My engine bangs and shakes violently

This goes on a good bit with this model replacing engine is actually quite normal or you're buying the pieces to make a new engine as it is If it's not shaking itself apart yet you can replace this reciprocating mass the short block whatever you want to call it the middle of the motor use your pieces that are all around it the girdle the oil pan etc If you must that might be something to look into because everything else is well not a complete functional ready to go solution.

 

That symptom is associated with a blown head gasket. If it has been that way for long, there may already be damage to one or more rods, and that means a replacement engine is the best fix.

A blown head gasket is best diagnosed by a borescope in the spark plug hole while pressurizing the cooling system with a test kit.

 

how many miles on her?

 

Are there any codes?

 

Second this. Also:

At what miles was the EGR "roughly" cleaned? How "roughly"?

How long have you had the car, and if second hand, at what miles did you acquire it?

How's the oil consumption? (a factor in deciding what course to take)

 

Leak test first. If it fails, new engine. If pass, check plugs. If plugs are fine, be initiated to the egr cleaning club.

 

Codes?

 

a 'roughly' cleaned egr might not get the tiny intake manifold ports?

 

yep, great cars till the engine goes. then the brake actuator. then the battery. then you're good for another 180k

 

A new ignition coil fixed the shaking death rattle on my 2012.

 

The latest I would leave EGR cleaning, a thorough cleaning, is 100k. 50k is safer.

I would start assessing the head gasket; sounds like your mechanic has already.

 

Your mechanic is right.

But you could do a borescope inspection when cold but with manually pumped up coolant pressure. Use a quality dual view tool. Steam cleaned piston really is enough.

HG Borescope at 10:57

One thing that is indisputable about gen3 hg fails is the black sealing layer of the metal head gasket erodes away allowing a seep of coolant into the cylinder. For the first few months or even a year it only happens after an overnight cooldown of the engine. Sometimes it causes a misfire severe rattle and shake; often it does not. The hg seals quickly once the engine is running. At first there are no codes but the shake is unmistakable. The parts cannon is fired. No detectable hydrocarbons in the coolant. No change of compression. No coolant in the oil. No observable coolant reservoir drop. New spark plugs often clear the symptoms for a week or two.

Traditional blown hg causes still apply such as overheat with warping and loose head bolts. But other triggers exist. Some think old coolant eats away at the head gasket sealing layer. Carbon buildup does generate preignition which is quickly detected by the knock sensor but still occurs. Some gen3s get so carboned up the preignition is audible especially when combined with a low hv battery. Aluminum engines warp.

Toyota significantly changed the cylinder cooling passages, head gasket sealing area and cylinder wall heat distribution in gen4s.


Prius Head Gasket Early Options

History repeats itself with gen3 engines. You have several choices:

1. Spend $800 for a dealer intake and egr cleanup or dig into it yourself. Not a simple job. Will not fix your early stage head gasket leak.

2. Change plugs, coils and maybe injectors when it starts throwing misfire codes. It does not seem to lose coolant and passes a coolant hydrocarbon test. The parts cannon is the common neighborhood mechanic reaction at this point. Not cheap, another $1,000 thrown at it. You get a month or longer reprieve before you realize this was a waste.

3. Continue waiting until the shudders are every week or so. Soon it will rattle at stop signs. Shortly after it is obvious - the coolant is low. It has been months and maybe $1800 after the first warning. The writing is on the wall. Now the repair is a replacement engine. Some will just do the head gasket. In many cases it will fail in the near future because too much time has past. The dealer will recommend a rebuilt engine to eliminate bad rings and they will clean everything like new but the cost scares you. At this point, a rebuilt engine is the right answer for three or more years of ownership.

Or you find a quality shop now and have the engine torn down. The cylinder head is carefully inspected, cleaned and rebuilt by a machine shop. The quality repair shop installs a new gasket set. While they are doing it the egr cooler and intake manifold are thoroughly cleaned. The shop should have enough confidence to give you a year warranty. You don't get new rings so a trade within the next couple of years should be scheduled.

Or you trade now and punt the issue. Don't sell privately, let a dealer auction get it.