Longer oil change intervals with synthetic oil? The truth

Can you go longer between oil changes with synthetic oil?

Maintaining a vehicle involves a routine schedule of upkeep tasks to ensure optimal performance and longevity. Among these tasks, regular oil changes stand as one of the most critical. Traditionally, the recommended interval for oil changes with conventional oil has hovered around every 3,000 miles (4,800 kilometers). However, with the advent and increasing popularity of synthetic oil, many vehicle owners and experts alike have questioned whether these intervals can be extended. This article delves into the intricacies of synthetic oil and examines whether you can it truly go longer between oil changes if you switch to synthetic oil.

Think you can automatically extend oil change intervals simply by switching to synthetic? Think again. Read this latest Toyota service bulletin

In most cases, you can go longer between oil changes, but only by a little

In theory, synthetic oil should allow you to go longer between oil changes. But there’s no way to double or triple the length. You don’t know how long the oil will last in your engine without performing frequent oil analysis tests. You can’t extrapolate that data farther out than 20,000 miles. The bottom line is that oil life depends on many factors, and the differences between conventional and synthetic oil are just one of them.

Read on to learn more

Synthetic oil has many benefits

• Enhanced Stability and Performance— One of the primary benefits of synthetic oil is its superior thermal stability. Unlike conventional oil, which can break down or lose viscosity under extreme temperatures, synthetic oil maintains its performance. This stability is crucial in preventing engine wear and maintaining efficient operation over time.
• Better Lubrication—Synthetic oil’s uniform molecular size ensures smoother operation, reducing friction between engine parts. This reduced friction enhances performance and minimizes wear and tear, potentially extending the engine’s lifespan.
• Resistance to Breakdown— Synthetic oil is more resistant to oxidation and thermal breakdown. Conventional oils can form sludge or varnish deposits over time, leading to potential engine blockages. Synthetic oils, however, remain cleaner and maintain their protective qualities for longer periods.
• Improved Fuel Efficiency—Synthetic oil’s superior lubricating properties can improve engine efficiency, leading to better fuel economy. This improvement, albeit sometimes marginal, can be a significant advantage over the long term.

However, that doesn’t automatically mean you can extend your oil change intervals

Given these advantages, it’s reasonable to consider extending oil change intervals when using synthetic oil. Many automotive manufacturers and oil companies have recognized this potential, often recommending oil change intervals between 7,500 to 10,000 miles (12,000 to 16,000 kilometers) or even longer for vehicles using synthetic oil.

Oil life is dependent on other factors that most drivers don’t understand

The Service Category Matters— The way you drive affects oil life

Your owner’s maintenance guide lists recommended oil change intervals for normal and severe service. Most city dwellers fall into the severe service category but maintain their vehicles according to the normal service category.

The exact definition of severe driving service varies by carmaker, but generally severe service is defined as:

• Short trips— Less than 10 miles in cold weather or 5 miles in warm weather. Short trips dramatically reduce the life of your oil due to start-up contamination. Start-ups introduce unburned fuel, moisture, and soot into the crankcase, and the oil doesn’t get hot enough to evaporate off or filter out those contaminants. The contaminants form sludge and acids that more rapidly deplete the protective additives in your oil, even if you use synthetic oil.
• Driving in extremely hot, cold, or dusty climates— Your engine doesn’t perform as efficiently in these conditions, and that inefficiency shows up in faster oil degradation
• Sustained stop-and-go driving— Stop-and-go traffic causes multiple periods of acceleration and deceleration where the engine air/fuel management system can’t run efficiently. The frequent stops and extended idling causes the oil to run at higher temperatures, resulting in accelerated oxidation and thermal breakdown.
• Extended idling— Idling reduces the oil’s ability to dissipate heat, causing additional oxidation and breakdown.
• Carrying heavy loads or towing a trailer— Loading the engine causes more oil shear, reducing the oil’s viscosity and depleting the supply of viscosity index improvers.

Engine design and your engine’s condition affect oil life

Older engines don’t run as efficiently as late-model engines. So they tend to contaminate the oil more than newer engines. Changing to a synthetic oil doesn’t reduce the contamination rate because that’s dependent on the engine design, something you can’t change.

In other words, depending on their condition, older vehicles or those with high mileage might still require more frequent changes.

How you maintain your vehicle also determines oil change intervals

All carmakers recommend checking your oil

This image shows a stuck oil control ring on an engine with 150,000 miles. The owner changed the oil every 10,000 miles, but the engine had to be replaced because it burned a quart of oil every 500 miles due to stuck oil control rings.

level regularly and topping off with the recommended oil. Most drivers never check their oil between oil changes. Yet, all engines burn some amount of oil. The oil burning was less noticeable when everyone changed their oil every 3,000 miles. However, when you boost the oil change interval to 7,500 or even 10,000 miles, the loss of oil is noticeable.

Shops routinely report that cars that come in for oil changes are often 1 to 2 quarts low. Driving with a low oil level dramatically reduces the life of the remaining oil by 25% or more. Think about that!

If you change your oil every 10,000 miles but don’t check the top it off when it’s a quart low, you’ve effectively worn out your oil at 7,500 miles. That means you’ve been driving on depleted oil for 2,500 miles.

Other things to consider before you risk longer oil change intervals with synthetic oil

• The oil filter has to work the entire time— If you switch to synthetic oil, but don’t also switch to a more expensive long-life oil filter rated for the same number of miles, you’ll defeat the purpose of switching.

• You have no way to judge how long to extend the oil changes— Yes, you can perform several oil analysis tests, and those tests can tell you the viscosity of the oil and the presence of wear metals, such as iron, copper or tin, giving you an indication of engine wear. However, those tests can’t tell you how much varnish or sludge has accumulated in your engine.

For other oil-related posts, click here

For an updated post on engine oil life, read this

© 2015 Rick Muscoplat