Is it true that once you put synthetic oil in your car, you can never use regular again without a problem?

Thanks

 

Yes and no. But mostly no, it's not true.

You can typically switch between regular and synthetic oil (and even synthetic blends) without any problems in viscosity. What you might run into is slight leakage from older seals if you have a high-mileage/older engine.

The only time you can't switch is if the regular oil you're using has castor oil (not "Castrol") in it. However, I don't think anyone has used that type of oil in this country for decades, so you're probably good to go. Just check it out first.

As a side note, you do have to be careful with motorcycle oils, since they typically have special additives since the engine lube is often shared with the transmission lube.

 

Modern oils you can use either type or even mix them if you have to. The stuff about seals leaking is people in denial that all old cars are going to eventually leak oil in any case.

 

I agree with MK- leaky seals is a seperate issue - mixxing dino with synth or vise versa is OK. Old wives tale- like so many out there.