2GR-FKS burnt valves and blown gaskets octane related?

I'm seeing these threads pop up about exhaust valves burning, head gaskets blowing, and engine blocks cracking. They don't seem to be associated with any particular cylinder or specific spot in the block that would indicate a design issue and they're few enough that it could just be a QC issue for an unlucky few.
I wanted to get some opinions about whether or not this could be an engineering/EPA compromise problem related to fuel octane?

I'm by no means an engine mechanic, but back in the day anything with 10:1 compression ratio required high octane fuel. I know this we in part limited by what fuel/timing management was able to do, but the principle of compression and detonation hasn't changed as far as I know.

I've helped keep my dad's 350 small block running for years. It has flat top pistons and solid lifters making 175psi compression on each cylinder. We don't use anything less than 91 octane in that engine.
I'm seeing that the 3.5 is supposed to produce something like 195psi in a healthy compression test, but it's supposed to be safe to run 87 octane and it just doesn't seem ideal to me. Is it reducing compression by leaving the exhaust valves open a bit longer when detecting pre-det? How long would something like that be good for an engine? What happens if the management system doesn't get it perfectly right?

I've always run 91 to 93 in my truck since I found how much better the engine feels compared to the first few low octane tanks I tried after buying it. I know it's not economically ideal, but something just bothers me about running lower compression fuel in a high compression engine.

Now I'm seeing these posts of burned valves and blown gaskets, which I've heard of being associated with pre-detonation, coming up in relatively low milage engines and can't help but wonder if Toyota is riding the line between efficiency and economy a little too tightly?

I'm at about 50K now and I guess I'll find out one way or another, but I'm really hoping to come out on the positive side of this.

Feel free to tell me how much I don't know about engines...

 

Compression is more than just pressure…
You can run 87 in a 10:1 with proper chamber design.
That’s why a dished piston and a small chamber makes more power than a pop up piston in a big chamber. Can’t compare a 350 to it. the heads don’t even have traditional exhaust manifolds. It’s overly complex for the amount of power and efficiency you get from it. That’s been plaguing all manufacturers, they come up with something that’s easy or cheap to build and it models well for the other boxes except it doesn’t meet consumer expectation on longevity.
like I have a Hyundai and I’m just excited it made it to 60k miles

 

The issues seem to be in Cylinder 1 and 3 more than anywhere else, and there have been at least 3 or 4 manual transmission trucks that all had it on cylinder 2. No idea if the transmission relation is just a weird coincidence or what, but that is what I have observed, and I am pretty observant when this problem comes around.

There have been posts for failures on all 6 cylinders, so certainly none of them are immune, but the problem children seem to be 1-3 more than anything else.

I think octane could contribute, but that it isn't a death sentence to run 87 octane. I think there are still unlucky failures that would have failed regardless of the octane. But I also think that running higher octane could certainly help to minimize the detonations that could contribute to wearing out a valve early over time. However, I still don't know why most of the time the problem is on those 3 cylinders more than the other 3. Could be cooling isn't as good in those areas as well, or maybe actually a head design problem that just isn't always problematic.

They are also able to more effectively run a higher compression engine on lower octane by using direct injection...so that is partly why they are able to get by with it without grenading the engine. That does not mean there are not benefits to using higher octane, though.

It's hard to say and since Toyota chose to ignore the problem entirely, we don't really have any real information about why the failures occur and what, if anything can be done to prevent them. Only thing to do is keep on using premium and see if you ever make it to high miles problem free...although of course there was a chance that you would have made it to high miles anyways if you had run 87, so it's not perfectly determinate that octane is the reason you didn't have a failure. For what it's worth, I have run nothing but 93/91 (91 when traveling out of state, Texas has 93 almost everywhere), for several years, in an attempt to hopefully prevent potential issues as well, with the valve issue being the top priority I'd like to keep away.

I do have a feeling that we will hear about many many more valve failures as the years climb. The engine is no longer in mass production, so no more new trucks every day diluting the problems. Now it's time to sit back and see how the existing ones age.

 

It's always been a compromise between cost, efficiency, emissions, reliability, and longevity. With emissions, fuel economy standards, and cost getting crazier every year manufacturers are pretty much throwing reliability and longevity out the window in order to meet emissions and fuel economy standards in whatever way possible and keep cost down even if that means the engine/transmission won't last as long.

That being said I doubt octane has anything to do with it, there are many engines out there running higher compression ratios and not having issues. It may be a tuning or materials problem but there are millions of these engines on the road and only a small fraction of them are having issues unlike some other engine families where your all but guaranteed to have a failure.
As a tech that gets to see many of the blatantly obvious engineering/materials flaws in a variety of vehicles I'd much rather own a Toyota or Honda product than pretty much anything else even though I'm not all that impressed with their late model stuff.

Also while variable valve timing is used for economy and emissions, pre-detonation management does not hold exhaust valves open to lower compression. They mainly use ignition timing and air/fuel ratio management (and also injection timing when in DI mode) to control pre-detonation.

 

This will be the legacy of the 2gr-fks.

It was put into the 3rd gen Taco with 2 purposes front and center...EPA regs and quick/cheap solution using an existing Toyota minivan/sedan motor as a base. It was never meant to be indestructible as Toyota knew when the 3rd gen was put out in 2016 that they were going away from the NA V6in the very near future. The 2gr-fks was a band-aid solution between gens 2 and 4.

Aluminum block, aluminum head, Atkinson cycle, plastic coolant pipes = not built for reliability.

That said, I willing to wager that most people experiencing catastrophic engine failures don't run premium gas. Toyota has said many times they've never even tested the Tacoma with 91 octane.

 

Isn't damage due to pre detonation apparent to the pistons when an engine is subjected to low octane?

 

Another factor might be people not using top tier gas.

 

I've thought about this too.
Definitely bought gas and 20 miles later thought the engine didn't feel right. I've recently stopped going to a particular station due to how rough the truck ran the last two times I filled up there.

 

Something to note is that I have only seen failures posted up about the Highlander and Tacoma...and it seems far more common on the Tacoma out of those two. But, Highlander owners are likely not on the forums like we are, so that part of the equation could just be due to the differences in how much word spreads amongst truck owners vs family SUV owners.

What is interesting is that the Tacoma and Highlander engines use one design for each cylinder head, while it's a different set of part numbers for the other engines (Lexus, Camry, Sienna, etc). That makes me think it's probably a design flaw in the Tacoma/Highlander cylinder heads....but then why are the failures so rare? Hard to say. It's also odd that so many of them make it such a long time and then throw the code. Such as 80K, 150K, etc. It is just an odd problem that I can't really wrap my head around because there isn't enough concrete information. All we know for sure is that every single one that has failed so far has had a leaky exhaust valve.

 

Modern engines with a properly working ignition system and knock sensor/s will dial back timing anytime damaging knock presents itself. Running an engine [] this close to spark knock is the most efficient means to get fuel efficiency, back it off and you lose power and fuel economy, advance it too much and it damages the engine because the igniting fuel is trying to expand before the piston is close to TDC and the flame wall advances too much trying to force the piston down before it reaches TDC.

I get far more spark knock running 87 in my 93 Miata then a more modern engine while 93 octane is perfect for it. It's not like it's high compression or anything, and 93 isn't mandated, but it DOES like it far better then 87. It's not bad or severe knock but I can hear it under load. Would it be fine? Maybe, but a few extra 20's a year means little VS tearing an engine down or replacing it.

A bad knock sensor would certainly cause damage on a modern engine if spark knock were present much of the time under load, remember, we need a controlled smooth flame propagation, not a detonation.

 

Also, variable timing holding the valves open to reduce compression would increase emissions and foul catalytic converters. It would also mean that all cylinders would be subject to valve issues, not just 1 and 3 primarily.

 

We didn't really have the level of monitoring/control we have now so engines with older tech could have slight leakage and you wouldn't know the difference until it got bad enough to develop a misfire, which may be hundreds of thousands of miles.

Now that we are able to monitor and control combustion per cylinder insead of per bank any minor deviation between cylinders sets a code even if the engine appears to be running fine and may continue to run fine for a long time.

 

Very true, I have mentioned that in other threads as well...we have probably had more of these problems than we are aware of, and just don't know it. The downside is that a trouble code holds you responsible when you go to get emissions done, if you live somewhere where that matters. That is a huge downside if you can't pass inspection because your truck is more capable of diagnosing itself and lets you know that you need to spend $7k to get the light to go away again. I bet most would rather just not know.

I've already said it, if it happens to me, I'm not doing anything about it for a while. I'll figure out how to deal with the emissions, but I'm not spending $7k for a cylinder head job. I'll buy a JY engine and swap it myself before I'd do a head job.

 

That's the bane of modern emissions regs/tech, some of it is a good thing but it has gotten completely out of hand.
At least so far gasoline engines haven't gone the way of diesels where if your emissions system has a fault you get a mileage/time countdown, once that is up you are stuck in idle only and/or may not even be able to start the vehicle until the fault is fixed and all the hoops are jumped through to reset/satisfy the system that it's working properly. It doesn't care if your in the middle of nowhere or have to wait until a shop has an opening to fix it.

 

Like the dreaded air/fuel imbalance code.
It’s incredible that we can monitor this stuff at such a level. Still no fun to diagnose at times. And can be a an issue for some in emission inspection states. Diagnosing those codes can be quite hard without lots of labor.

Bit still kind of cool how we can “see” what is happening at such a small and fast rate.

 

Octane and compression have nothing to do with it. You can burn an exhaust valve on an 8:1 compression engine just as easy. Exhaust valves are cooled by the valve seat. So either the something it wrong with the seat or something is causing the valve to hang open.

 

That's a load of crap! I've been filling my vehicles with "whatever" gas for 50 years and never had an engine implode.

 

Not sure...I guess I haven't seen many of those threads. Toyota sold almost 2 million of the 3nd gen. Having a handful of failed engines is within manufacturing and parts tolerances. Other things to think of; we're also running the lowest output version of the 2gr-fks, an engine they use in all sorts of vehicles all over the world. Which generation of 350 small block your referring to, if it's carbureted or throttle body injected, its intake charge dynamics are so drastically different that it is comparing cannon balls to missiles. 11.5:1 compression isn't very high by modern standards.

 

All a higher octane rating means is the gasoline's ability to burn slower and in a more consistent stable manner. 87 burns faster and in a less stable manner which is why an engine knocks [pre-ignition] more on low octane fuel then high octane. High octane fuel doesn't give you more power, it allow the engine to produce more without damage. If you rated diesel by octane rating it would be in the 8-15 range which is why you can run such high compression, the compression itself ignites the mixture of air and fuel. [if you ever had a BB gun and added a drop of oil after the pellet, it dieseled and actually ignited the air/oil mix. bad for the seals but fun for the shooter]

 

An "implosion" would be unicorn rare.