Switching to Synthetic Oil After 400k Miles – Is It Safe?

If you own an older vehicle, switching to synthetic oil might seem like a no-brainer. However, there are some misconceptions about synthetics and how they affect vehicles with high mileage.

Many people mistakenly assume that synthetics can cause issues with older engine seals. While this may be true in certain instances, modern synthetic oils are designed to eliminate such potential risks.

Overview of Synthetic Oil

Synthetic oil is a petroleum-based lubricant designed to provide engine protection and performance. Synthetic motor oil contains additives which helps to prevent corrosion and rust, reduce friction, and enhance fuel economy for your engine.

Synthetic oils utilize chemical engineering to produce molecules of uniform size and shape. Apart from that these oils contain fewer impurities and typically come with better additives that shield and clean your engine better.

Many of these additives also offer better oxidation resistance, helping prevent sludge, varnish and deposits from forming in your engine over time. This is especially beneficial if you operate your vehicle under extreme conditions such as racing, driving on the highway or towing heavy loads.

Synthetic motor oils come in a range of viscosities, so you can select one suitable for your vehicle and needs. We also appreciate the fact that synthetic oil typically lasts longer between changes than conventional oil – up to 15,000 miles depending on brand and owner’s manual recommendations.

Switching to Synthetic Oil After 400k Miles

Read Also: Switching to Synthetic Oil After 200k Miles 

Switching to Synthetic Oil After 400k Miles

Synthetic oil is a specially engineered lubricant created in the lab. It utilizes additives to extend its shelf life beyond that of regular oil, offering superior engine protection.

Many modern vehicles already come with synthetic oil installed, making it an attractive option for drivers looking to maximize their car’s performance. But there are some important things you should be aware of before making the switch.

Engines typically tolerate up to 400k miles of synthetic oil before showing signs of wear. This is especially true for engines designed for high temperatures, like turbochargers and superchargers.

Though some may worry that switching to synthetic oil will result in leaks, this is not necessarily the case. Synthetic oil is much thinner than conventional oil, allowing for easier flow throughout your system.

Synthetic oils offer significantly longer service than conventional oil, and some even boast extended drain intervals up to 10,000 miles. If you’re considering switching over to synthetic oil, speak with your technician and consult the owner’s manual for more details.

Is It Safe to Switch to Synthetic Oil?

Many people worry that switching to synthetic oil for older vehicles could be hazardous, particularly because a full synthetic oil may not be compatible with engine seals and cause leaks.

Synthetic oils are thicker than conventional oils, keeping engine parts lubricated longer. Let’s not forget that synthetic oils contain additives to protect against corrosion, rust and other effects caused by engine wear.

However, these additives alone will not guarantee engine protection; thus it’s essential that your car receives regular maintenance and is in top working order before switching over to synthetic oil.

If you choose to switch from standard synthetic oil, it is wise to consult your owner’s manual for recommended oil change intervals. On average, standard synthetics should provide between 5,000-7,000 miles between changes.

If you can’t justify investing in a full synthetic oil change, consider purchasing a semi-synthetic blend or rotating between full and non-full synthetic every other oil change. Doing this will extend your oil change intervals while saving money over time.


If your car is older or has seen heavy use, then synthetic oil may be beneficial. Not only will synthetic motor oil extend engine life but it reduces sludge and friction within the engine compartment.

Synthetic oil is specially formulated with additives to clean and protect your engine, prolonging between oil changes. Furthermore, synthetic oil may improve fuel economy.

For your engine, the ideal synthetic oil should be one that contains high-grade additives and provides strong sludge and deposit protection at an affordable price. You’ll have no difficulty finding these oils.

Some vehicles do not respond well to synthetic oil, particularly older engines that have been around a while. They may not be able to handle the increased flow rate required by synthetic oil.