Verification of EGR cleaning

Googling this:

How much carbon coating on egr cooler fins is needed to impact cooling ability

the AI summary is interesting.

 

Is our primary concern, temperature or flow of the exhaust gases re-entering the intake manifold?

 

Both? The cooler is quite the contraption.

 

I generally agree, but since one version is so much easier (no vowel) and still delivers above 21 kPa flow, it’s still relevant.

The cooler will look terrible even if brand new, after some hours of engine running. That does not really indicate a bad flow…

I have still failed to see any validation data of actual flow thru this cooler. This is likely why Toyota prefers blowing it with pressured air, since it will indicate flow exist - if the back is removed (I did not remove the back of the cooler since those bolts require wiper/cowel removal. So much ash blew out in the front (use mask)).

Why are the exhaust gases cooled? Likely engineering explanations are due to the manifold is plastic, the delta between normal airflow temperature (hundreds of degrees difference) is very big, and with g3 this was a new tech. How do newer EGR treat this..? This is like a beta/alpha version in my analysis.

The trick to block the throughput at the pipe is very smart and is done by Toyota to separate the vibration issue (my plug-in had massive vibrations at 30-60 kmh when car was bought at 270.000km) from the lovely head gasket issue.

 

This is true, but the super small passages of the manifold are much worse in that regard (again, since they can have added oil. This does/should not exist in the cooler environment (normally)).

 

How many hours do you think?

 

One?

 

I wish I had checked the non-continous EGR monitor flow value before cleaning, would have be interesting.

My plug in 2013 had no codes or indication of issue in the ECU, but the engine behaved very bad with morning rattle and massive vibrations when engaged at all speeds. All gone.

Cheers to @Mendel Leisk and priuschat alumni - and YT folks (merv et al) helping!

 

I'm not sure what you're getting at here. The car does a flow test routinely, and you can query for the most recent result at any time.

Has Toyota expressed such a preference? I didn't think they had said much about cleaning the thing at all.

I don't think it was such a new tech really; cooled EGR was being researched industry-wide, and gen 3 was when Toyota got around to adding it to the Prius.

Industry publications like this one suggest that volumetric efficiency was a main attraction:

Gasoline engine exhaust gas recirculation – A review

Hot EGR mixing with the intake air heats that too, decreasing its density, so you get even less of it into the cylinder per stroke; you'd need a bigger-displacement engine to get the same power as one with cooled EGR.

That's what I take away from reading the abstract and section snippets of that paper; I might have access to the full text through my organization but haven't checked that yet.

 

I work at that kind of organization. Here it is attached as PDF in full. Science should be public domain…

European Union (Gasoline): EOBD (European On-Board Diagnostics), which monitors emission control systems including EGR, was made mandatory for all new gasoline vehicles sold in the EU starting in the 2001 model year.
​

Fascinating Prius 1-2 avoided this due to the hybrid concept.

ATTACHMENT Copyright © 2025 Elsevier B.V., its licensors, and contributors. All rights are reserved, including those for text and data mining, AI training, and similar technologies. For all open access content, the relevant licensing terms apply

 

As you recently stated, this flow is measured at the MAP sensor. There are many passages afore, so it’s not a measurement of actual cooler flow?

Has Toyota expressed such a preference? I didn't think they had said much about cleaning the thing at all.

That is, in an interpretation, an indication of Toyotas preference to ignore it as a culprit. But indirect knowledge via my Toyota source and TCCN indicates they instructed about blowing it out.

I don't think it was such a new tech really; cooled EGR was being researched industry-wide, and gen 3 was when Toyota got around to adding it to the Prius.

True indeed, and also validates my point it’s a beta test for Toyota, as they were forced to introduce it and did it not ideally due to lack of experience.

 

All Toyota had to do was run a few pre-production gen 3's around a track for 200k miles, and we wouldn't be where we are, with clogged EGR, blown head gaskets and runaway oil consumption (the latter largely due to to the low-tension piston rings they spec'd, till sometime in 2014 model year).

Like any corporation, their public statements are VERY terse and guarded. There's no way they're going to recommend any sort of preemptive EGR cleaning; they'd rather turn their backs on the dumpster fire of blown head gaskets.

What's the kilometers on yours? I seem to recall reading 270k kms somewhere, and it's a relatively recent acquisition?

 

The test result is a pressure delta between when the EGR valve isn't open and when it is. There isn't anything to account for the pressure change except EGR flow.

The "many passages afore" are a fully series path, except for the four manifold passages in parallel.

Therefore, clogging anywhere (including the cooler) could cause a bad result. The only place there could be clogging consistent with a good result would be in some subset of the parallel manifold passages (which is why it's extra important to check those directly). Flow through the cooler is confirmed by a good result.

Out of curiosity, what's that a quote from? Didn't find it in the PDF attached with that post.

 

See post #30 for the PDF.

 

I saw post #30 for the PDF. Did I forget to mention that PDF doesn't seem to contain that quote?

When you search that PDF, can you find that quote? If so, what page is it on?

 

You are right. The statement is not part of the PDF (which is a peer reviewed article). The statement's source is probably one of the EU directives. I could not find direct source. But I bet @priumium can.

 

@ChapmanF With an active valve test in techstream you can test the valve potential clogging effect (or malfunction) on the pressure, it’s in the repair manual attached above.

I like this test more compared to looking only at flow monitor pressure. You can open and close the valve on demand with this test, as such indicating initial blockage before manifold.

The test result is a pressure delta between when the EGR valve isn't open and when it is. There isn't anything to account for the pressure change except EGR flow

That’s the active test in TS you are now referring to, and not the monitoring value, right…?
—

The EOBD quote is is not from the pdf, but from other sources, attached. It’s mainly OBD mandatory, so the EGR is part of a UN instruction.

As mentioned, the vehicle type that required EGR is M1 and below - which does not include the Prius, attached pdf of this definition.

 

You are correct of the km ODO. Bought this 2013 model year this summer. According to Toyota this model has the software update and… not any other updated parts.

The valve was replaced 2020 according to service history. It was likely ok, a bit of ash but not an issue. My manifold though was fully clogged with oily ash, and after I cleaned it with brushes, hot water and pine oil soap it has no vibration or severe morning rattle. I never had any misfires at all detected before this.

(I also heard several Toyotas service personel mention they do believe this EGR fault indirectly is one culprit of the head gasket issue, which indicated the cooler does not cool enough when the entire system is clogged, and hence introduces a higher temperature to the combustion chamber than anticipated…

Atleast part of the issue is the aluminium and the coated gasket expand at different temperatures and the coating gets destroyed by this minuscule thermal movement.

 

This is an interesting thread.
How does a Toyota service dept. test that an EGR is clogged or getting clogged?
Are there preventative procedures, other than part removal?
(FYI 2017 Prius V)

 

They block the pipe from the valve and check for effects missing, such as vibration. This concept is Toyota officially sanctioned internally, as proven in the below video and on my used car`s documented service history, where this blocking was done and proved the EGR was causing previous customer issues (they then replaced the valve, but nothing else).

Check out this very informative TCCN video, Toyota did thousands of these TSB fixes when current.

As for the topic of preventive measures, I have failed to find or even see anything directly relevant DIY to prevent this issue. It’s just a bad engineering design, that was fixed for G4.

Analysis I did as DIY is checking the pipe (easily removed) and it was not clean. It was not clogged. But indeed; This indicates the next part (manifold) is very much not clean at all.