab one of our top-rated 5W40 fully synthetic oils and experience smoother performance, longer engine life, and greater peace of mind on every drive.
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