My theory on why some Gen 2s consume more oil after 150k miles

Well, the only problem is Yaris (and its predecessor Echo) with the 1NZ-FE engine is well known for NOT consuming oil, even at very high miles (reported up to 500,000 on yarisworld). My understanding is the difference between 1NZ-FE and 1NZ-FXE is the intake valve timing and different pistons and rings. Specifically, LOW TENSION rings. I think this is where the source of consumption lies. Those low tension rings will be less resistant to ring grove contamination and more susceptible to weakening from normal wear.

 

While 0W20 oils do contribute slightly to oil consumption, the effect is not that great.
Why? Because countless UOAs show that typical 5W30 turns into 5W20 in no time. This is why the switch from 5W30 to 5W20 (or 0W20) oils is not such a big deal.

 

If 5W-30 turns into 5W-20, what does 0W-20 turn into?

0W-10?

I think it is a mistake for 2G owners who live in hot ambient temps to use 0W-20 unless they can tolerate unnecessary engine oil consumption. To me, "hot" is sustained temperatures above 90 degrees F.

 

No, the XW20 oils are more shear stable and don't shear out of grade. BTW, the lower grade is now SAE 16.

 

It just seems like once the federal government has set forth a certain mpg goal to reach, the manufacturers all went to 0w-20 oil to help achieve this goal. Regardless if the engines were designed for it or not. And when you bring it to the dealers attention, they come back with a "oil consumption test" knowing for a fact it won't do anything. They spec the cars to be normal burning 1 quart every 600 miles. CRAZY!

I don't believe Honda or Toyota cars had many problems with oil consumption until switching to 0w-20 oil. I don't think all engines are compatible with this oil. You can read on the Honda forums that many 4 cylinder cars that use the 0w-20 grade is experiencing premature oil consumption. To make matters worse, they all have a 10,000 OCI now and it's causing owners to run low on oil. I would think someone that has purchased a new car shouldn't have to constantly check the oil levels to make sure it's not low. That's the reason you buy new.....otherwise you would save money and buy used.

 

Hypothesis, not theory.

 

No offense, but I have to disagree with you and here is why. I used to have a made in 2002 Corolla that developed oil consumption at the "old age" of 70,000 miles despite oil changes every 4-5000 miles (every 6 months) with quality 5W30 oils, the book specified 7,500 miles OCI at that time. Being a curious person that I am, I researched why that was and discovered that Toyota make a series of mistake in the engine design with the most important being too few oil holes in pistons. Just like GM did designing Saturn, famous for it's oil consumption. Later, similar mistakes were also made in Toyota's 2.4L engine (2AZ-FE) that also developed excessive oil consumption, but not as widespread as the 1998-2003 Corolla. 2AZ-FE was also specified for 5W30 oils.

On the other hand, newer Toyota engines specified for 0W20 such as 1.8L 2ZR-FE in the newer corolla are totally free of oil consumption problems. Notice that a similar Atkins cycle engine with low tension rings is fitted in 3rd gen prius (2ZR-FXE) does have the same oil consumption issues as the gen 2 prius. So, this should provide enough clues.

 

Does this possibly have to do with the initial 0w weight at startup? The Corolla starts and stays running so the oil can quickly get to the 20 weight where as the Prius will start and many times shut down numerous times before getting the oil temperature to warm up to a 20 weight. Maybe this longer time for the oil warming up is an issue....especially as the engine ages a bit and the engine is not as tight as it was when new. The oil is too thin at startup temperatures and taking too long to warm up to a 20 weight.

But....it also seems the people in the colder climate doesn't experience this burning as much (like Europe). Maybe the metal parts expands and contracts based on temperature?

I'm not an engine guy, just thinking to myself.

 

duplicate post, sorry

 

I don't think the Gen 2 originally shipped with 0w oil, but I could be mistaken about late model Gen 2s.

 

10+ generation, 2009+

 

The engine oil is never too thin at start up. It's actually too thick. Then it thins down with warm up. This is why oils are moving up in viscosity index numbers with oil technology advances. The SAE scale is confusing you. the 0W part at cold temps is much thicker (hundreds or thousands of cSt) than 20 at nominal engine temps (under 9 cSt @100C).

 

Just a thought, but I've seen sludge in the upper part of an engine keep the oil from draining down into the pan like it should. This excess oil in the upper part of the engine can get drawn in around worn valve guide seals. It can also get sucked in the PCV valve. Higher RPMs will make this worse since the oil pump will be pumping more volume of oil.
It could also be a sign of intake manifold gasket allowing oil to get sucked into the intake under low vacuum/high throttle conditions.
I don't have any specific information that a Prius may have these issues but these are some areas to consider.

 

Oh yes, check your spark plugs. Oil getting sucked in the intake will often result in at least one spark plug with oil residue. I had a minivan that would fowl the plug in less than 3000 miles.

 

Your understanding of oil viscosity is way off there JC, all oils get thinner (runnier) as temperature increases. Don't worry though, very many people get confused by the somewhat archaic oil weight-number system. The simple explanation is that you just can't compare the first and second numbers in an oil spec like 0W20, because they have no relation to each other.

Think of it like being in completely different units. Say for example I was to quote you two numbers, the first representing the current temperature inside my house and the second the current outside temperature. Ok, so if I tell you the numbers are 20/50 then you're going to think it's warmer outside (50 degrees) than inside (20 degrees). Wrong! I just gave you the outside temperature in degrees F but the inside temperature in degrees C, so inside is actually warmer!

Ok that seemed like just a stupid childish trick on my part right, giving you the numbers in two different units so as to deliberately mislead you. But that's exactly how those oil numbers like 5W30 etc work. You can't compare the "5" with the "30". Despite both being numbers, they are not directly comparable.

BTW. You can (somewhat) meaningfully compare first numbers with other first numbers (like the 0 in 0W20 and the 5 in 5W30), and also second numbers with other second numbers (like the 20 in 0w20 with the 30 in 5w30), but you can't meaningfully compare a first number with a second number.

 

How strange I just had a brain fart. I thought I knew how the viscosity works, don't know how I came out with what I wrote. Must be my other half that didn't understand that wrote that.

Now explained again, the knowledgeable part of me understood. Strange.

SM-N900P ?

 

Ok everyone, lots of good discussion on oil burning here but I have to believe that the OCR's and to few oil drain holes are the culprit and here is why. Ema's oil burning has shown not noticeable but dramatic improvement in the last 10,000 miles or so. She was burning 1 quart every 1,500 miles, sometimes fewer miles, and is now burning 1 quart every 2,000 minumum and regularly 1 quart every 2,500 miles or better. Ema now has 367,000 miles!!!! No amount of "engine wear" can be repaired after 350,000 miles so why is she burning less oil?

See my post on page 5 in this thread here:
Burning oil at same rate regardless of oil thickness --- What does it tell us? | Page 5 | PriusChat

Or essentially the same post in this thread, also page 5:
2008 Prius - burning oil at 135,000 miles | Page 5 | PriusChat

I have seen increased oil burn at higher RPM's as was speculated on in this thread so I think that is valid. BUT I have not seen this same increase since my oil burning has slowed with the use of non-ethanol gas. I think this adds significant weight to the "it's the rings" line of thinking. If they are cleaner/free the higher RPM's do not make the oil burning as bad.

I am pretty sure in one of the threads above there are a lot of pictures of an oil burning engine that was taken apart and it actually shows very little wear inside. Again, back to the rings issue with them being stuck, gummed, sticking, drain holes plugged, etc... My last 8 tanks are 51.93, 48.35, 51.81, 48.51, 47.17, 48.66, 47.21 and 45.25 MPG with non-ethanol gas and those are consecutive tanks. Before that I was not making nearly the effort to get non-ethanol that I am now and had ethanol fillups mixed in but was still using the Lucas Oil Ethanol Stabilizer. I think that was helping the oil burn but not the MPG and engine.

Anyway, I thought you might be interested in someone who is actually dealing with "The Burn" in a high mileage Prius. My opinion - The rings get "sludgy" and make the burn worse. Cleaners such as SeaFoam, MMO, etc... help but take time. Good gas that is non-ethanol also helps, probably reducing/eliminating "ethanol varnish" but also takes time. Once the sludge/dirt/crap is there it doesn't want to come out easily, lol.

Would be intersting if someone has ever pulled a high mileage engine just replaced the rings and put it back in as a test? I know I know, if you are going to do that why not replace the engine entirely. "For the educational experience." LOL

Happy driving,
Chris

 

Here is 1 vote to nominate Chris to replace rings on his high mileage engine

SM-N900P ?