Is it bad to use different types of engine oil during each service?

No, as long as you follow the fill interval associated with the oil in the sump

 

The concern here becomes synthethetic vs. conventional. When the turd gen's were brought out for the 2010 model year, the "0w-20" on the oil cap insured synthetic. At that time, all 0W-20's were full syn. They pretty much still are aside from a syn blend or 2 but don't quote me on that. The 5w-20 really is not an issue because of the "5" cold weight, it's the fact that there is a full offering of conventional 5w-20's. Regardless of weight, a conventional oil will not do well in these engines running a 5k miles or longer oil change interval. An old school, 3k miles OCI would be the safest bet with conventional, but the strong history of control ring sticking in these engines makes full synthetic the smart money.

 

Also another poster here is using 5w-30 synthetic in his high mileage Gen.3. I'm beginning to warm up to that idea and think I will start doing that since mine now has 155k on it and after the first 5k mi. on the oil it's starting to use a quart or so.

 

For a G3?

no.

 

I have used 5w-30 on our 2010 Prius II with 168 k miles now since 130 k miles.

Haven’t seen a drop in fuel economy (still get 51 mpg on the Bay Area freeways) and went from a quart every 4500 miles to 16-20 ounces in a 10 k mile oil change interval .

Done some other things, but I switched and haven’t looked back.

Take the plunge.

 

Why is that "preferred" ?
ONE of you needs to "get with the program" and use whatever Toyota recommends; it is usually right on the filler cap.
BUT.....there really isn't THAT much difference between those two grades and either should be fine.

 

That shouldn't hurt anything as modern cars are designed to run on lower winter especially Hondas and Toyotas. 0w to me is a bit over kill since 5w can handle below -35 just fine.

 

I'm also thinking 0-20 is preferred by the marketing people since it may get marginally better mpg's. I came across the service manual for Gen. 3 in Australia (since it's in English I could read it LOL) and the recommended oil in Australia is 5w-30 synthetic. I'm thinking it gets real hot in Australia, right? That made me warm up to the idea of using 5w-30 in Fl.

 

Looking at an Australian 4th gen Prius Owner's Manual pdf I downloaded a while back, it doesn't seem to indicate one preference. It's a surprisingly traditional array of oil grades:

 

Is that also printed right on the cap ?
Either way, get your mechanic on board.

You said "maintenance" manual. Most folks don't have that. What does the OWNERS manual say ??