Recommended Maintenance for a Used Prius v?

I'll do a full write-up when I'm complete, at that point I'll have hard numbers to compare.
It's an oil additive you put in with a fresh oil change, and drive it for 4K miles. I'm apprehensive about giving the name because I don't have all the data to say whether it's effective... and I don't want someone to come across this post from a Google search and mistake it for an endorsement or a condemnation.

I bought the car used at 93K miles. Unbeknownst to me, it was consuming oil at a rate of about 1.5 quart/1000 miles. The consumption has not increased or decreased in the last 78K miles -- and I've recorded every once of oil that's been added. It consumes significantly less when not driven at highway speeds = 75 - 80mph.

With the aforementiond experiment, I've introduced two new variables: 1) the oil additive 2) reduced highway speeds.
I would have preferred to introduce just one variable at a time, but reducing speed was necessary because at the higher highway speeds, the oil and additive were being consumed at such a rate that it was impractical. 1700 miles into this oil change, I've seen a reduction in oil consumption. The question is, what's responsible for the reduction? 1) the oil additive 2) the reduced highway speed

I won't know until after the next oil change, when higher highway speeds are resumed.

Stay tuned!

 

Or 2 oil changes in case the additive gets washed out of the system.

 

I don't follow?

 

I believe the concern is residence time and if it remains or is carried out by the drop in oil level and not replenished.

 

I'm not trying to be intentionally obtuse, but I still don't follow. The additive's job is to help "dissolve" build-up. Once it's removed and no longer in high concentration, it will cease to work, won't it?

 

Or is the additive making the oil thicker so it does not go down as fast?

 

I think @Raytheeagle saying:

You've put in the additive. Now say 1000~2000 miles down the road, your oil level's dropped so much you need to top up, diluting the additive. So do an early oil change, with another fresh dose of the additive. You want to keep the concentration of additive in there for a given number of miles.

Another thought: when you top up the oil, make the top up 90% oil and 10% additive (percent as example, whatever is needed to maintain the recommended proportion).

 

Haven't had internal engine problems. Got car from neighbor with 194,000.
I don't hate Toyotas...have 3 but the 2013 Prius has had way more problems than my Camry (315,000) and Previa (430,000) both of those only a few hundred in repairs I did myself.
2013 was all highway miles from Houston to Orlando as previous owner had a business in both citys.
It's the hybrid stuff that goes out and is very expensive especially if you can't do it yourself.
I bought the car thinking it would be like my other toyotas.

 

No, it's not an STP-type treatment that thickens oil. It's designed to dissolve build-up inside the engine.

 

OK. I see what you're getting at. Yes, I've already accounted for that. At this point, I'm only down 1/2 - 3/4 of a quart. I'll let it get down to a little over a quart low before I add additional oil. If that time comes, I do intend to mix some additional additive in with the oil to maintain the proper concentration.

One strategy I've taken to increase "exposure" to the additive is to allow the car to idle in the driveway. Yesteday I let it idle all afternoon while I worked in the yard. The ICE only comes on a few times an hour for about 5 minutes. I figure this is allowing otpimum exposure to the treatment, while mimizing oil consumption.