Knocking sound, rod bearing or torque converter etc.

My 2 cents: it’s typically head gasket failure, caused by EGR clogging. Cleaning the EGR system is always good, but overdue, won’t “reverse” the head gasket failure.

 

Egr cooler replaced and egr valve for $1k installed - manifold extra. Still won't fix it. Head gasket.

 

No oil, just carbon (aka soot). It also deposits lots of carbon along the way, in the EGR cooler/valve/pipe, intake manifold EGR passages and intake ports in the cylinder head. Any oil you see is due to the PCV system.

Coming into the EGR system? Just possibly more soot, though copious amounts of soot can collect without the engine consuming oil. So I'd say no, the piston rings are not the only reason the exhaust is sooty, that's just the nature of exhaust.

And again, think it through: how do you picture oil making it through the combustion chambers, without burning? They don't call them "combustion" chambers for nothing.

Sentence fragment. Again, just soot.

You're getting warm. But speaking of warm, I think that uneven build-up of soot on the EGR passages in the intake manifold causes the cylinder head to get warmer, asymetrically, with cylinder one end heating up sooner. And that end is where the head gasket starts leaking coolant into the cylinders. And that coolant causes knocking sound, pistons struggling against coolant, crankshaft fighting the damper between engine and transaxle.

Too, as soon as the EGR cooler gets a decent coating of soot, does this reduce it's reason for existing, namely cooling? Does the soot insulate the fins? I'm thinking it can't help.

The "school of thought" proposing to not "fuss" with cleaning till the Techstream reported flow rates are significantly dropped doesn't seem to consider this: the gas may still be flowing "ok", but it's temp is higher?

See previous.

@ChapmanF should be along shortly to clean up after me.

Disclaimer: the above may be a little over the top; I had coffee with my pancakes this morning.

 

Cliff notes version

1) this 2010-2015 naturally passes oil and carbon thru the EGR system to the cylinders

10-14 have screwed up rings that clog and fail to flex usually after 125k miles. This starts blowby and oil consumption with thick carbon everywhere.

2) as engine ages and piston rings loosen up the amount of oil , water vapor and Carbon increases and cause
a) increased pressure in the cylinder which stresses the head gasket and
b) deposits of oil and carbon crud on the walls of all the egr and intake manifold components.

Rings stick not loosen

3) the uneven buildup in the intake manifold in particular causes uneven combustion which causes the knocking (as well as extra ordinary pressure on the head gasket).

Carbon build up causes pinging which is worse under load. Knock sensor adjusts but clean engine does not have knocking at first.

4) the crud buildup in the cooler, egr valve and pipe slow down and cause condensation of the vapors that would otherwise quickly flow through to the combustion chamber and be burned .

Redundant and not a big issue.

Issues:

A. Bad ring design
B. 10k mile oil changes stretch to 15k
C. Bad egr design with intake before cat
D. Oil burning and thick carbon by 175k sometimes 125k
E. Bad cylinder cooling design
F. Uneven cylinder cooling
G. Large thermal cycling with engine idling or stop and go
H. Narrow head gasket width between cylinder and not enough black sealant coating
I. Likely bad water pump speed control software not updated on most 10-14 ecus.
J. Same ecu update improved egr valve logic

*All changed in gen4 and B becomes a non factor*

Once a very small coolant leak starts, a plug gets fouled overnight by cooling system pressure.

Engine starts and misfire causes transaxle damper to slip causing ‘rod’ mechanical noise typically misdiagnosed by mechanics unless familiar with Prius hg symptoms.

Engine burns off fouling coolant and runs fine. Early on the hg leak is sealed quickly as the engine runs and warms up. Maybe does not repeat for days or weeks.

Gets progressively worse leak such that late stage it happens every day and then every engine off on at lights etc. Coolant drops noticeably.

Turn off the lights the party is over.

 

"Preliminary Conclusion , plugs were bad."
That's funny!

Next step:
Replace head gasket.....

Do a pressure text, I'd bet you'd find coolant leaking into the #1 and #2 cylinders...

 

The P0301 does just broadly indicate a misfire for any of the possible reasons, but the P035x codes do suggest there was something to do with the ignition system.

 

New plugs often burns off the coolant fast for a week or two.