Hybrid Vehicles and Head Gasket Failure

[The Critic]

This video was just posted by a mobile mechanic who specializes in head gasket repairs:

https://youtu.be/0lh49QHxSz0

In his opinion, the repeated warm-up/cool-down cycles seen on hybrid vehicles is largely responsible for the head gasket failures.

The 10-15 Prius seem to be especially prone to failures at high mileage and the same person also just posted a head gasket repair video for the Camry Hybrid with the 2.5.

What are your thoughts on the repeated warm up/cool-down cycles being the driver for head gasket failure in these applications?

 

[Lolvoguy]

What are they made with?
Is it a cast iron block and alum head?Or all alum?

If the latter of the two, I can't imagine the heating and cooling cycles being an issue...

 

[The Critic]

Originally Posted by Lolvoguy
What are they made with? Is it a cast iron block and alum head?
Or all alum?

If the latter of the two, I can't imagine the heating and cooling cycles being an issue...

Aluminum head and block.

 

[mk378]

"High miles." Also likely the coolant never checked or changed for the life of the car.

 

[The Critic]

Originally Posted by mk378
"High miles." Also likely the coolant never checked or changed for the life of the car.

150k+ is usually when the failures show up.

 

[ragtoplvr]

There is still some differential thermal expansion on all aluminum blocks, as the combustion heat is not evenly distributed.
They also use steel head bolts/studs, that will have less clamp pressure cold than hot.
Is there any thread failure in the blocks to go with this.
What kind of thermostat do they have, dump type of constant flow
Rod

 

[Lolvoguy]

Originally Posted by The Critic
Originally Posted by mk378
"High miles." Also likely the coolant never checked or changed for the life of the car.

150k+ is usually when the failures show up.

+1
Most seem to think "Toyota" and "hybrid" equates to limited/no maintenance required (aside from tires, brakes, and fuel).

 

[Kestas]

He never did get to the root cause for needing a new head gasket. Was it disintegration of the head gasket?... corrosion providing a leak path?... cyclic scuffing of the aluminum surfaces? How can he place blame on excessive thermal cycling and not provide evidence? It is just his opinion.

 

[PandaBear]

The same heating / cooling cycles have not impact the gen 2 prius. I think it is a bit more than that.

My take is, in gen 3 they become more aggressive in the compression / ignition timing and have less safety margin in terms of knock tolerance. This gradually wears out the head gasket.

Also, if it is repeated warm up and cool down cycles, the stats on the street would be skewed more toward cooler climate and family transport vs the commercial delivery duty.

 

[Job]

It's all nonsense five minutes of fame.

 

[domer10]

Originally Posted by Kestas
He never did get to the root cause for needing a new head gasket. Was it disintegration of the head gasket?... corrosion providing a leak path?... cyclic scuffing of the aluminum surfaces? How can he place blame on excessive thermal cycling and not provide evidence? It is just his opinion.


And this would be a far stretch? Excessive thermal cycling causes stress on a vast majority of certain materials, and especially if there are two separate materials attached to one and another under tension or pressure. Sometimes not everything requires a 3 year scientific study. Sometimes when people have experience in their field such as mechanics, and has more than likely seen this sort of issue in other applications.

I have a 3000 dollar pizza oven from Italy, that I can not use in temps below zero due to how hot it gets, and if it cools to quickly the stone will crack.

Sometimes common sense is evidence enough.

 

[slacktide_bitog]

Are non-Toyota hybrids having these issues?

The warm-up/cool-down cycle doesn't seem fast enough to be the cause of this issue. Otherwise, the hybrid head gasket problem would be more prevalent in Hondas, which shed heat so fast you don't even have to turn the heat on when bleeding coolant

When the engine shuts off and comes back on, the engine will still be hot (or cold) since the engine isn't off for that much time. Perhaps something like the Volt or the i3 REX maybe, but those aren't the ones with the head gasket failures.

Hot/cold cycles wouldn't cause it. Overheating would. If the engine is on and off, it would have a lesser, not greater, chance of overheating, unless they have some sort of lean burn mode (like early Honda hybrids from 20 years ago)

Do they have grille shutters? Maybe they don't retract when they should? Anything else that would cause them to overheat and damage the gasket?

Will this be the only time you have to replace the head gasket? Maybe it's just a poor gasket design (like most GM pushrod V6 LIM gaskets, where aftermarket revised gaskets keep the problem from coming back for good)? Or is it like Subaru that will eat head gaskets no matter what?

Originally Posted by Lolvoguy
Most seem to think "Toyota" and "hybrid" equates to limited/no maintenance required (aside from tires, brakes, and fuel).

To be fair, most Toyotas don't require much maintenance, even hybrids

Originally Posted by The Critic
150k+ is usually when the failures show up.


At least it's not 60k like Subaru

Wait, did Subaru have any hand in designing these? Subaru doesn't even make hybrids!

 

[PandaBear]

Originally Posted by slacktide_bitog
Are non-Toyota hybrids having these issues?


Even older gen 2 Pri don't have this issue.

 

[eljefino]

My 2nd gen prii do have a lean burn mode, but it's only at idle AFAIK above 41 mph. Below that speed the engine quits entirely if the system is happy with everything.

There's a reason these things don't have dash temp gauges. Watching the scan tool data, it's all over the place until ~30 minutes have gone by. The first few burps of the thermostat let a lot of cold water in, and the first few ICE shutoffs in traffic have the same effect.

 

[JHZR2]

Originally Posted by Lolvoguy
Originally Posted by The Critic
Originally Posted by mk378
"High miles." Also likely the coolant never checked or changed for the life of the car.

150k+ is usually when the failures show up.

+1
Most seem to think "Toyota" and "hybrid" equates to limited/no maintenance required (aside from tires, brakes, and fuel).


Lots of vehicles need HGs at 150k. For all the chest thumpers who buy a car and claim that their requirement was to take it to 200 or 300k or more, it's just not typical, and rarely achieved.

Lack some maintenance, or have a manufacturing outcome within limits but that is a bit thinner, or perhaps allows a stray current to pass, and... failure at some point. Lots of things fail, nothing is infallible. 150k of routine grocery getting use is a lot of mileage. Much different than highway cruising.

The micro cycle theory is a good one. Ive been concerned from the start about how I can be accelerating uphill on the interstate at 80mph, crest the hill, and the engine turns off. Perhaps oil and coolant is still flowing, but it has to be a lot of heat and heat soak at critical points in there. Since hybrids aren't as great on the highway, and IMO it is more stressful, I wish there was a way to force the engine to stay on for longer term highway cruise.

 

[CR94]

Originally Posted by PandaBear
Originally Posted by slacktide_bitog
Are non-Toyota hybrids having these issues?
Even older gen 2 Pri don't have this issue.
In that case, the next question should be "Are post-2009 Corollas having this issue?" They have a non-hybrid version of the same engine; I don't know whether the head gasket is identical.

 

[4WD]

Originally Posted by PandaBear
Originally Posted by slacktide_bitog
Are non-Toyota hybrids having these issues?


Even older gen 2 Pri don't have this issue.


We have a 2014 Fusion Hybrid with 121k and no issues …
guess the head gasket will go at 149, 999 miles

 

[clinebarger]

Originally Posted by CR94
Originally Posted by PandaBear
Originally Posted by slacktide_bitog
Are non-Toyota hybrids having these issues?
Even older gen 2 Pri don't have this issue.
In that case, the next question should be "Are post-2009 Corollas having this issue?" They have a non-hybrid version of the same engine; I don't know whether the head gasket is identical.


The 2ZR-FE used in the Corolla is not exactly the same as the Atkinson Cycle 2ZR-FXE used in the Prius. I don't know the exact effects of the Atkinson Cycle combined with High static compression on peak cylinder pressures.

Thermal Expansion causing Gasket "Scrub" is a very real phenomenon.

 

[Kestas]

Originally Posted by domer10
Originally Posted by Kestas
He never did get to the root cause for needing a new head gasket. Was it disintegration of the head gasket?... corrosion providing a leak path?... cyclic scuffing of the aluminum surfaces? How can he place blame on excessive thermal cycling and not provide evidence? It is just his opinion.

And this would be a far stretch? Excessive thermal cycling causes stress on a vast majority of certain materials, and especially if there are two separate materials attached to one and another under tension or pressure. Sometimes not everything requires a 3 year scientific study. Sometimes when people have experience in their field such as mechanics, and has more than likely seen this sort of issue in other applications.

I have a 3000 dollar pizza oven from Italy, that I can not use in temps below zero due to how hot it gets, and if it cools to quickly the stone will crack.

Sometimes common sense is evidence enough.

In my business you don't guess at the cause of a problem. You find the root cause of the problem before initiating a fix. What if the engine had a cracked cylinder block or a crack behind the valve seat insert? A new head gasket won't solve that problem.

I've had clients try to save money by using "common sense" to fix a problem instead of having me find the root cause. They waste a lot of engineering time and money putting the wrong solution in place before they ask for my help.

 

[supton]

Originally Posted by JHZR2
Lots of vehicles need HGs at 150k. For all the chest thumpers who buy a car and claim that their requirement was to take it to 200 or 300k or more, it's just not typical, and rarely achieved.

Can you quantity "lots"? There was a rash of Subaru HG's, as noted here, and now there is a rash of Prius HG's. I'm not sure I've heard much squabble here for anything else?

I'm not sure what to make of your statement that it's not typical to run past 200k. I can accept that I'm a non-typical driver (keeping vehicles for 10+ years and >200k). Would that mean it's ok for me to buck the trend here and to avoid certain tech and certain models since I'm not typical? or that any purchase would have to be made with the expectation of certain repairs being a near certainty?