Underlying Cause of Head Gasket Failures?

impossible, the priuschat moral police would have stopped & jailed the perps even before gasket sealant is poured in! Your giving permission for people exercise such practice.

 

Cleaned the intake manifold, EGR circuit, installed oil catch can(s), just past 70K kms. Will likely revisit the EGR with the spark plug change, at 12 years, and likely around 100K kms.

Not burning ANY oil so far, doing 6 months oil changes, at undisclosed kms (don't want to be hauled off...). At oil changes I put in 4.2 liters, and it's about 1/8" below top mark on dipstick. When the next oil change rolls around, hasn't budged.

 

That is the expansion ratio. No normal Prius has anywhere near that much compression.

 

What is happening on the power stroke is that the charge is expanding. As fuzzy1 correctly pointed out, the ratio by which it expands is known as the expansion ratio.

The charge is only being compressed on the compression stroke, and the valve timing makes that ratio less than 13:1. That's what makes the engine an Atkinson-cycle engine: the fact that its expansion ratio exceeds its compression ratio.

The engine does indeed have a knock sensor, like pretty much any other modern engine, and does have to be able to react (such as with ignition timing) to keep itself out of knocking conditions, like pretty much any other modern engine. None of that is because of "13 to 1 compression", which it doesn't have.

 

If you replace the head gasket without addressing the root cause of the head gasket failure, it's "probably" going to fail again, don't you think?

It's easy to blame the OEM for building a car that won't last much more than 120,000 miles with a 10,000mile OCI, and modern drivers that pretty much expect to maintain a closed-hood maintenance philosophy.

There ARE some design issues with the G3, as there are with any car.
IMHO the EGR circuit is prone to getting plugged up, the oil sump is about a quart too small, and the OCI is too long.
The pistons are well documented as well.

You CAN inform yourself of some of the design issues with the G3 and mitigate some of the those by doing some of the things we talk about in this forum...like oil catch cans, reduced OCI, and oil level checks at least as often as required by the OEM.

Most people don't.
They sell the car at some point and owner #2 gets an unhealthy middle aged car with almost a 100 percent blockage of the left anterior descending (LAD) artery.....commonly referred to as....a widowmaker.

Next thing you know....the G3 Prius get the same reputation for quality and longevity as Fiat.

Remember that the cars are built in Japan, and they generally do not amass the same number of miles that their US spec card do, AND YET the Japanese also have used Priuses quite successfully as fleet vehicles (taxis) as have companies in the US.
Just a guess here, but fleet operators (even MINE!) have different maintenance modalities than private (gas and go) drivers.

THIS is why.....ACTUAL mileage WILL vary.

 

do we have a conclusion yet? i've got almost 25,000 miles on my engine, and i'm getting nervous...

 

i’m nervous about the hv bat not getting charger cycles if you got 25,000 miles only on the car

 

He has a pip.

 

i am a pip

if only toyota would disclose the truth, i'm sure they know the facts

 

Concur.

 

The dots I connect:

1. Cylinder 1 is where predominance of 3rd gen gasket failures start.

2. The intake manifold’s EGR capillary passage for cylinder 1 always seems to clog first.

 

Um, interesting question and discussion.
I venture to say in many cars head gasket failure is attributed to water jacket location or high compression (or an over heat condition).
Coolant flushes can be a good maintenance item to reduce risk.

I don't recall anyone every mentioning re-torqueing the head bolts.
A common initial critical fastener check on motorcycles as a general example.

Predicting failure can be futile.
So, I could suggest a head bolt re-torque at an initial 10K service and a follow up at 50K.
But, I have not done this nor am I too concerned.
FWIW

Have fun.

 

Since you have a GEN 4 Prius and not a GEN 3, that is a consensus view.

JeffD

 

Well, the service procedure for cylinder head installation shows a "torque + angle + angle" sequence on the head bolts. So they are torque to yield (or torque to angle).

What would you have the head bolts "re-torqued" to?

Posted via the PriusChat mobile app.

 

His 2016 Prius v would have a gen 3 engine, identical to 2015 Prius I think. That said, I wouldn't touch head bolts.

 

I had understood that only the 2016 Liftback was a Gen4. The 2016 'v' and 'c' were still Gen3s.

 

FWIW, The Critic noticed that one head bolt seemed looser than the others on HG removal. With no warping of the head, it seems unlikely the bolt was stretched by local heat. But it's a fun data point.