Information on EGR system and intake Manifold Cleaning

There are a lot of different cap sizes, so you have to find one that fits

 

Fits the reservoir cap I suppose, since there is no cap on the radiator.

 

Update: Prius back on the road with all systems functional and more power than recent memory. Endoscope investigation of cylinders didn't reveal any obvious leakage but seemed fairly inconclusive. Tracked misfire down to bad coil in cylinder 4. Moved to cylinder 2 and misfires followed coil. Replaced coils in #3 and #4 with two new coils ordered online here via Amazon.ca for CAD $91 each (vs CAD$191 at Toyota). Immediately took care of the problem.

Many thanks for your advice throughout the process., Mendel and Mr. Dogman... would have been lost without you. I received the card below from my 11yo daughter in the evening, along with various gifts from my wife in appreciation. They really know me too well.

 

Nifty! I hope that resolves your issues.
Keep an eye on the coolant level. And be alert to cold start engine rattle. Also after driving and
the car sits for 30 minutes or so, it may rattle. That was my first rattle. Coolant seemed to be where
it should be. But the next day, same thing, this time the coolant was slightly lower. The mark is
right on the seem. I now keep it slighty higher.
I had planed on changing the head gasket in the next few weeks, but it decided it was time,
at 301,xxx miles.....

 

I'll keep an eye on the coolant over the next few weeks and months for sure. What causes the rattles due to gasket failure? Is it misfires due to incursion of coolant? Or?
I'll attach the endoscope images taken inside the cylinders but I can't seem to download them at present.

 

Coolant in the combustion chamber is hard to compress, and maybe fouls the spark plug as well. I think the sound is mostly at the damper between engine and transaxle, but not sure. The engine's not happy, that's for sure.

 

It’s coolant fouling of the plug causing misfires for 5-10 seconds. The engine loses sync with the transaxles motors causing a friction damper between them to severely rattle. It also causes the engine to shake. Left too long and you bend rods and blow holes in the block.

 

When the engine is hot, the gasket seems to seal. But when it cools down,
coolant will leak into the cylinder(s) overnight, (usually 1 and 2 for some reason).
And depending on how long it's been leaking, either a lot or little will sit on the top of
the cylinder(s). When the engine starts up, coolant doesn't compress so it gets
pushed to the top and covers the spark plug so it's can't spark, thus no thrust downward.
So no power, then what Parker said post #67.
If there is only a little coolant, it clears in a second or two and the engine starts. If there
is more coolant, it will take longer to clear it out, and then the new air/fuel being sucked in
can start to clean off the plug and then it sparks and off you go.
If it's really back, it can bend a rod, or two, and maybe explode the piston and throw it and
maybe the rod out the side of the engine....

That's why it's BEST to replace that head gasket at the first sign of leaking...

Also, condensation can form in the pistons when it's cold outside and a hot engine is cooling
down. This happens occasionaly and is not big deal as it's normal...