Reviving a 270K mile Highlander Hybrid

[cRiPpLe_rOoStEr]

So, presumably what dictates the major differences between hybrid versions of the engine and their non-hybrid counterparts are the cylinder heads and the ECU mapping, with most of the hardware being identical? I'd also be cautious about oil sump clearances, even though it might not be much of an issue for this engine.

[Drifter]

I think the heads were all the same as well. I'll confirm later.

Tonight I cleaned up the pistons a bit more - #1 was pretty sludged - I doubt the oil ring could function properly - and that would be if the oil holes hadn't been totally clogged. Here it is towards the end of my soaking & scrubbing:



In the process of cleaning the underside of the piston, I discovered they are in fact Toyota pistons (note the tiny hole going to the oil ring. There are 4 such holes per piston, 3 of which were totally clogged on piston #1:




My frugality is costing me quite a bit of time. It is incredibly difficult to get precise bore readings with cheap Amazon telescoping bore gages and a cheap micrometer.

Did I expand the bore gage the same amount? Was it in the same location? Did I line it up in the micrometer the same way? Did I tighten the micrometer the exact same amount (it has a ratchet, but it is inconsistent)? All of those factors introduce variance so I end up taking ~5 readings per location to try and get a better feel for it:


Without fail, the bore on the piston-pin axis ("A") appears to be like new, but the piston skirt axis ("B") has worn/ovalized about 2 thousandths. There does not appear to be much taper between depth 1 (10mm from top) and depth 2 (40mm from top)

The piston skirts all appear to have had about 1-1.5 thousandth of an inch oil clearance when new (and now have about 3 thou max clearance on the ovalized portion of the bore). 5 thousandths is max so in theory I could probably get away with honing the bore and using new rings - assuming everything else checks out.

For funsies, I checked the ring gaps for the #1 piston. They were all towards the tight end of the standard range, which surprised me. I would have expected more wear. Top ring appears to be cromoly or otherwise plated. Middle ring seems like a cheap/standard ring. the oil control ring is quite a bit different than the ones I'm used to from Supras and MR2s - by contrast it appears to have much finer holes that are easier to clog...

The crankshaft would definitely need a polish. The rod journals for the middle cylinders look pitted in places (but you can't feel it with a fingernail):

[cRiPpLe_rOoStEr]

Originally Posted by Drifter

I think the heads were all the same as well. I'll confirm later.

All other hardware being equal, it's quite intriguing how the 'Yota Atkinson-cycle hybrid engines achieved a greater static compression ratio.

[Drifter]

Lower half of the engine is now at the machine shop. They were unfazed by my various concerns and from a visual inspection think it is a good candidate for a light hone & crank polish with standard size rings/bearings. They'll know more once they take their own measurements, but they estimate a ball hone would remove just 0.0005" from the cylinder and still leave me inside the factory service limit.

I'd kind of prefer to bore it since I don't see a hone/re-ring lasting another 250,000 miles, but this machine shop can't bore these cylinders because this block's main bearings are right below the cylinder which doesn't allow enough room for this machine shop's tools.



Their boring machine needs to punch all the way down through the bore, but on the 3MZ the main bearings overlap the cylinders and don't allow this. A different machine shop could do it, but the handful that are well-rated are backed up weeks to months (my first choice wouldn't even accept any new jobs). But I suppose if I was going to attempt a near Toyota-quality rebuild, I'd really want to find/build a torque plate so the cylinders could be stressed into their assembled shape when the machine shop did the actual boring. Perfection is the enemy of good?

Originally Posted by cRiPpLe_rOoStEr

All other hardware being equal, it's quite intriguing how the 'Yota Atkinson-cycle hybrid engines achieved a greater static compression ratio.

Unlike most of Toyota's other hybrids, 3MZ-FE in the highlander & RX400h was never converted to run an Atkinson cycle which I think it kind of a bummer (for fuel efficiency anyway). According to automotive press in 2005/2006, the 3MZ hybrid was mainly developed for the Lexus RX400 where power & refinement trumped fuel economy. It was just carried down to the Toyota Highlander to spread development costs out over more units.

The Highlander Hybrid would get the Atkinson cycle in 2011 when it switched to the 2GR-FXE engine. The 2010 & 2011 had the same chassis, but the Atkinson cycle 3.5L hybrid in the 2011 is rated at 28/28 mpg (city/hwy) vs 27/25 mpg for the 2010 3.3L hybrid (and 17/23 for the 3.5L non hybrid).

Those EPA ratings and retroactive estimates based on current methodology - the highlander was rated at 33/28mpg in 2006 (just like the 2006 prius was rated at over 50mpg)

[Piotrsko]

I agree a hone to limits and standard pistons ain't going to quite cut it. You have a piston slap (?) Going on so you really need a better fit on the skirt or better skirts. However, back in the day.... honing to 005-010 oversize was common but time consuming. They lasted just as long as bore and hone..matching pistons to bore was required. Engine crank looks like it sat with crappy oil for a long time since those look like acid pits.

[Drifter]

I'm reasonably confident the skirt wear was from overheating since the piston-to-wall tolerances were essentially identical but only a couple of pistons exhibited the wear.

Regardless, the machine shop called with bad news. The rear head is cracked below the valve seat which was what was pressuring the coolant. They can weld it, but it would add 3 weeks and a couple hundred extra dollars. At that point, I'd be looking at paying $1300-1500 in parts and machine shop fees to rebuild an engine towards the sloppy side of the tolerance limits since they can't do a proper bore on the 3MZ with their equipment (and the other machine shops are turning away work).

So I ordered a documented 126,000 mile engine from LKQ for $1250 shipped (and should be here in 5-7 business days). Their listing showed a rear-ended highlander with a 126,000 odometer picture. Plus the VIN matched a car which last sold with 95,000 miles in 2019. Assuming the Vin on the delivered engine matches the Vin on the car, I think it will likely be as good as a re-ring rebuild.

So basically I'm back to where I was a month ago, only now I'm committed to doing the install myself. On the plus side, what I would have paid in labor to a shop I've gained in tools and some extra parts (like a CV axle, new control arm bushings, new rear coil-on-plugs, etc).

[cRiPpLe_rOoStEr]

Originally Posted by Drifter

Unlike most of Toyota's other hybrids, 3MZ-FE in the highlander & RX400h was never converted to run an Atkinson cycle which I think it kind of a bummer (for fuel efficiency anyway). According to automotive press in 2005/2006, the 3MZ hybrid was mainly developed for the Lexus RX400 where power & refinement trumped fuel economy.

I never took a closer look at the Lexus RX of that generation, and most of the ones I used to see were non-hybrids. Odd enough, only recently I have seen a more considerable amount of the hybrid of that generation...

[Drifter]

Yeah, I think since the hybrids hold their value a bit better they disproportionately survive large repairs & small collisions that might scrap the gas-only versions.

Here is the crack. Now that it has been hot-tanked, pressure tested, and marked I feel a bit silly not seeing it before:



For perspective here is the cylinder that was clearly getting water:


And the corresponding chamber:


Close up shows some clear red flags (like how the edge of that exhaust valve has been steam-cleaned, but not the whole thing):



To be fair to myself, I did tell the machine shop to be extra vigilant when pressure testing that head because the head gasket didn't look bad enough to blow coolant out of every seal. Still, I wish I could get the last 3 weeks back...

[redpoint5]

I'm proud that I can name and have basic understanding of most of the parts in the pictures.

...still don't think I see the crack nor would I ever dream of trying to solve such a problem. Chances of me getting everything back together, with no extra bolts leftover, within spec are close to none.

[cRiPpLe_rOoStEr]

Originally Posted by Drifter

Now that it has been hot-tanked, pressure tested, and marked I feel a bit silly not seeing it before

Sometimes it's quite hard to notice a small crack just by the unaided eye, even though they might do a lot of damage to the engine.