Well I sort of messed up too, but here's the problem:

I have an '04 FX4, and I've been using synthetic oil for a while now. I just hit 19k miles, and it was due for an oil change. I've been getting my oil changes done at a local dealer, but this time around I forgot to tell them that I wanted synthetic.

I figured that they would be bright enough to check my records, or even look at the sticker on the window to see what I got last time, but nope, they didn't.

So they put in conventional oil, and when I went to pick it up I told them that I had been using synthetic. They told me that if I wanted synthetic, they would have to charge me for the conventional oil that they just put in, and then charge me again for the synthetic. I told them to forget about it.

Now I am wondering, can I go back to synthetic on my next oil change without getting an engine flush?

The tech at the dealer told me that new conventional oils are really good these days, and I shouldn't have a problem. He also told me that the way the engine drains, there should only be about a cup of the conventional oil left over when I switch back to synthetic the next time, and that I shouldn't need an engine flush.

Should I believe him? What would you guys do?

Thanks in advance for your advice!

 

I'd just leave it in there for this oil change, especially if they used Motorcraft oil that is a semi-synthetic anyway. You should find out what they used.

Conventional oils are pretty good, and having a little conventional in your next synthetic fill is no big deal, either. They mix just fine. A flush is just a waste of your money.

The only thing you might do is decide to change it a little sooner than normal - but even that is tending towards way over cautious.

I've had trouble finding the Mobil 1 5W-20 around here, so I use it when I can find it and use Motorcraft semi-synthetic when I can't. If I couldn't find either one I'd throw in a good brand of conventional. And if I ever got in a position where I was a quart low and only had conventional to top it off with, it would go right in with whatever else was in there.

Bottom line - don't worry.

 

It doesn't matter.

Too many people think too hard about oil.

 

And not enough about filters. Some people will pay 60 bucks for synthetic oil that can go 15,000 miles and then cheap out on a filter for $2.00.

 

Only problem you should worry about is not having enough oil. IMO all the major brands be it synthetic, blend, or conventional will do the job as long as it is changed at the proper time frame for the vehicle.