Can I Mix Synthetic Blend and Full Synthetic?

If you’re low on oil and all you have is a different type than what’s in your engine, it’s natural to wonder if you can mix synthetic blend and full synthetic oil.

The short answer: yes, you can. But whether you should depends on a few important factors.

Mixing a synthetic blend (which is part conventional oil and part synthetic) with fully synthetic oil won’t damage your engine.

All motor oils on the market today (synthetic, blends, or conventional) are compatible with each other to meet API and SAE standards.

But here’s the catch:

• The performance of the oil in your engine will drop to the level of the lesser-quality oil in the mix.
• The benefits of full synthetic, like extended drain intervals, cleaner operation, and better wear protection, will be diluted.

So, yes, it’s safe in a pinch. But it’s not ideal as a long-term practice.

When is it Okay to Mix Them?

You might mix synthetic blend and full synthetic oil in cases like:

• Topping off between oil changes if you’re running low
• You’re on the road and only have access to one type
• You’re switching from synthetic blend to full synthetic and need to gradually transition

It’s fine to do this occasionally. But if your goal is maximum engine protection, it’s better to stick with one type, preferably fully synthetic.

Will Mixing Affect Oil Life or Performance?

Yes, it can. Mixing oil types may affect:

• Viscosity stability, especially under high heat or cold starts
• Oxidation resistance, meaning the oil may degrade faster
• Additive balance, since each formulation includes different detergents, dispersants, and anti-wear compounds

This can result in shorter drain intervals and slightly lower performance, especially if the blend is heavier on conventional oil.

Keep in mind, if you’re driving in cold Canadian winters or the high heat of southern U.S. highways, using a consistent, fully synthetic oil will better protect your engine in those extreme conditions.

My Experience Mixing Oil Types

Years ago, I used to mix whatever I had on hand. Sometimes it worked fine, other times I noticed the engine felt rougher or required more frequent changes.

Since switching to AMSOIL Signature Series, I’ve never looked back. It delivers such consistent performance and longevity that I no longer worry about mixing, topping off, or frequent oil changes. Plus, it runs clean and smooth, no matter the season.

If you’ve mixed oils once, no need to panic.

Just plan to:

• Change the oil a little sooner than usual
• Use a high-quality oil filter
• Next time, flush and replace with your preferred full synthetic to get back on track

If you want the benefits of full synthetic, it’s worth getting back to 100% synthetic as soon as possible.

Why AMSOIL Makes the Difference

AMSOIL’s fully synthetic oils are built using Group IV and V base oils, not just refined mineral oil labeled as “synthetic.”

That means they provide:

• Better oxidation stability
• Cleaner engines over time
• Superior performance in both cold starts and high-load driving
• True long-drain protection up to 20,000 miles or 1 year
• Proven lubrication efficiency and engine wear reduction
• Meets or exceeds API SP and ILSAC GF-6 standards for modern engine protection

Whether you’re maintaining a daily driver, a performance vehicle, or a fleet, AMSOIL gives you peace of mind with fewer oil changes and better engine health.

Explore AMSOIL Full Synthetic Options

Mixing a synthetic blend with full synthetic is safe, but not optimal.

It won’t damage your engine, but you’ll lose out on some of the protection, performance, and longevity that full synthetics offer.

If you’re aiming for the best possible care for your engine, fully synthetic oil is the way to go, and AMSOIL remains my top choice for consistent, reliable results.

Read more…

1. Difference Between Synthetic and Fully Synthetic Oil
2. Group III vs Group IV Explained Simply
3. Group IV vs Group V Base Oils: What’s the Difference?