I bought synthetic, meant to buy conventional. I really don’t wanna deal with the always long line at the return desk. Can I just use the synthetic even if I use conventional usually?

The engine is a 3mz-fe in a Toyota Sienna.

I hope so, 'cause I've done it. These days I only use synthetic.

Me too. No problems have resulted.

Yes.

You can switch back and forth with no harm. The only time I wouldn't is if you car specifies to use synthetic (obviously not the case here).

Great, thanks!

Synthetic is superior in every way, except for new engine break-in. I don't know why you'd want to go back to mineral oil.

Yes.

You can even mix synthetic and conventional oil.

Also do not mix the two. For example, don't add a quart of conventional oil to an engine full of synthetic or vice versa. Make sure you change the filter when you do the oil change.

Addition to original above post- I stand corrected. My post was based on incorrect information from many years ago. Mixing is now considered ok. Sorry!

This message has been edited. Last edited by: Gene Hillman,

quote:

Originally posted by thumperfbc:
I bought synthetic, meant to buy conventional. I really don’t wanna deal with the always long line at the return desk. Can I just use the synthetic even if I use conventional usually?

The engine is a 3mz-fe in a Toyota Sienna.

You are good Mike, no issues at all.

quote:

Originally posted by Gene Hillman:
Also do not mix the two. For example, don't add a quart of conventional oil to an engine full of synthetic or vice versa. Make sure you change the filter when you do the oil change.

Why?

They are both engine oil. No issue mixing them. The only issue would be your wasting money on the advantages of synthetic by adding conventional. Other than that it will do no damage to your engine.

quote:

Originally posted by comet24:

quote:

Originally posted by Gene Hillman:
Also do not mix the two. For example, don't add a quart of conventional oil to an engine full of synthetic or vice versa. Make sure you change the filter when you do the oil change.

Why?

They are both engine oil. No issue mixing them. The only issue would be your wasting money on the advantages of synthetic by adding conventional. Other than that it will do no damage to your engine.

Yeah why? Wouldn't that be the same as using syn blend?

quote:

Originally posted by Skins2881:

quote:

Originally posted by comet24:

quote:

Originally posted by Gene Hillman:
Also do not mix the two. For example, don't add a quart of conventional oil to an engine full of synthetic or vice versa. Make sure you change the filter when you do the oil change.

Why?

They are both engine oil. No issue mixing them. The only issue would be your wasting money on the advantages of synthetic by adding conventional. Other than that it will do no damage to your engine.

Yeah why? Wouldn't that be the same as using syn blend?

No. To make it the same you have to shake it vigorously while jumping on one foot, spinning counterclockwise, and singing It's Raining Men.

Trust me, I'm in oil & gas

Yes, it's interchangeable. Synthetic could cause leaking seals/gaskets to leak more while you're using synthetic on very high mileage vehicles. Other than that, it's generally superior to mineral oil in every way, but depending on your change interval might not benefit you at all.

You're fine. I've done it many times when I had my Toyota Tacoma. I used Mobil 1 synthetic and changed the oil at around 7K miles intervals.

After 4-5 changes of synthetic oil, I switched to Walmart Supertech conventional oil and ran for 1K miles to flush the engine, then back to Mobile synthetic again. Never experienced any leakage due to switching different oils.

When I sold my Toyota Tacoma it had 368K miles on the odometer and the engine still ran fine with no issues whatsoever. It also did not eat oil for an engine with such high mileage.

I will continue to do the same with all my current vehicles.

I agree with above, most of us don’t plan on mixing.

The only reason would be if whatever engine had requirements for oil that wasn’t met, synthetic, or the viscosity.

I would disagree actually with switching back and forth.

If you have been using conventional oil for a long time, and have higher mileage, and switch to synthetic, you may see leaks appear.

If you have been using synthetic oil for a long time, and have high mileage, and switch to conventional, I have had leaks STOP.

This is my experience. What are the long term affects of low mileage, swapping back and forth??? maybe marginal... BUT, I am sharing what I have experienced personally.

My daughters car, 2003 Camry, was adding lucas stop leak to the synthetic oil as it was loosing a fair amount. Switched to conventional, SAME weight, and leaks have all but stopped.

I personally would stay with synthetic at all times, unless you have high mileage and leaks, or are burning it, then go conventional and cheap:-)

^^^ one of the biggest oft-repeated myths about synthetic oils is that they cause oil leaks. https://www.tomorrowstechnicia...-old-engine-to-leak/

quote:

Originally posted by PowerSurge:
^^^ one of the biggest oft-repeated myths about synthetic oils is that they cause oil leaks. https://www.tomorrowstechnicia...-old-engine-to-leak/

Not repeating a myth intentionally, just relaying personal experience.

We had a 78 motor home, dry as a bone, thought we would do some good and used synthetic oil.... multiple leaks developed within 5oo miles.

Was a costly mistake, and one I won't do again regardless what the internet says.

quote:

Originally posted by PowerSurge:
^^^ one of the biggest oft-repeated myths about synthetic oils is that they cause oil leaks. https://www.tomorrowstechnicia...-old-engine-to-leak/

Cause a leak, NO. But if you already have one, which many high mileage engines do (usually a seep that most owners don't even notice), the synthetic will leak more. Also with old gaskets in 1990's cars that weren't formulated for them, such as the GM truck engines of that era, yes they will cause leaks with the type of rubber they initially used for gaskets......keep in mind I'm talking 1990's GM engines or older (and some others). These gaskets do NOT like the additives in Synthetic oil. While this is a possibility in some vehicles, switching back to conventional usually turns the leaks back to normal. Aside from my own personal experience with this when I used to turn wrenches, there are many articles that support it.

https://www.yourmechanic.com/a...ic-oil-in-older-cars

https://www.cenex.com/about/ce...ive-engine-oil-myths

https://www.bobistheoilguy.com...howflat&Number=46927