Switching To Synthetic Oil After 200k Miles [The Myth & Truth]

You may run a 2010 Honda Accord or 1996 850 Turbo, and it’s got about 200K miles with 30% of oil life on the oil life indicator. Last 10000 miles, you used high mileage conventional oil into it. Now, you want to switch to synthetic oil to maximize fuel economy and engine life. But you heard switching can cause leaks. So, this question comes into your mind naturally switching to synthetic oil after 200K miles.

Well, it all depends on the engine conditions. If the engine seals are good,  you can switch to synthetic without thinking twice. However, modern synthetic oil doesn’t include the additives that cause a leak on the old cars. To get more insight, continue to read. 

Switching To Synthetic Oil After 200k Miles [The Myth & Truth]

Experts are against switching to synthetic oil in older or high mileage cars. The seals, gaskets, and other components in a high mileage car get worn out or are not tight compared to the newer models. As the synthetic oil cleans out sludge from the engine, it may remove the sludge that acts as a seal. Consequently, it will cause leaks and be responsible for burning oil. If you don’t check the oil level often, it will surely damage the engine. 

However, it doesn’t mean you can’t put synthetic oil into your high mileage car (over 200k miles). If the engine seals are in good condition and have no mechanical problems, you can switch to synthetic oil. Switching to synthetic oil will provide better lubrication and offer more stability in cold temperatures. Some synthetic oils like Mobil 1 High Mileage are specially formulated for high mileage cars. 

Before putting synthetic oil in, we recommend you clean the seals first. Otherwise, there will develop significant leaks, which are evidence of the deposit buildups. So, use a crankcase cleaner like ARX to clean the deposits. Then, address other gasket leaks and fix them. Now, you can change the oil with much higher confidence. 

In short, you can switch to synthetic oil if the engine seals and gaskets are in good condition. Otherwise, it will damage the engine components. Alternatively, you can stick with the existing oil you put into the engine as it supports you well for the last 200k miles. 

Note: You can also read Is switching to Synthetic Oil after 100k miles.

Can You Switch To Synthetic Oil With High Mileage

It all depends on your engine condition. If your engine is in good condition and there is no leak, you can go ahead and make a change with synthetic. On the other hand, we don’t recommend you put synthetic oil into your engine if your engine is losing or burning oil. 

Switching to synthetic oil will pose no trouble at any mileage as long as the engine internals are intact or well. Synthetic oil is better in removing sludge buildups. It also improves engine performance by enhancing mileage. 

However, you should clean the seals using ARX if you have older or high-mileage cars. Then, fix the leaks and put synthetic oil to get the most out of it. 

Is It Ok To Switch From Conventional To Synthetic Oil?

Yes, it’s ok to switch from conventional to synthetic oil, and it doesn’t pose any damage to the engine. Both synthetic and conventional oil are compatible with each other though there is a lot of myth. 

Conventional oil has unstable chemical structures as it uses crude oil as its built-in ingredients. Because of it, this oil breaks down quickly and sacrifices the engine protection quality. 

On the other hand, the chemical structures of synthetic oil are stable and stay longer in the engine. So, it provides superior engine protection by lubricating every moving component of your car engine. 


How many miles should you change your synthetic oil?

It actually depends on your vehicle and the synthetic oil brand you put. However, it is recommended to make an oil change every 7500-15000 miles. We recommend you check out the car manual and maintain the oil change interval it suggests. 

Can synthetic oil last 15000 miles? 

Yes, synthetic oil may last for 15000 miles. However, we don’t recommend you to do so as it will void the warranty and may bring damage to your engine. Follow the manufacturer’s guidelines and do the oil change according to the manual. 

Is synthetic oil good for old cars?

Yes, it’s good for old cars until the internal components are intact. The synthetic oil stays longer, lubricates every moving part well, and performs the best. And the best part is- that modern synthetic oil doesn’t include the additive that causes damage to your old car. 

Can high mileage oil damage an engine?

No, high mileage oil doesn’t pose any damage to the engine and it will prevent leaks. 

Should you use thicker oil with high mileage cars?

Yes, you should use thicker oil with high mileage cars as it lasts longer in the engine and ensures superior lubrication & protection. 


Keep in mind; it’s a myth that synthetic oil causes leaks on old cars. It means you can switch to synthetic oil without any hesitation as it will extend the engine life. 

However, it will be best to check all the oil seals and gaskets are in good condition before making a change-over. Just use ARX (a crankcase cleaner) to clean the seals to remove deposits buildup. Then, fix the leaks and you are ready now to put synthetic oil into your high mileage cars.

About John M

John contributed as a technical head at an automobile company just 2 years after his post-graduation in Automobile Engineering. He loves to lead a free life, so he left his job & started blogging. Now, he does research on every automotive problem, part & product and seeks a better solution & best products & shares his findings with his readers to help them as well as to minimize their struggle.

Leave a Comment