2011 Prius Head Gasket Failure

From the diff'rent strokes department ... I left the stud in place. I didn't find it much complicated extricating the cooler, and I even kind of liked having it there later to hang the cooler on while lining stuff back up. Mostly what I liked was just letting it be one thing I didn't have to fuss with.

 

You never miss an opportunity.

 

I would recommend that the EGR cooler be cleaned long before 179k. OP waited far too long.

 

That is a theory.
Has there been any way to prove it?

The Prius engine is a Pseudo-Atkinson cycle engine. With the variable intake valve timing it can effectively control
the compression ration.
It's has a high compression ratio number, but does not operate that way. It does not require high octane fuel.
(I suspect because of this it may not lose as much power at high elevations, to a point, compared to normal engines.)

With all the various sensors this engine has it should not run itself into 'self destruct' mode. That's the theory, correct?
In fact it has a pressure sensor in the intake to determine if the requested EGR amount is doing its job, correct?
And it will throw a code if there is a problem, correct?

You'd think if 'Periodic EGR system cleaning' is a vital service, and would allow the engine to go beyond its typical Head Gasket Failure mileage,,
Shouldn't Toyota point this out SOMEWHERE in some service manual?

Do other Toyota engines have similar failure time frames?

 

To present an opposing view?
I'm waiting for your expression to change from the differing opinions on this subject.

I have experience with high mileage Gen3's. I'm not making this 'stuff' up....

 

Now this sounds like a really good scientific test! No faith required.

For the skeptics who don't want to tear into cleaning an EGR system, that might or might not help with engine longevity.
It would also be an excellent 'before - after' cleaning test!
If your numbers above ^ are typical, the EGR system is flowing and no service is needed, correct?

 

I agree that the claimed EGR -> head gasket causality is speculative, and that its proponents are relying on some points that make it possible or maybe plausible, but haven't shown much interest in the kind of evidence and analysis that could establish it, and continue to oversell the certainty of it.

I did swap my valve and cooler over the summer, more as a Pascal's-wager exercise than because I'm super convinced of the connection. My old valve and cooler are still sitting here in their exact as-removed condition, waiting for me to devise a good quantifiable way to bench flow test them and then do that before and after cleaning them. When I find the round tuits I'll post the results.

After I posted the above about the active test opening the valve several steps, I found an even easier quick check, where you just ask the ECM what the result was the last time it ran its own self test of EGR flow. Those numbers are easy-ish to compare; they wander around a bit, but mine did go from 10.xx to 21.xx the day I did my Pascal's-wager valve and cooler job. (Higher numbers are more flow.) That's more than their normal wandering around. Whether the scale is linear (does 10.xx mean half the flow of 21.xx?) is another question, one of the reasons I want to bench-test these parts I removed.

The suggestion I would probably choose to leave with people is to pull up that test number now and then to have an idea of the overall flow, plus actually removing the intake manifold now and then (a comparatively easy job) to check for clogging of its four small EGR passages.

The manifold is where the one EGR path splits into four, and because there is only one MAP sensor, the overall flow self-test done by the ECM doesn't reveal what is happening there. If the passages are clogged to different degrees, it is possible that an "OK" overall flow reading means "more than OK" EGR into some cylinders, (un)balanced with "less than OK" EGR into others, and out of all the PriusChat-proposed mechanisms linking EGR to engine damage, that right there is the one I would give the highest score for persuasiveness.

I did the check of my manifold earlier, more like a year and a half ago.

 

Regarding the MAP sensor:

1. There seem to be two styles. My (2010) sensor has a small plastic cage, and what looks like some sort of resistor within it. I've seen another locally, where there didn't seem to be anything to speak of in the cage.

2. First time I checked mine it was practically swimming in oil, mostly delivered by the PCV circuit I'd speculate, and some spit-back from the intake ports. I wonder if that effects it's reading.

And as you say, if one of the capillary EGR passages, say at cylinder #1, is near-totally clogged with carbon, ahead of the other 3...

 

The ones with the red doodad have the -52010 part number:



The ones without the doodad have the -47010 part number:



The different part numbers were mentioned here and Elektroingenieur looked into the details here. It seems the doodad-positive ones were used in some of the very earliest production months of 2010 Gen 3, and the doodad-negative ones have been used ever since. Neither one is listed as a substitute for the other, so presumably whichever type the car came with should be used if replacing it. The doodad adds about $34 to the part.

I don't think there's much to go wrong with the MAP reading. You can always read it with the engine off and compare it to your barometer (or the pressure reported on your local weather web site), or with the engine at idle, where it'll be lower, typically around 4 psi.

 

This situation is plausible.
But what would the effect on this 'cylinder #1' be? Slightly higher combustion pressures than the other 3?
And this stresses the head gasket in particular?
But this higher combustion pressure is not creating a 'knock', so the knock sensor is not doing its part to protect the engine?

 

Well, a loss or reduction in EGR flow to a cylinder should result in higher combustion temperatures and pressures. I would think that if things reach the point of detonation the ECM SHOULD see this on the knock sensor and retard timing. That's why it exists. Should be easy to check scan data and see if there's any knock retard or some such.

An experiment to run would be to (securely) restrict or plug one EGR port in the intake then drive and record scan data.

Posted via the PriusChat mobile app.

 

@Mendel
Thanks for the tips. i wont be doing it by myself. I would like to but i dont have heated garage and its 0deg celcius outside. I know the mechanic very well and i’ll let him know. We’ve already exchanged some message. Pcv valve going to be changed also. Bought oem valve

 

As far as I can see, most of the vague allusions to "increasing the pressure" or "increasing the temperature" in this connection are hot air. The effect of the EGR is (confirmedly, it's the reason it's used) to make the combustion temperature and pressure curve wider and less tall/steep; the area beneath it is the total heat released and of course is the same (if it weren't, you'd be leaving MPGs on the table). On the macro scale, the temperature is under control of the cooling system and thermostat, which are up to the job. Differences in peak pressures and temperatures are matters of milliseconds, and while we know there is enough of a difference to reduce NOx (again there's no controversy on that point, it's why it's used), I've seen nothing presented here to suggest the difference is relevant to head gasket longevity, and I've been unable to find any on my own.

The matter of detonation is a little different story. While you could describe detonation with phrases like "higher combustion pressures" or temperatures, it's in kind of a class by itself on those measures. And unlike the dearth of literature describing problems with insufficient EGR simply through increased temperature or pressure in the usual ranges, there is easily found literature about detonation being a cause of engine damage, and of it being a possible result of insufficient EGR undetected by the engine controls.

When ECMs detect insufficient EGR flow, they proactively operate the engine under fail-safe adjustments (less ignition advance, for example). Perhaps they could rely on the knock sensor for this but they don't; maybe it's like, I don't know, getting a cheap vaccine rather than waiting to get sick and getting a $2,100 monoclonal antibody treatment. When the ECM has reported P0401 or P0403, it already is operating the engine more cautiously.

The possible concern, then, with uneven intake manifold clogging, is that the ECM may still think the flow is Just Fine. That means not only that some cylinders may be getting too little EGR, but for the flow to be Just Fine, the others are also getting too much. The ones with too little may be at risk of detonation; the ones with too much may be at risk of misfire, not as violent but definitely not great for the engine (or the torque damper, or the cat).

There are occasional posts where people see OK at idle and OK at full throttle but lousy running at mid loads (where the EGR is used); as far as I can see, that is pretty much always a sign that the valve works and there is overall EGR flow (otherwise there would be nothing to cause the effect), but that it is not reaching the cylinders fairly, so seems to me like a pretty clear finger that points at the manifold whenever I hear it.

 

At full throttle, the EGR on this engine is supposed to provide 21 % dilution of the air-fuel mixture in the intake manifold. If the EGR is plugged, you have the inverse math of that ratio showing that you have 127 % of the maximum air-fuel mixture going into the engine. While you do not normally run the engine at full throttle all the time, with the EGR plugged up you adding to the heat load on the cooling system. And the short block was originally designed for a 1.5 L engine. With it bored out to increase the displacement, it is reducing the engineering margins built in by the designer of the block.

You also see similar head gasket failures on this engine when the water pump fails.

In both cases you have heat as a common cause. This engine has steel bolts holding an aluminum head. Aluminum expands at a higher rate than steel. The head gasket then gets crushed and released by the expanding and contracting aluminum head over multiple cycles of heating and cooling. Eventually you have a leak.

 

My understanding was that at full throttle, the EGR on this engine is to provide 0% EGR. Is your information different? Can you share the source?

 

This is true.
And it's also true on most modern engines (aluminum head and block).

The question is, why does the head gasket fail like clockwork on the Prius engine?
Doing all the work to keep you EGR circuit shiny clean does not seem to help with this head gasket problem when you have +200k miles.

It is definitely the weak link of having a high mileage Prius.
It's why I quickly bailed out of owning one, plus I wanted to move on up the tech ladder to a BEV.

 

Late last winter here, a local Priuschat member took on the EGR cleaning, and I dropped in on him: he was doing it in his driveway, sunny day but just around freezing. I didn't stick around too long; too cold for me. Good summer project.

 

@ASRDogman might argue that.

A common theme seems to be "fools paradise" for the first 150K miles or so, then when symptoms start cropping up they get on making things "shiny clean", too late.

 

Now if the results were only quantifiable.

That test listed above about operating the EGR through the OBD-II sounds promising!!
It would be a good 'before / after' test to see if anything changed.

 

I'd argue the same.

Our old 2010 is still alive and kickin' with over 215 k miles now (at last report from @Pedal Logic as he knows the current owner) and the head gasket is still in tact. EGR circuit maintenance performed at 120k and about 177k miles.

Do the complete circuit early (around the spark plug change at 120k miles) and it should help.