Clean everything still knock when pressing on gas pedal

No, it isn't "too old," but it's defective. Is coolant level dropping fast yet?

 

head gasket?

 

When did you do all this? Recently? Should have been done at least 150K back.

Leak down test to confirm, but very likely head gasket has failed. How's the engine coolant level in reservoir?

 

You probably did, but make sure you got the little EGR ports on the intake manifold clean. I don't think it's in the popular EGR cleaning (edit: I mean intake manifold cleaning) video so it's possible people are missing it.

 

These:



A long/skinny bristle brush with a shot of brake cleaner is good. If it's really clogged you may need to start with some sort of pick.

 

idk if this is any help or not:

watch

head-gasket-replacement

 

If it rattles only after parking for few hours, probably head gasket leaks. If it rattle only on hard acceleration, it is not head gasket. Something else from the exhaust, timing chain tensioner. Worn vvti gear rattles only split of second and the timing chain guide could be more than 1 second rattle.

 

I have a similar problem with my 2014 Prius (225k miles). I had the EGR system cleans in Jan of this year, the transmission flushed and refilled as well at a hybrid shop. Recently, I am getting hard shakes from the engine when cold starting and sometimes when I stop and then accelerate to make the engine kick on. It will also do it while idling when the engine turns on to charge the battery.

Also, had a cylinder misfire code popup and then clear itself out.

Changed out the spark plugs but that didn’t fix the issue. Took it to my mechanic and he told me the engine isn’t rattling, it is coming from the transmission… he said my coolant levels don’t appear to be decreasing. I generally drive 100-200 miles a day and it drives fine otherwise. No issues when going higher speeds… is it the headgasket? What could be wrong with the transmission if that is what is rattling?

 

Remove the spark plugs, shine a light into the cylinders. Do any look wet?
If you rent a pressure tester you can put pressure on the coolant system and probably
see coolant easing onto the piston.
How does he know you aren't loosing coolant? Have you filled it? I won't take a lot to
get the knock.
You need to find someone who has experience working on a Prius.

 

The rattling is the "planetary gearset" I believe. It is part of the transmission, but it's just a generic noise that you get when you have engine misfires on these cars. The "death rattle."

It sounds like you have a blown head gasket, but the lack of coolant loss does give you hope. It could be anything that causes a misfire. Is it every cold start?

Was the intake manifold ever cleaned?

 

Generally gen3s allow coolant into the cylinder, particularly after a complete cool off. The coolant may or may not temporarily foul the plug. At first the engine heats up and stops the coolant loss before it is really noticeable except for startup rattling. The plug starts firing and the engine runs fine, typically for the rest of the day. People incorrectly think it is plugs, coils, injectors or clogged egr, even though it runs fine after a few seconds, wasting time and money.

Occasionally the startup rattling and short duration coolant fouling may bend the connecting rod slightly. This is often unnoticed during a head gasket job, leading to a second failure a few miles later when the rod goes. Or the rattling is masked with a sealer allowing more time for the bent rod to break.

The engine to transaxle damper is just that, a short term slippage mechanism when the engine rpms are not exactly matched by the electric motors through the planetary gears. This slippage is the startup rattling you hear. There is no mechanical disconnect like you get with a clutch or torque converter.

 

Way too late.

 

better late than never.

 

apparently not every cold start. No issue on startup this morning…

 

Getting the headgasket checked at a hybrid shop today. What are the best options if it is the headgasket on a 2014 225k car? Gen 4 engine? Fix headgasket?

 

They did a combustion test on the coolant and it changed color indicating O2 in the coolant and a definite leak in the headgasket.