Can you switch back to conventional oil after using synthetic

Q: Can I switch from synthetic oil to regular oil? I read it's a myth, but my mechanic says you can’t. By the way, I still read your column here after I moved to Venice, Florida.

Table of Contents Show

Can you switch back after using synthetic oil?
Can you switch from full synthetic to conventional?
Is it bad to switch back and forth between synthetic oil?
What happens if I put conventional oil instead of synthetic?

A: Synthetic oil and regular oil, for the most part, use very similar base stocks.

Synthetic oil varies from conventional oil in the way that it is refined. The molecules in synthetic oil are very uniform, while in conventional oil the molecules vary in size. This is one of the reasons synthetic oil flows more quicker and remains cooler than conventional oil.

Yes, you can switch back and forth with no harm, although, in my opinion, the benefits of synthetic oil outweigh the costs of a conventional oil change.

Q: I am about to purchase a car — maybe not brand new but probably a couple of years old.

I have a 2010 Toyota Camry and have been very happy with it and want to get the same. What are the benefits of buying from a Toyota dealer? I do see some great deals from other dealerships that are not Toyota dealers.

A: When buying a used car from a new car dealer that sells the same brand of car, in many cases you are getting a “fresh” trade-in. Also, franchised car dealers will have exclusive access to factory auctions.

These recent trade-ins or manufacturer auction vehicles may have lower mileage, may be one-owner vehicles, and may have better overall history.

This doesn’t mean that other new and independent (large and small) dealers don’t have good cars. In fact, some car dealers will extensively recondition a used car — in some cases replacing the tires and batteries — to give that used car a new-car feel.

With any used car, it is always best to have it evaluated by a skilled technician prior to purchase.

Q: Our 2013 Ford Taurus key fobs are not locking and unlocking the car doors in a regular fashion. The car was a used car bought from a dealership, and the warranty expired in 2019.

Do I need to get the work done at a Ford dealership, or could any repair shop fix the problem? I am not sure whether the fobs, the unlocking receiver or the actual car locks are the problem.

A: Many auto parts stores have a simple device that can check to see if the key fob is transmitting, which will help verify the operation of the fob.

If the fobs are only working intermittently, a very common issue is that the battery becomes loose and loses the connection. In fact, Ford produced a new gasket/shim for the fob that solves this problem.

If the fobs are transmitting, then the issue is with the receiver. Any competent repair shop would be able to diagnose and handle the repair. I have found that the franchised dealer, or an automotive locksmith, are more familiar with these issues.

Q: I brought my Infiniti Q50 — with 50,000 miles — in to my local dealer for an oil change and alignment. They recommended four other services: transmission fluid change, power steering fluid change, throttle body cleaning and differential fluid change. I decided to go with the transmission fluid change but declined the rest, as none are listed on the service manual and they cost an additional $900.

When would the services I declined be necessary? I have trouble going with expensive services deemed necessary by the dealership that are not in the manual.

A: All of these fluid changes are only required if the fluid has started to deteriorate. As a general rule, according to Infiniti, power steering, transmission and differential fluids are a lifetime fill and, although they should be checked, there is no recommended replacement.

The throttle body cleaning is similar. If the vehicle has a cold-weather hesitation, it could be the result of carbon buildup in the throttle body, which is remedied by cleaning.

It doesn’t hurt to replace these fluids but, in most cases, it is not necessary.

John Paul is the AAA Northeast Car Doctor. He has more than 40 years of experience in the automobile industry and is an ASE-Certified Master Technician. Write to John Paul, The Car Doctor, at 110 Royal Little Drive, Providence, RI 02904. Or email and put “Car Doctor” in the subject field. Follow him on Twitter @johnfpaul or on Facebook.

Can you switch back after using synthetic oil?

Myth: Once you switch to synthetic oil, you can never switch back. This is one of the most persistent myths about synthetic oil—and completely untrue. You can switch back and forth at any time. In fact, synthetic blends are simply a mixture of synthetic and conventional oils.

Can you switch from full synthetic to conventional?

Yes! Switching from synthetic oil to conventional (and back again) won't cause any harm to your engine. Synthetic, synthetic blend and conventional oils are all compatible. In fact, that's what a synthetic blend is—a mix of synthetic and conventional oil.

Is it bad to switch back and forth between synthetic oil?

When it comes to doing oil changes, switching between synthetic and conventional oil is perfectly okay. Despite the oil myths, both oil types are compatible with each other – no engine flush needed. So, simply making the switch will not cause any damage to your engine nor impact your travels.