How many miles on your Gen 3 and what Repairs / Maintenance have you done?

I wonder how much that carbon-encrusted radiator was cooling?

 

Another interesting empirical question.

 

What if that 20k miles were 98% highway miles, say 400 miles per day?
And the oil did not 'look' bad.
And a proper oil analysis showed that all was well using this oil change interval?
Science!

 

This is great to hear about your Prius.
And no EGR cleaning, correct?
Very encouraging !!
Keep us informed, please.

 

No, No, No! You MUST change your engine oil every 3k or you will burn oil, contaminate your cat, screw up your rings, block your EGR and blow your headgasket.

It's OK to NEVER change your transmission fluid because Toyota says so even though they clearly have no idea what they're talking about recommending a 10k engine oil change interval.

Screw your data. Only feelings and speculation are allowed here

 

How did you measure how clogged those other dozen were, to serve as comparison benchmarks?

 

Just the amount of light compared to a new EGR cooler. To be clear I have been talking about the cooler not the valve.
No way to benchmark my results do to no exact measurement taken.

 

@mjoo tested water flow rates, before and after cleaning. Say pour in a cup, see how long it takes to get through. If you start pouring it in, and it's coming out a drop at a time, guess that's pretty clogged?

 

That would be a start on a method. Throw in a known height for the head of water, a measuring cup, a stopwatch, and baseline measurements of clean ones, and it would be a lot like a method. Similar thing done with air might be slightly better, avoid having to reason about how water flow might be different.

Without something like that (or the flow test the car does on its own), it's almost better for people to stick to saying stuff like "looked pretty clogged" rather than "95% blocked", as the latter implies something's been quantified to that degree of precision.

 

Here is a photo. You can use your judgment.

 

That's 94.5% at best

 

You have the same eye calibration as me. Lol

 

Three significant figures! Hire that one.

 

EGR wasn’t cleaned prior to Headgasket. I did get a cleaned out egr valve while I replaced my headgasket

 

But it's the EGR cooler and the intake EGR passages that are the choke point.
Supposedly the system will give a code when the clogging gets to a certain point.
Something about MAF, MAP and EGR valve position not creating the expected MAP number....

 

It's not really that complicated. The engine intake sucks the manifold absolute pressure (MAP) to a value below atmospheric. Opening the EGR valve lets more gases into the manifold, so the MAP goes back up some (unless the EGR system is completely clogged, in which case it would have no effect on the MAP).

The car periodically does exactly that, under specific conditions. When you are decelerating with a warm engine above certain speeds, the car will open the EGR valve a certain amount and see how much the MAP goes up. That number is your EGR flow score and higher is better. Freshly cleaned tends to be around 21 or 22 kPa.

If you use a scan tool and look at your last score, you'll also see what the car considers the 'min' value, where P0401 will be set if the score ever gets that low. But if you feel like being proactive, you can choose your own 'min' value and decide to clean the system when it gets to that point, instead of waiting to hit the programmed min value and get the code. For example, I cleaned mine when it got down close to 10 kPa, still a long way from setting a P0401.

 

One thing: MAP sensor is upstream of the small diameter EGR passages, one per intake port, and those passages tend to clog unevenly: cylinder one clogging first, then two, and so on.

I think Toyota saw this happening, and that precipitated their revision to the passages. Not sure how much that revision improved things. Uniform clogging would be "optimum".

 

That, and anyway there are four of those and only one MAP sensor, so no matter where it was located it wouldn't be able to tell you about those passages clogging unevenly. It can only detect the overall flow.

That's why I've been recommending, in addition to watching the car's computed score for overall flow, also taking the manifold off from time to time for a look at those passages. The manifold by itself is a quick easy job, no evil studs, no dealing with coolant, etc.