Is Head Gasket failure common in Gen 3?

I'm not trying to be a smart aleck here, but how would puddles in the bottom of the intake manifold flow up against gravity and into the cylinder? And if the answer is from the flow of the intake air, then how is it that the puddles form in the first place? If the flow of air is sufficient to pull standing fluid uphill, then no liquid could possibly ever condense and pool in the intake. Any trace fluids deposited in the intake while running would immediately be drawn into the cylinders and burned, therefore never allowing any to accumulate and pool.
Or maybe I'm looking at it all wrong.

 

The oil is getting sucked in from the PCV valve while the engine in running, of course.
But you shut off the car, the oil that is in there, and in the air, settles to the bottom.
Over time, it builds up.

 

Understood.

But how would pooled fluid in the bottom of the intake make it's way up into the cylinders?

 

Air flowing over it, quickly sucks it up little by little. The more that's in their, the higher it gets,
more chance of covering the sensor, causing inaccurate readings....

 

The ports seem to spit out a little oil too, due to the Atkinson cycle engine? I removed the intake port, about a week after a cleaning, and there was an oil tear drop under each intake port.

Coming up on two years since OCC install, last time I looked with the throttle body lifted off, no pool, but a sheen. I would attribute that to a combo of slight amount making past the OCC plus the spit-back from the ports above.

 

I’m with you on that too. What I’m questioning is the assertion that pooling oil in the intake manifold is causing oil to then pool in the cylinder(s), causing knocking at startup.

 

Maybe the oil pooling in the intake manifold is just the tip-of-iceberg, and there's a lot of oil that stays in air-suspension, goes through to the intake manifold?

Which then combusts and clogs up the EGR.

Which causes the engine to run hotter.

Which causes head gasket failure, coolant going where it's not supposed to, hydro-lock.

 

I cleaned my egr system around 120,000 and the cooler wasn't clogged at all. It was very sooty though.
Nothing had heavy build up, but the intake did have some oil at the bottom.
The previous owners drive a lot of highway miles at 65mph.
I think city driving causes more of a build up because oil has more time to pool.
At highway speeds you have that constant flow and it burns off.
But driving too fast causes oil burning.

 

But how did it get to the ports? Via bad rings, bad valve stem seals or from the manifold or ___ ?

 

Don't know. Oil does not drop a discernible amount between changes. I think I've heard it had something to do with Atkinson cycle??

 

EGR is used to meter exhaust gas back to the intake to reduce the amount of oxygen -> reduce the amount of fuel and power.

If it is clogged and the engine computer isn't aware of it, it will use more fresh air for combustion (more oxygen, running leaner). Running with more oxygen and leaner means a higher chance of knock / detonation.

Maybe knock and detonation is what kills the gasket and piston / rod?

 

@mjoo says properly functioning EGR is also necessary to keep combustion chamber temperature down. Raised temperatures mean lots of things, maybe more differential expansion of metals, also stressing head gaskets?

One specific thing that can kill piston/rod is if the head gasket fails so that coolant starts leaking into the combustion chamber: if enough gets in there, it will stop the piston's upward travel (since coolant can't compress), and then the piston rod bends. It's referred to as "hydro-lock".

 

EGR brings down the combustion temperature. Cooled EGR brings the intake gas temperature down to improve the thermodynamic efficiency of the engine. No EGR raises the partial pressures of Oxygen and fuel. That causes the combustion chamber temperature to rise, which increases the exhaust gas temperature. A hot engine is likely to output more NOx. The heat also causes head gaskets to turn brittle. Then they crack and fail.

A little history of smog controls: The first attempts at reducing smog aimed at reducing hydrocarbon emissions. That entailed sealing off the fuel system and the engine crankcase. To prevent overpressure in the crankcase the Positive Crankcase Ventilation (PCV) valve was invented. Instead of making smog better it got worse. The culprit was NOx. Combustion temperatures had increased and NOx emissions increased. As a side note here, there was a problem at the time with damage to heads, exhaust manifolds, and the gaskets due to the higher temperatures. About 1970, EGR was introduced to drop the combustion temperatures to reduce the NOx emissions. People complained in the early 1970s about EGR smog controls killing performance, but it also increased the engine lifetimes by reducing the combustion and exhaust temperatures. I have seen what high exhaust temperatures can do to an exhaust manifold. Once they turn brittle, you can shatter the metal just by tapping it with a screw driver.

Today's exhaust manifolds and exhaust manifold gaskets are made of better stuff due to the history fried exhausts. The head gasket failures are probably not something that Toyota anticipated. But I think they knew that the Atkinson cycle throws of lots of carbon, because they put an over-capacity catalyst on the exhaust. That is what attracts the thieves to our cats.

I postulate, but do not know, that as the EGR plugs up and the temperatures increase, the carbon fouling also increases. So you get a run away effect.

 

Too, PCV valve that keeps chugaluging oil/water/gas detritus into the intake can't be helping the carbon build-up situation.

 

I agree! There is something wrong with the way the PCV valve works on these engines. Normally you see oil intrusion like that when the PCV valve has failed, but this car has oil in the intake that is way over the top.

 

How does that explain the ones that consume very little oil, including mine so far?

 

Isn't that because Prius use slightly less then the amount of motor oil that used in a regular car and people over fill the crankcase with too much oil?

 

I have no idea what that means, lol.

I see no appreciable drop in dipstick level between changes, and drain my OCC at the same time. Through winter it collects the most, maybe 100 cc in total, but maybe half oil, half water.

 

When you add too much oil and your dipstick indicates that your oil level is higher than full your PCV gets messed up up because of too much extra oil. How could you not know what that means?

 

I'm currently changing oil on a pilot, a cx-5 and my Prius. They're all 4.something liters, and I manage to put the specd amount in each, somehow.

I don't overfill the Prius, and the OCC still manages to collect 100 cc every winter (oil/water mix), and about half that amount through summer.(mostly oil).