[Bigphil555]

That is good to know @kevcules46

Hope you get a further 200K too

 

[morRAV4]

Has anybody actually compared the updated design piston and piston rings of the 2az-fe to see if there's any difference?
Have they actually changed anything or does the car just seem fixed after replacement since the pistons are free of sludge?
Trying to decide if it's worth fixing my rav4.

The Toyota fix is no fix at all.
You post is very important: this is a technical issue so I have a long response. I went as hard as possible trying to find the answer and could not find it. The cause is gumming up and blockage of the oil rings and oil drain holes.
(a) I followed all the part number changes for pistons through 2001 to 2018 trying to find the defective pistons. I have seen no side by side comparison of the defective versus "corrected" types, except one suggestion by a youtube commenter that the defective pistons have a notch under the oil ring. This notch was introduced when oil squirters were added. Many performance pistons have such notches, so it is an unlikely cause. Even the Toyota tech guy (car care nut) on you tube could not show the difference in his video on the oil problem.
(b) I followed the low tension ring story (low tension to decrease friction and improve milage). No direct comparison between standard tension and low tension rings is available. I could find no standard tension rings for the 2AZ-FE and there is no tension information on performance rings, such as Wiseco.
I followed production sites, originally thinking that only Kentucky pistons were defective. Kentucky made standard size "B" pistons but the other sizes (A, C and D) came from Japan for US made engines. These different piston sizes are not the cylinder bore size, but refer to accomodating variation in the crank manufacture to save cranks that are out of spec. 95% of pistons are B, so rare engines have a mix of types.
(c) I followed up on US-made versus Japanese, hoping that only US were defective. The oil problem happens at a low rate in all 2AZ-FE regardless of where they were made. The 1AZ-FE has the same pistons and can have the same problem, but was not included in the US TSB (a recall that is not a recall and only in the US).
(d) Oil change interval, synthetic or non-synthetic: no consistent outcome came from this investigation. Some who adhered strictly to the rules had trouble, others who abused their engines with dino oil and long intervals had no trouble. Anecdotal reports of seafoam and other additives having positive effects suffer from reporting bias.
(e) Oil drain holes: number, diameter of hole and angle of hole in piston. I have seen claims that this is part of the new design, but I cannot find a direct comparison that verifies this claim. A proper technical paper should be published if this is the case.
(f) Piston heat hypothesis: it is claimed that the 2AZ pistons run hotter than planned. Compared to the 1AZ, with more fuel, the 2AZ will produce more heat with essentially the same cooling system. The 1AZ does not have the donut oil cooler that was added to the 2AZ. I also think people drive the 2AZ differently: having driven both the 2AZ is more satisfying with the low end torque. Its more fun to lead-foot the 2AZ.
It seems convincing that the notorious head bolt problem is caused by a foam insulator between the block and the plastic intake manifold, causing excess heat. Cooling is clearly an issue. In 2006 oil squirters were introduced to aid cooling as well as an insert in the water jacket to direct the coolant differently. As far as I can tell, these inserts and squirters are absent in 1AZ and 2AZ prior to 2006. Excess heat causing oil gumming could be a cause of a sporadic problem. Toyota tech scientists should publish their data. Small defects in cooling system maintenance might be a cause.
(g) PCV valve and carbon. Oil vapour from crankcase ventilation leads to carbonising of intake valves and piston heads. A bore scope camera down the spark plug tube shows carbon on most piston heads. There is no harm and maybe great benefit from adding a catch can between the PCV valve and the intake manifold. It should have been standard. It is notable that the new 2AR-FE has a built in oil separator (basically a catch can), so Toyota agrees.

Conclusion. I eventually reached the conclusion that the Toyota fix is no fix at all. Just imagine, if you replaced the gummed up old pistons with brand new pistons of exactly the same design what would happen? The engine would be returned to normal and you would have at least 100k miles before the problem might come back. This puts you way out of warranty and one step closer to the junk yard and no longer Toyota's problem. Since I cannot find any reasonable design explanation, that should be all over the internet, this is the only sensible conclusion.

Are there super redesigned pistons? Probably not, since even Toyota wont show us the difference. If your engine is burning oil, then get new pistons. Add an aftermarket oil cooler, keep coolant levels up and get rid of any air in the cooling system.

 

[Ike Carlson]

I have been thinking the same thing for a while now. I thought the difference was a 3 piece oil control ring vs 2 piece.

 

[ForgedPiston]

All these theories are nice, but let me throw out some fact. That two peice oil ring design Toyota used , is a High performance racing piston design for motors that see oil changes every 15 hours and piston replacements every 135 hours, which avoids the oil ring cloggage issue. When you start running these oil rings more than 500 hours, cloggage starts happening.
By the way, its not the piston oil return holes that clog, its the tiny oil ring holes that clog, That notch they did away with, does nothing, as pistons with out the notch will still get a clogged oil ring with that 2 peice oil ring design once you start going over 500 hours.

 

[morRAV4]

All these theories are nice, but let me throw out some fact. That two peice oil ring design Toyota used , is a High performance racing piston design for motors that see oil changes every 15 hours and piston replacements every 135 hours, which avoids the oil ring cloggage issue. When you start running these oil rings more than 500 hours, cloggage starts happening.
By the way, its not the piston oil return holes that clog, its the tiny oil ring holes that clog, That notch they did away with, does nothing, as pistons with out the notch will still get a clogged oil ring with that 2 peice oil ring design once you start going over 500 hours.

Thank you very much for that very useful information. I did not know that the 2-piece oil ring was a racing design. That makes sense. I suppose Toyota was trying to meet ambitious mpg mandates and so used a design that the engineers must have known would clog. Care Care Nut on youtube states that the 2AR-FE avoids the problem by using thin 0W oil and a built in oil separator (catch can). The 2AR pistons look the same as the so-called defective 2AZ pistons.

 

[ForgedPiston]

Thank you very much for that very useful information. I did not know that the 2-piece oil ring was a racing design. That makes sense. I suppose Toyota was trying to meet ambitious mpg mandates and so used a design that the engineers must have known would clog. Care Care Nut on youtube states that the 2AR-FE avoids the problem by using thin 0W oil and a built in oil separator (catch can). The 2AR pistons look the same as the so-called defective 2AZ pistons.

Mahle/Elko-konig are big users for racing application pistons for a typical single compression ring piston, Thin oils may aide. I like the ring design , cause as long as it doesnt completely clog up, oil usage is like zero, and this is even with like 20w50 oils, but again Im talking 15 hour or sub 1000 hour oil changes is my experience, before 30 or 40,000 mile tear down and replacement.

I dont know if a very thin Group 4 type oil would prolong carbon build up in the oil ring ports, but to me street cars, the typical 3 peice ring with larger oil return holes , seems better for longevity to avoid the carbon build up issue (pluggage).

My wife has a 2003 Rav 4 190,000 miles , I add maybe half a quart in 4000 miles, Id say it has a traditional 3 peice oil ring, but I dont know for sure. But I was Surprised, when I saw what oil ring toyota was using for vehicles showing long term oil control issues, that you normally want to see go 200,000 miles without oil usage.

 

[Ike Carlson]

Every vehicle made has at least one big flaw and eventually causes it to be traded off or scrapped. It drives the market and the makers know it. If there was a car that handled great, drove real nice, got real good mpg, and ran forever, they would not sell much of anything else. Toyota has oil problems, dodge has trans/electrical problems, ford has turned into crap, and chevy can't get it right for anything. I have replaced windshields on all of them, and that lets you see stuff that only the builder ever sees. The metal on the new cars is literally paper thin. I grabbed the metal that the windshield is glued to on a ford today and could have balled it up like crumpled paper. It was that thin.

There was an f350 next to it that was in for exhaust warranty. The frame looked like crap. Thin, multi-piece, and not something I would ever expect on a truck. The front arms are pretty much card stock. That truck would never hold up to any kind of truck use.

Corrosion is designed into modern vehicles. Body guys will tell you the same thing. All the new vehicles are half-assed and over priced. I replaced a windshield today that was glued to the roof at the factory. I never thought I would be able to say that, but I can. I have zero interest in a new vehicle.

I'll get some 3 piece rings and fix it myself. Screw that toyota recall/warranty crap.

 

[ravenuer]

Ike, are you chasing kids off your lawn again?
(LOL!)

 

[JFender86]

I just did a complete rebuild on my 08 Camry LE. The difference in the pistons is just the weep holes are slightly bigger. The biggest difference is just the over kit in itself. New pistons w/ larger weep holes, upgraded rings (different compression ring style) and larger oil nozzle diameters for juicing the pistons.