I have a Toyota Corolla. Since I bought it brand new a few years ago, I always have gotten synthetic oil on the oil changes. I have always used the Toyota dealership.

When I got the oil changed yesterday, they accidentally used the normal oil instead of the synthetic oil. I found this out by look at the itemized receipt.

The advisor said that I can bring the car in and they will switch out the oil and filter for the synthetic oil and new filter.

The problem is... how will I know they will do that? There is no way to verify since the oil is already clean looking on the dipstick. They could easily just let my car sit for 20 minutes and give it back to me.

I really want synthetic oil in my car. It's my investment and it gives me a peace of mind.

What should I do in this situation?

  • take a sharpie or something and make a mark on the filter, at least you will know if they replaced that.
    – agentp
    Jan 10, 2018 at 17:30
  • Synthetic oil is generally considered better than conventional oil and has a higher change interval. If you want to be sure you get the right oil/filter, change it yourself. Jan 10, 2018 at 18:02

2 Answers 2


Does your manual clearly state that only synthetic oil can be used? My RAV4 hybrid manual says the following:

Oil grade: ILSAC GF-5 multigrade engine oil
Recommended viscosity: SAE 0W-20

SAE 0W-20 is the best choice for good fuel economy and good starting in cold weather. If SAE 0W-20 is not available, SAE 5W-20 oil may be used. However, it must be replaced with SAE 0W-20 at the next oil change.

The only occurrence of the word "Synthetic" in the manual is about cleaning synthetic leather areas.

Considering that my quite advanced hybrid vehicle does not require synthetic oil, I'll bet that your Corolla doesn't need synthetic oil either.

If the dealership offered to change the oil again for free, if I wanted synthetic oil in the car, I would trust them to do it. If they don't, what's the worst that could happen? The oil you already have in your car surely meets the requirements of Toyota engines, i.e. they did not use the wrong oil.

They are providing you very great customer service. Be thankful to them! Next time if you want synthetic oil, be sure to specify it in advance.


The service department has the highest profit margins of any part of a dealership. So, it would be in their best interest to keep you happy and sell you the more expensive oil.

If they are a good business, they will want to keep you happy. It is not worth risking offending you and they gain nothing by trying to deceive you with an oil change that costs them little. If they have been trustworthy to this point, trust they will take care of you.

You can ask to watch, but they may refuse for safety reasons. You can mark your filter and drain plug to see if they get removed, but it would probably not be worth the effort, IMO.

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