Loud rattle when engine kicked on

“ too little too late” for the EGR cleaning

Although the EGR cleaning needs to be done when you do the head gasket. If you were having a shop do it it should save you a little money doing the EGR cleaning at the same time because there is some combined labor.

 

It’s probably the dampener that you are hearing. It is mounted between the engine and transmission. It is the part that joins the two together kind of like a flex plate on a traditional car. I would have your mechanic change the plugs and check the piston for carbon using a borescope. If you have clean pistons it’s getting coolant in the combustion chamber.
I would try to avoid the dealer! Very high cost

 

The noise does come from the transaxle, the clutch damper assembly to be specific. When a head fouls a plug with coolant you have a severe misfire for a few seconds. That causes a loss of synchronization between the engine and the transaxle. The electric motors have to maintain a synchronous rpm on the planetary gears connected to the engine through the clutch damper. When a mismatch occurs the clutch damper slips causing the severe mechanical noise. Most conventional mechanics and some on Priuschat have never seen the issue and have a hard time correlating it to a head gasket leak.

A bad plug or coil can cause the same thing but rarely go bad. Those failures don't clear up.



Weber State University video showing clutch damper from a gen2 (about two minutes from 5:40)

 

Yes. I have seen it many times. Some shops are doing three a week. There is nothing wrong with the clutch damper, it is just the noise you hear.

 

The engine shaking is caused by a fouled plug due to the coolant getting in the combustion chamber. If you continue driving it that way further damage will happen I have also seen the dampeners get damaged from the constant slamming back-and-forth (the rattle you hear)

 

It’s hard to say I do all my own work so I would keep the vehicle. If you are paying somebody to fix The repair cost at some point will not make since. I also don’t know your financial situation.
Here are some of that other things that fail often on the third-generation Prius. And prices to repair it depending on your location prices may change.
Brake actuator/booster. 3000
Hybrid battery. 2000-3000
Head gasket 1500 and as high as 5000.

With all that being said the car market is crazy right now. Depending on the condition of your vehicle you might get quite a bit on trade-in however, you would have to buy a vehicle that is over priced.

 

Most of the 2017 and newer CRVs have a 1.5L turbo and a cvt transmission. We get about 34 mpg lifetime. The 2.4L engine in the older crvs and the base model 2017 and 18 models is conventional and gets around 25 mpg. AWD get reduced mpg.

A Prius headgasket job at the dealer will cost as much as a rebuilt engine elsewhere. Rebuilt is far better since the original engine came with flawed piston rings.

 

It Could not have been said it better rjparker.

It would be great if someone could chime in your area and let you know of a good mom and pop shop that will work on a Prius. Dealer is to much. Also their diagnostic skills are not always the strongest.

 

Side note I had a 2007 CRV with the 2.4 engine and a manual transmission. We got about 20 miles per gallon. Although we lived at 5000 foot elevation and we where constantly driving up and down the hill.

 

The damper noise is an outcome of the problem, not the problem itself. Well until it's springs fail. It ties back to head gasket failure:

If the head gasket is failing, coolant leaks into the cylinders (typically starting with cylinder one), piston coming up encounters (uncompressible) coolant, balks, and that reverberates down the piston arm, to crankshaft, and on to the damper.

And the head gasket failure is also an "outcome", of clogged EGR system, my 2 cents.

 

That's kinda conventional wisdom by now, but some pieces of the puzzle are still missing, in my opinion. That doesn't explain frequent reports of alarming misfires several years ago of engines too new to have a head gasket issue, clogged EGR components, or bad spark plugs. It doesn't explain why misfires were often reported the first time an engine was started after having been run only very briefly the previous time it was started. It doesn't explain why my car has demonstrated the noisy misfire issue, but only 3 or 4 widely separated times in nearly 8 years and 90k miles I've owned it. The last time it occurred was a few months after I cleaned out the manifold EGR passages. No other symptoms.

 

With EGR, I'm inclined to "shoot first and ask questions later". Pretty much every head gasket failure on a 3rd gen also has EGR clogging. And then there's @ASRDogman , well north of 300K miles, on top of the cleaning, and on the original head gasket AFAIK.

There could be other misfire causes, but any 3rd gen of a certain age (>100K miles) should get the EGR cleaned stem-to-stern. There's no puzzle for me on that.

What I was trying to get across in what you quoted, is that the damper is just the messenger; it's balking because something upriver in the causal stream is not right.

 

1) Unless the car is rusted through, it is worth fixing for the utility value of a dependable car getting fantastic gas mileage in an age of $5/gal gas. You may well "invest" more than you could resell the car for, but you are very, very unlikely to be able to buy a better car for that same amount of money.

2) You absolutely positively should not have a Toyota dealership fix it. Toyota mechanics rarely fix things, they usually just swap out bad parts for good under warranty. Outside of warranty they charge premium labor rates to customers without providing premium service. If it has a bad head gasket, they'll probably want to install a new engine. They may offer to install a used engine, but they probably won't even replace the gaskets on it.

I would instead search google maps for "hybrid repair" or "prius repair" and see what shops pop up. It looks like there are a number near Cincinnati (less so toward Cleveland). In truth, any independent auto shop can do a head gasket, but it'll be a normal job for a prius/hybrid specialist so you're less likely to have them run into slow-down issues.

The start-up rattle occurs when there is excessive moisture in the intake and/or cylinder. When these cars were new, that was often the result of sticky EGR and/or moving the car across a parking lot when cold and having condensation build in the intake manifold. It probably is still the cause of your very sporadic issues.

When a start-up knock occurs regularly, the cause of the excess moisture in the cylinder is almost always a bad head gasket. Often these head gasket leaks start off small and somewhat seal themselves when the engine is warm, which means the start-up rattle happens only when cold. Eventually the gasket gets bad enough that the start-up rattle occurs even on a warm restart (like after being stopped at an intersection for a red light).

The fact that they have not already done a block test tells you this dealer/mechanic is not competent enough to demand dealership labor rates. It takes 3 minutes max to verify a blown head gasket and blown head gaskets are so common with gen 3 Prii that is should be the very first thing they check with a habitual start-up rattle.

Autozone even has loaner block testers: https://www.autozone.com/loan-a-tools/loaner-blown-head-gasket-tester