Periodically drive hard to reduce EGR clogging?

As far back as 1979, no car of mine or my family's that had EGR was ever free of EGR troubles.

The '79 one had to be reamed out, like, yearly. And didn't have any OBD codes to tell you when.

The Ford 2.8L had a different sort of issue, the valve would work ok, but the potentiometer position sensor on it would go flaky after an absurdly short life, at around $130 every replacement.

 

Have you never owned a Gen2 Prius?

The EGR design for that one is the best ever! Or as Elon Musk often says "the best part is no part." He's invested tens of billions in a re-useable rockets with no landing legs because even if he doesn't know if it's gonna work, he's gonna spend billions to try and catch when they hover instead.

 

Did I not say "no car of mine or my family's that had EGR"?

A Gen 2 Prius does not.

 

I have had many cars from each decade since my first used 57 Plymouth for $75. Never had an egr problem until the 2012 Prius. I had a 67 Mercury that blew a hole in a piston somewhere between Toronto and Montreal but it still made it back to Texas. After that no major engine issues until the ill fated gen3.

 

Gen2 might not have a part called an EGR, but the valve timing acts as an EGR and that's the best design for an EGR I've heard of. Very few points of failure when it comes to that particular EGR design. Sad & stupid that the Prius design didn't get more sleek & simple over time, but got more bulky & complex. It was wrong to do that!

 

That's a misconception that's been discussed here before.

The valve timing of the Prius engine allows some intake charge to back up into the intake manifold.

Exhaust goes out the exhaust valves, and doesn't come back.

Corrected in post #29.

 

Some is better than none... And the emissions ratings of the first Gen2 proves it! A tiny bit less pollution from a EGRed Gen3 engine that blows a headgasket before 200K miles and burns oil from bad rings soon after is not an improvement, it's a design failure and a degradation of the original accomplishments of Prius simplicity.

 

My point exactly. Other than the size of my v, the 08 was a better car.

 

I stand corrected; yes, the Gen 1 and Gen 2 variable intake timing can be advanced as far as 18° BTDC on the exhaust stroke, so that a bit of exhaust gas does enter the intake manifold under some operating conditions, and they do even refer to that as "internal EGR" in the New Car Features manual. I thought I had seen otherwise in an earlier thread. Sorry about that.

Interestingly, they changed the range of timing adjustment between Gen 1 and Gen 2. The most advanced is the same 18° BTDC for both, so they can do the same amount of "internal EGR". They cut back on how far the timing can be retarded: in Gen 1, it could retard as far as 25° ATDC, but Gen 2 can only retard to 15° ATDC. I assume the 1NZ engine used in the c is similar, but I don't have its exact timing specs handy.

Of course the 2ZR-FXE engine used in Gen 3 also has variable valve timing and can do the same trick, even more so: the 2ZR's intake timing can advance as far as 29° BTDC. It can only retard to 12° ATDC. So they've restored some of the adjustment range they took away between Gen 1 and Gen 2: Gen 1 had a total range of 43°; Gen 2 trimmed that to 33°, all by reducing the amount of available retard by 10°, and Gen 3 expands the total range back to 41°, all added back on the side of advance (in fact, reducing possible retard by still 3 more degrees).

So Gen 3 is already able to do more "internal EGR" than Gen 1 or Gen 2, without its external EGR system.

So the added system must be serving one or more other purposes for them, like:

• Allowing them to decouple the amount of EGR from the intake valve timing. Maybe there are some driving conditions where they don't want the valves advanced that far, but still want to use EGR. That's not possible when it's only done by valve advance.
• Allowing them to used cooled EGR. Obviously the "internal EGR" is putting full fresh combustion-temperature exhaust back into the intake. Cooling the gas has benefits. A search for papers on "cooled EGR" turns up the research that was being done industry-wide showing why that's a good development.

 

Thanks, this is interesting information and most of the details I didn't know about... I suspect somewhere in these details is an explanation for why Toyota screwed up regarding combustion temperature which meant their ordinarily reliable engine for several hundred thousand miles can barely even get to 200K miles in a Gen3 without blowing a head gasket.

 

Phrasing it that way sounds like we know Toyota did screw up regarding combustion temperature, when to my knowledge any 2ZR head gasket concerns haven't yet been shown to be because of combustion temperature, much less the combustion temperature shown to result from a screw-up.

 

The screw up was acknowledged by Toyota in two ways. First in new piston and rings that can and were retrofitted into some gen3s and second by the wholesale reengineering of the 1.8 engine to make it reliable in 2016 through today's models.

 

How about an EGR design that can be close to 100% carbon choked by 150K.

 

Why is it every time we wonder about why Toyota severally failed engine reliability standards with the stupidity that is the Gen3 engine design that you're so eager to claim every possible explanation for what's caused early headgasket failure "haven't yet been shown to be" ?

You're like a broken record no matter how new or vague the speculation is? I clearly said "somewhere in these details is an explanation for why Toyota screwed up..." and speculated on combustion temperature out of respect for you being the only one who will say it's not because of a clogged EGR. Maybe rather than being dismissive of every single explanation that crosses your path you could actually simply type into google: "Why does a headgasket fail?"

The most popular answer that comes back is: "Head gasket failures are usually the result of engine overheating, so ensure coolant is topped up and the coolant system is in good working condition, with no leaks and an efficient radiator. A properly-installed head gasket will also prevent future damage" Head gasket guide – why does it fail and how can I tell? | RAC Drive

You informed us in your post: "Gen 3 also has variable valve timing and can do the same trick, even more so: the 2ZR's intake timing can advance as far as 29° BTDC. It can only retard to 12° ATDC. So they've restored some of the adjustment range they took away between Gen 1 and Gen 2."

Wouldn't that expansion of range put that engine at greater risk of running hot? And wouldn't an EGR that's clogged make it run even hotter? And wouldn't adding a different EGR system than Gen2 imply they were trying to lower combustion temperature more than valve timing can offer?

But go ahead and tell me all the magical ways we can't prove why the Gen3's premature engine failure because after 160 years of building internal combustion engines we still don't know why head gaskets fail?

Or maybe you could actually broaden the discussion with other possible explanations? That's all I'm looking for here...

 

A lower combustion temperature in an engine allows the fuel to burn cleaner and put less stress on the cylinder walls and head gasket so engine can be run at a higher pressure for a longer period of time.

An EGR valve lowers combustion temperature.

A clogged EGR fails to do that.

Most blown headgaskets are caused by engine overheating.

What is missing from this basic path of logic?

 

Ok, so take a moment and read what you just quoted. What does "overheating" mean in that passage?

In that passage, it means the temperature of the engine areas that are bathed in coolant. The EGR doesn't change those temperatures much. There is a whole cooling system and thermostat controlling those. Every time you accelerate or coast, or roll over an uphill to a downhill, you are affecting the heat load there more than the EGR does. And the cooling system has the capacity to take those changes in stride.

I don't know, got a temperature gauge on your OBD port? Why not look at it and see? Think you'd be able to tell your valve advance or EGR flow by looking there?

Lowering combustion temperature—peak combustion temperature—is one of the effects for which an EGR system can be selected. Whether engineers selected system B because they wanted that temp to be lower than system A could make it would be a question for the engineers, or for the research papers they were reading at the time. The ones that aren't paywalled for me probably aren't paywalled for you either.

It's good to note here that we've already changed what 'temperature' we are talking about; the peak combustion temperature is not the same thing as what the "most popular" head gasket result you quoted was talking about. When a person constructs an argument by starting with a source that uses a term one way, and then switching in the middle of the argument to a different meaning that isn't what the source was talking about, that's one of the classical holes in an argument.

You haven't got far to look for those. Take your same google search that you cherry-picked the "most popular answer" from (at least, you picked the "featured snippet" at the top of the list; have you checked with google on exactly what influences answers being featured snippets?). Scroll down and look at some others. Like here, a little further down the same search page:

· Overheating · Pre-ignition and detonation · Abrupt temperature changes · High mileage and age · Incorrect installation.

What Causes a Blown Head Gasket? – Becker Service Center

Ok, there's a source giving a few more possibilities than the one you happened to pick. It wasn't very hard to find. Out of those possibilities, which do you think will be most influenced by EGR function?

Here's a hint: what does the car's ECM do when it detects the EGR isn't functioning?

It retards the ignition timing, to reduce the likelihood of (wait for it) · Pre-ignition and detonation.

Are you really saying this is my first time to "broaden the discussion" this way? Maybe it would be fun to have a little betting pool on the exact number of older threads where I've been through this before.

That's not how proof works. It's not my job to tell you magical ways you can't prove something. The ways you can prove something are straightforward. Think you can prove a specific one of the known causes of head gasket failure is chiefly responsible for observed failures in Gen 3? Great! Determine what data and measurements you'd need to distinguish your cause from the others, collect and analyze, and show us how you did it. Or show somebody else who's done that already.

Supposing you prove that, think you can also pin that onto a "screw up" by the engineers? Great, maybe you can! That's a second step, though, and it would require pinning down what you think the "screw up" was, and showing it was something competent engineers would have seen as such at the time.

 

I don't own a garbage Gen3 Prius, nor do I want to study one... Every time I've worked on a Gen3 I've found all the design "improvements" to be incredibly incompetent and overly-complex. And newer Prius C, and Gen4 Prius have far less of that stupidity. It's totally insulting for Toyota reliability to turn into a gen3 that has multiple paths that lead to premature engine failure.

 

Well, consider it a thought experiment, then. Supposing you had a Gen 3 and a temperature gauge, and someone asked, "do you think you could tell your valve advance or EGR flow by looking there?", would you answer yes or no?

 

I’m pretty sure they did not redesign the engine ”to make it last longer”. They did it to pinch out even more MPG, even less emissions, make it even more lighter if anyhow possible etc etc. Like they did so many times before and keep on doing until ICE is phased out completely. If something is ditched out it’s because of developments that have produced better solution and that better solution may not have been available before. Manufacturers have technology roadmaps and whole lot of big and small incremental improvements in the pipeline and coming out continuously. While Gen3 engine may not have been perfect it certainly was step forward.

Funniest thing is the persistent idea that manufacturers want that things go broken so that people buy new (or buy parts). Trust me, they dont design something to go broken exactly at xxxkmiles or yyyyears. They have a target and improve as long as target is met. Sometimes target is met with wide margin, sometimes target is barely met. I guess Gen3 headgasket is the later Never seen a test spec stating ”must withstand x but no more than xx”.

 

Toyota often suggested their goal for each generation of Prius was to improve mpg by a significant amount. Risks were taken to achieve that goal.

To suggest Toyota is some kind of engineering superstar is believing marketing and not understanding engineering. All technical advancement, even at the best companies, is the result of thousands of compromises taken under a pressing schedule. At best it's three steps forward and one step back. Gen3 engine and hybrid designs were three steps forward and at least two expensive steps back.

Toyota paid for many new pistons and rings. Many more received new brake booster systems. They continue to pay for inverters. Accelerated life testing is never the same as years of use with tens of thousands of thermal cycles in wildly varying conditions. Gen4 and now gen5 benefitted from their gen3 predecessors.