Adding 1qt/2K, ever need to change oil?

...yes but I took minority view that he may be OK, can I get partial credit for independent thinking?

 

Absolutely!

Maestro8 is another story!

 

I find this a fascinating thread. The OP has asked a valid question and has received numerous answers that don't fit his logic. Although I have been changing oil in my cars for over 60 years, I don't consider myself an expert. I use Fram filters and anyone who reads the forums knows that they are consistently judged as junk by the experts.

I will be quite satisfied to hear that he chooses to continue adding oil as needed, and change it when he is ready. That would not be my choice, but it's his engine. Torture tests have interested me over the years, so my request to the OP is that he keep us posted. I wish him good luck!

And, no, I don't have a Prius, but my wife just bought a new Prius V.

 

The OP asked a question on a forum of similar vehicle owners that have a variety of life experiences not in a forum of mechanical/lubrication engineers. I have only tried to explain to someone who might not understand what makes engines tick.
I do not consider myself an expert in anything and your definition of an expert probably differs from mine. I grew up building engines for race cars, and currently I manage a Fleet of 1800 cars, does this make me an expert, no it doesn't. I know that some engines seem to be bullet proof and others are extremely fragile. In this case the OP's car has made it this long and no one can forecast how much longer it will last. Most of the people you will find here are here to help others and learn about their own car, that is why I am here.

There are many places on the net where you can find plenty of late night reading material on lubrication.


Basic Lubrication Design - Bob is the Oil Guy

 

You're leading us into the "No true Scotsman" fallacy, but I'll play your game.

...because the amount of heat created in the combustion chamber limited. That "dirt and grime" is a composite of many materials, including particles of metal and various grit that makes it past the air, fuel and oil filters. The combustion chamber is not a blast furnace; it's not going to incinerate everything that makes it in!

Even if the combustion chamber did manage to heat everything to its vaporization point, we're not guaranteed that the vapors would make it all the way out the tail pipe. The engine is not at thermal equilibrium; there are hot and cold spots throughout, and the vapors could condense right where we wouldn't want them.

Do we need to explain this in even further detail? If so, grab your thermodynamics book...

One does not need to gather statistics to know the effects of abrasives inside the combustion chamber. Just send your own oil out for analysis, you can see for yourself... it's not going to be clean after 5k miles, by any measure.

 

Caught you contradicting yourself , AllenZ. You stated at the beginning of this thread that:

My goal is to lower the cost, and I am willing to take reasonable risks backed by technical knowledge.

So which is it AllenZ?

rwyckoff has lumped together virtually every response to your initial statement so far as non-technical and basically of no help to you. So "technically" he's on your side apparently. Nothing wrong with that.

You've been provided with some sound advice and at absolutely no cost. Most of us are merely trying to be helpful and are not debating the merits of saving the cost of about 2 qts of oil and a filter if you changed every 5000 miles.

So, since none of us has provided convincing "technical" reasons why you shouldn't be doing what you're doing PLEASE continue to do it. Best of luck to you. You're going to need it. (just my non-technical opinion).

 

...probably even the worlds lube experts do not know when a Prius leaking oil, when the leak is big enough to avoid refills, if there is no test lab data. So the idea of asking for expert testimomy on this situation is a little problematic. Many on Prius chat use lube oil test labs available to check quality, that would be the obvious answer. If we are saving money, then that option is out. Some sort of quick appearance check (paper spot test or equiv) would seem advisable to make sure nothing unexpected is happening.

I still think filter replacement after max 10K is suggested. If you are losing 1qt oil every 2K miles, and you lose another 1-qt in the filter replacement you are replacing ~50% oil inventory just in that one 2K period. I gotta think Mobil-1 or equiv. high quality synthetic may help to prevent the gunking that may have caused the oil leakage, and may help to flush it out. There is also Mobil-1 5W-30 "High Mileage Formula" which is designed to reduce leakage.

 

I changed my view now that I better understand what you asked. Technically you don't need to change it. I'd wager a bet that if you only added oil you would likely have a non oil related issue before an oil related issue. I really do not know of any engine failures in last 20 years in an engine that had oil.

 

More about oil than most will ever want to know.


- Bob is the Oil Guy

 

How's your spin?

As Mr. Horse used to state on the Ren and Stimpy show:

Initially you were trying to save a few bucks, now you're on a quest to prove all the naysayers wrong.

Whatever spins your wheels, dude.

 

Put your money where your mouth is. Stop changing the oil in your car and tell us what happens.

Arguing from a point of ignorance only proves your ignorance, not your argument.

 

I think I can put this discussion to rest. The answer is that if you are burning oil, and add 4 quarts of oil every 8000 miles, you have not removed all the old oil in 80000 miles, some of the original oil is still there, whereas if you change your oil once every 8000 miles, all the oil is changed once.
If you car holds 4 quarts, and after 2000 miles you have 3 left and add one, then you have 75% old oil, 25% new oil. The next time you add a quart at 4000 miles you have 3 quarts of oil that consits of 2.2 5 quarts of the original oil, 0. 75 quarts of the oil from the first quart added and 1 quart of new oil. At 6000 miles, you have 1.6875 quarts of the original oil, .6625 quarts of the first quart added left, and .75 quarts of the second quart added and 1 quart of fresh oil. At 8000 miles you add your 4th quart, but have 1.4 quarts of the original oil, .5 quarts of the first quart added, etc. As you can see there is always something left from each quart added, so you never do a complete oil change.
It is true that you add some fresh additives each time, but not enoug so the old stuff never gets completely removed, and you have sludge start to build up, water retention which turns the oil accidic, and metal particles building up. A long term recipe for disaster.
So, if you would normally change your oil once every 5000 miles, you can push it to 6000 because you are replenishing some additive, but do not go much more. If you use Mobil 1 extended life, you can go to 15,000 or maybe 20,0000, but you should change the filter more often. The bottom line, you would be foolish not to change your oil completly periodically. I have a friend that had a new "oil change plan" for his leased car. He figured that he could get away without changing the oil at all on his 2 year lease. Well, a few weeks before the 2 years were up, the engine threw a rod because the oil no longer was lubricating the engine.

 

From a practical point of view. Since you still need to change the filter, then you still need to get under the car, you still need something to catch the oil, you're still going to get your hands dirty. Are you really going to save that much of anything (time or money) compared to if you drain and refill the oil at the same time? For me personally, I'd say that by the time I'd made the effort to change the filter it would add no more than a few minutes extra to do the oil as well.

Also, I think it's extremely optimistic to assume that the "bad guys" in your oil, like sludges and gums, are going to get burnt up at the same rate as the "good parts" of your oil. Personally I think that the engine would have a higher risk of sludging up if you only ever top off the oil.

 

10-12K is acceptable with synthetic oil only.