ERG and EGR cooler question

I would say if you are going to clean your EGR valve and cooler and pipe for the first time to just do that , it took me 8 hrs to do mine for the first time ,I'm pretty sure if I had to do it again , I could cut some hours off . After ya get to know how to take the windshield wipers and the rest of the stuff off , it really isn't that bad doing it , the same with the undercover, but doing it the first time I would do one thing at a time unless you don't need your car for awhile.

 

What is an EGR "cooler"......and why would it be so expensive to replace......other than the dealer being a thief, that is ??

On most other cars, the EGR equipment is simple and relatively cheap and does not include a "cooler".

 

The piece referred to as a cooler is highlighted in yellow here:



At it's right side it connects to the exhaust manifold, and takes in exhaust gas when the EGR valve (bolted to it's left side) opens. The cooler has an internal "radiator", with engine coolant flowing through, to cool the exhaust gases.

The dealerships are not the the ones setting the prices I think. This online dealership signifincantly discounts the "suggested retail" prices for the valve and cooler (items 3 and 7), which are likely set by Toyota?

EGR System for 2010 Toyota Prius | McGeorge Toyota Parts

That said, I've heard of only one instance* here, where replacement of the valve or cooler was necessary, other than to expedite cleaning. The usual reason and method to get replacement valve and cooler is through EBay, used (for around $100~150 in total), and to pre-clean them to make the job go faster.

* Somebody recently fractured part of the EGR valve, trying to pull off the cylinder head while it still had one bolted connection. I'm not exactly sure how that would happen: if the EGR system is unbolted from the EGR "tube" and the exhaust manifold, I think it'll just come off with the cylinder head. But it happened, lol.

 

Thanks. I was seeing EGR but my brain was translating that to PCV.
It makes more sense to have some kind of cooler before dumping exhaust gas back into the maifold.

AND.....the one and only purpose of the EGR system is for pollution control.
So the point about the extended warranty on emission control parts maybe needs to be emphasized.
If you qualify for a free replacement under warranty, why bother to screw with it yourself ??

 

There are simpler EGR systems. I had apart a 2006 Civic Hybrid EGR component: it was just a valve bolted on a corner of the intake, about the size of your fist. Easily accessible too.

Not exactly: there's a sneaky secondary function: pumping exhaust gasses into the combustion chamber lowers temps somewhat, less oxygen to burn. Kinda like control rods on a nuclear reactor, lol? I think it allows the engine design to be a bit more efficient somehow, ultimately improve fuel economy.

And if it's clogging, combustion chamber temps go up, and head gaskets are more likely to fail.

Because Toyota still has their head in the sand on this. You will likely only qualify for replacement when the engine's in it's death throes. Most DIY'rs are seeing the "writing on the wall", pushing Toyota outa the way, and fixing things themselves.

 

I think they do this to minimize pollutants as well, specifically NOx.

 

Yes.

 

I don't think Toyota thought it would need maintenance as it clearly does...probably why it was poorly located.

 

Just stumbled on this, some info on the 4th gen EGR revisions, which maybe gives clues to what's inadequate with 3rd gen:

4th-Generation Toyota Prius Teardown (Part 1) - MarkLines Automotive Industry Portal

Think it's been linked before?

 

Interesting read. They're actually increasing the volume of EGR (doesn't say how much). Plus that water jacket spacer with rubber at the bottom of the cylinder bore to allow increased cooling at the top. They say it lessens knock. They don't don't say it lessens head gasket failures. Out loud at least.

 

Hope that spacer is stable in the long term, doesn't start to come apart. Ever.

 

EGR was invented over 40 years ago to reduce NOx emissions. Soon thereafter, manufacturers (starting with Nissan, if I recall correctly) began taking advantage of the consequent reduced throttling loss to improve fuel consumption. Toyota takes full advantage of that idea in the Prius.

Considering how so many engines have lived long lives with little or no EGR, I'm a bit skeptical of the notion that EGR is necessary to avoid excessive temperature. Better or more detailed explanation is needed.

 

I agree. However, if you are forced to use it for emissions reasons, why not try to make it work in your favor if you can? I know I would if I were an engine designer. Given a choice, engine designers would likely rip that stuff off their engines. You don't see it on racing engines unless the series spec requires emissions limits.

 

The sense I get is that EGR is primarily there for reduced tailpipe emissions, but it does also reduce the combustion chamber temps. So the engineers took advantage of that in their engine design; they're counting on that. And then when it clogs, the fun begins.

 

Clearly they aren't doubling down on EGR volume just for the sake of NOx at this point. (It's funny that no Prii are reported failing emissions tests even with all those very clogged coolers out there.) So the increase is for either fuel efficiency or the cooler cylinder temps or both.

But if adequate EGR flow is necessary for 2ZR-FXE engine health, it's a design flaw that there's no detection of the flow's sufficiency before it's too late. Nor of the apparently critical rise in engine temps resulting. (On top of the flaw that causes the clogging to begin with, and the flaw that causes partial clogging to unevenly distribute EGR per cylinder .) Yet the result is apparently a blown head gasket, which falls to the customer. Whereas a detected faulty EGR condition might be covered by warranty in CARB states for example. Hmmmm.

 

There a code that can be triggered, for insufficient EGR flow, but it seems to need near 100% blockage before it'll trigger.

 

OK, a couple of back-to-basics questions:
1. Has it been proven that head gaskets will not fail if EGR is kept clear of clogging? Critic's example seemed to call that assumption into question. Correlation is not causation.
2. Is the system programmed to maintain significant EGR flow even when maximum torque is demanded (which occurs at 4000 rpm, according to the "operating line" Toyota published) or maximum power is?

 

2. I don't think so. I recall a member here who monitored their EGR valve with a third party tool and saw that the valve opens the most as you're accelerating the least. So when the engine isn't working hard, the EGR comes in to help cool it. When you're making the engine work, the EGR let's it do it's thing.

 

As a mere "wise fool" myself when it comes to engines, I can only remain agnostic but interested regarding the causes of 3rd gen Prius' clearly high rate of early HG failure. There was that one before 100K, I don't even know if that one was burning oil yet. I'm hoping clarity arises eventually. (But I'm all for cleaning those EGR coolers in the mean time!)

What I see on my 2010 using a cheap OBD2 adapter and the Torque app confirms Wikipedia's description of EGR implementation:
EGR cuts out at idle and at full throttle by design. Commanded EGR increases steadily as demand (per the HSI) increases, reaching (for me) just over 60% before the high demand causes it to cut out entirely. And resuming again in proportion to demand that is within some operating range.

I did play with logging RPM and EGR and poked at it with Neanderthal level Excel skills. I came away with the impression that RPM alone was not the sole determinant of commanded EGR, but it's a quick and dirty proxy for "engine load" or whatever actually maps to commanded EGR. Here's a snippet from a throttle pulse just for grins:

A whole log is attached if you want to get a better feel for how EGR and RPM tend to relate. This one doesn't show the high RPM cutoff of EGR, sorry. But you can infer that cruising on the freeway at 70mph for hours is likely to command a large and continuous amount of EGR, even if drag racing a 1/4 mile doesn't.

 

I'm from the "that can't be good" school of thought: if Toyota provides passageways and they've been near-completely clogged...?