What happens if I put 5W-30 instead of 5W 20 in my car?
In short, whether you can use 5W-30 depends on your car’s manual. If the manufacturer allows a range that includes 5W-30, it’s generally acceptable; otherwise, it can affect fuel economy, engine wear under certain conditions, or warranty coverage. This article explains what the numbers mean and how the change might play out in practice.
Understanding what the numbers mean
Oil viscosity grades are a shorthand for how the oil behaves when the engine is cold and when it’s hot. The first number, followed by the W, indicates cold-start performance (the lower the number, the better the oil flows when cold). The second number indicates high-temperature viscosity, or how thick the oil remains when the engine is up to operating temperature. Between 5W-20 and 5W-30, the winter (cold-start) rating is the same, but 5W-30 is thicker at running temperature.
At-a-glance differences
- Cold-start behavior: both grades with 5W flow similarly in cold conditions due to the same 5W rating.
- High-temperature viscosity: 5W-30 stays thicker when the engine is hot, offering more film strength and potential protection under high heat or heavy loads.
- Fuel economy: engines “designed for” 5W-20 may see a small fuel-economy difference with 5W-30; the effect varies by engine and driving style.
- Engine tolerances and seals: some engines are tuned for a specific grade; using a different grade can affect oil clearance, seals, and leaks if outside the manufacturer’s spec.
Bottom line: the practical impact hinges on whether your car’s manufacturer approves using 5W-30 in place of 5W-20 and on operating conditions such as climate and driving loads.
Practical implications for your car
If your vehicle manual does not strictly require 5W-20 only, switching to 5W-30 can have mixed results depending on the engine design and climate.
- Potentially better protection in hot weather or under heavy loads due to a thicker oil film.
- A possible slight decrease in fuel economy and possibly more engine drag due to higher viscosity.
- Risk of oil-starved lubrication or higher oil pressure in engines calibrated for thinner oil, which can stress seals or gaskets.
- Minimal difference in cold-start performance since both grades share the same winter rating, but extreme cold areas might prefer a lower high-temperature grade.
- Warranty and manufacturer compliance: using a non-specified grade could complicate warranty claims if damage is attributed to oil viscosity outside the recommended range.
Many modern cars specify a viscosity range (for example, 5W-20 to 5W-30) that is acceptable or even recommended under certain conditions. Always check your owner’s manual or manufacturer guidance before deviating from the exact grade.
What to do if you already used 5W-30
If you’ve already poured 5W-30 into an engine that specifies 5W-20, take these steps to minimize risk and keep your engine healthy.
- Consult the owner's manual or manufacturer’s technical notes to confirm whether the 5W-30 is within the acceptable range for your engine.
- Ensure the oil meets the required specifications (certifications and additive packages), not just the viscosity.
- At the next scheduled oil change, consider returning to the recommended grade if 5W-20 is specified, especially if you notice any unusual symptoms.
- Monitor for signs of trouble: unusual noises, increased oil consumption, oil leaks, or a malfunctioning oil pressure warning light.
- Keep documentation of the oil used (brand and grade) for service records and potential warranty considerations.
In many cases, using 5W-30 temporarily in a vehicle that can tolerate it is unlikely to cause immediate harm, but it’s prudent to revert to the manufacturer-recommended grade as soon as possible.
When to avoid using 5W-30
There are clear situations where 5W-30 should not be used in place of 5W-20 or another specified grade.
- When the manufacturer specifies a narrow viscosity grade that does not include 5W-30, particularly for modern engines designed for maximum fuel efficiency.
- In engines with tight tolerances, advanced emissions systems, or hydraulic systems calibrated for a specific oil viscosity.
- If warranty coverage depends on using the exact viscosity and specification, deviating could complicate claims.
- In very cold climates, where a lower cold-start viscosity (such as 0W or 5W) might be preferred for easier starts and quicker lubrication.
When in doubt, contact the vehicle manufacturer, a dealership service department, or a trusted mechanic to confirm compatibility before continuing to use 5W-30 long-term.
Summary
The compatibility of using 5W-30 instead of 5W-20 hinges on your car’s design and the manufacturer’s specifications. If your manual allows a range that includes 5W-30, the change may be acceptable and could offer better high-temperature protection in hot climates, with a potential trade-off in fuel economy. If the manual specifies 5W-20 only, sticking with the recommended grade is the safer course to protect engine health and maintain warranty coverage. When in doubt, revert to the prescribed grade at the next opportunity and consult a professional for guidance tailored to your vehicle.
