What causes headgaskets to blow?

Doesn't really matter it happens when you see one of these heads off and what goes on and where the leak starts and the seepage starts to go on and all that It seems like there's a spike in temperature maybe like internal combustion temperature goes up because the EGR flow has gone way down. In most engine designs EGR is used to keep the internal combustion temperature under control when EGR is no longer there or in the amount expected it can create hotspots then your gasket is not very forgiving for any of this like the old fell pro blue PT permanent torque gaskets were designed The newer all metal five or three or whatever many plates of metal that are in use now in these newer gaskets require extremely flat surfaces no mistakes and no heating issues The minute that rises it's ugly head bam head gasket failure and directly after that connecting rod failure and then you're needing an engine. These open deck design engines have no meat on any of the metal parts to do any machine work so everything gets replaced It's not like the old days where you could just shave all 50,000 off the head and carry on and do the things in the machine shop to rebuild the head deck the block all this sort of thing It's just no metal left in the castings for these operations removing all that metal removes a few pounds which in turn helps with gas mileage but doesn't help with longevity and strength so it's a trade-off Toyota took the trade off that may have you searching another car faster might be something I would do too if I was making expensive things like cars washers and dryers etc Just look at the products that you buy today like your washer and dryer $3,000 for a Samsung wash tower that longevity will be maybe 7 years My washers and dryers have lasted 25 and 30 most of my life no kidding so there's always things like that Toyota's it used to go 3 to 500 mi easily with poor oil changes and minimal work and all of that poor person stuff just doesn't really happen anymore today they've engineered that out it seems like they need to sell more cars hello.

 

There are a few theories going around.

The one I support is that the engine gets inconsistent / insufficient coolant flow from the computer-controlled variable-speed electric water pump. This results in uneven heat distribution across the head-and-block assembly, and after enough cycles the gasket fails.

Uneven heat distribution is kind of the OG problem with aluminum engines. It's a common killer of head gaskets.

I've never felt that a proactive replacement was of any value. It's the sort of problem that gives you a fair warning sign or two, so you might as well take advantage of them. Not every car will pop its gasket, so it is worth playing the odds. The important bit is to be ready to go when you do see the signs. Don't delay.

 

My take, the head gasket failures are primarily due to carbon clogging of the EGR components, including the EGR passages in the intake manifold.

Should ideally cleaned every 50k miles. Do engine coolant changes at same interval is practical. Or delay first cleaning to 100k, at the latest.

It’s not the head gasket being defective; the clogged EGR is the culprit. Remember in Dumb and Dumber, “our pet’s heads are falling off”?

I’d replace water pump before 150k too.

 

How many miles on your vehicle?

There is not a REAL answer about the head gasket failure. Many factors are involved.
Mine just started at 301,000 miles, it was minor. I changed it shortly after that.
I had planned on doing it the following weekend, before it started to go... So I caught it
early.

It's hard to say if changing it early is good or bad. If you have low mileage, it's not worth it.
Unless the engine was overheated.

From what I've read, those who drive mostly in the city seem to have the most early failures.
Highway drivers seem to go longer.

If you read the maintainence manual it will tell you when to do what. Plus there are many sites
that will tell you. It's pretty simple and easy to do.

The head bolts are stretch bolts, there really isn't any retorqueing to do.

Some think changing the water pump prevents failure. I checked mine at 267,000 miles,
and it was fine, no cracks(the impeller). But, I dropped it as I was reinstalling the water pump, and
the impeller broke. So I had to put the new impeller in.
I will turn 340,000 miles this week.

Next week I will be replacing the hybrid battery. The OEM one is failing. Twice I've gotten the
P0080 or watever it is, in the morning when it was at 2 bars. I was able to clear it with the D8 and
drove for 2 weeks. I was searching for the best price on a battery because I knew it was just a matter
of time, when it happened again on Wednesday. Again, able to clear the codes and drive on.

The Prolong system kept it going for the last 4 years or so, so I'm happy about that!

 

It's truly amazing how many miles you got out of it before having head gasket and water pump problems. At what mileage did you start cleaning the EGR system and start having oil burning problems? Do you have a catch can? I've got 115K miles on my 2013, and have done the coolant change at 100K miles and have been recently doing oil changes from 10K to 5K miles. I don't have oil burning problems. I'm probably going to trade in or sell the car within the next year. I plan doing a spark plug change at 120K miles or the next oil change like the manual says. I'm thinking that engine problems (including the head gasket) are related to people not doing the prescribed maintenence in terms of oil and filter changes with the prescribed engine oil and coolant changes/ proper coolant, and have a bearing on how the car is driven (heavy acceleration and lots of stop and go driving is detrimental). I'm an unbeliever in the EGR system having any relation to head gasket life.

 

At 115,000 you won't have to worry about the head gasket. You'll see coolant going
down. I never saw the coolant go down until I knew the gasket was starting to go.
Then it only went down the thickness of the seem in the coolant tank.
I was the 2nd owner at 116,??? miles. He had about a 2 inch thick stake of paper work
of all the maintainence he had done from Toyota.
I started out at 10,000 mile oil changed then went to 7500 and now do 5000 miles.
The engine was burning 1.5-2 qts per 10,000 miles, then slowly start using more. Thus the
reason for the 5000 miles changes.
I currently use about the same for 5000 miles. I drive 65mph or less 95% of the time.

I've been using seafoam the last 3 oil changes, and the new Valvoline Restore and Renew oil.
It's "supposed" to clear out all the deposits 100% in 3 oil changes. I'll be doing the 3rd oil change
Monday. I am not sure if either the seafoam or oil is doing anything to clean out the deposits for
the oil rings on the pistons. But since it was only about $4-5 more for that oil, and $5 for the seafoam,
I figured it would hurt to try it out. Though, the oil is certainly a lot nastier when I've changed it!

I know I'm going to have to replace at least the short block sooner or later. Or get a remanufactured
engine from the Hybrid Pit because it would be easier to pull the whole engine and transfer the compressor,
inhectores, etc then doing all the work to replace just the short block.

UPDATE: The water pump did NOT fail. I dropped the pump as I was reinstalling it, which in
turn broke the impeller. The magnet area was still intack, and not swelling. It turned easily, just
like the new one....

 

A failing head gasket in a 3rd generation Prius can announce itself as mysterious coolant loss, a rattly hard knock at startup that clears quickly, and a sweet coolant smell around the car and tailpipe. Things eventually get worse, but those are some early things to look out for.

If you catch it quick, you're only paying for a gasket job.

If the hybrid battery totally fails, the hybrid ECU will not be able to start the gas engine and the car cannot be driven. It won't go to READY mode.

 

All you have to do is look at what changed on gen4 when the excessive hg problem went away.

Redesigned cylinder and head cooling passages. A foam insulator next to the cylinder walls to prevent uneven temp from the top to the bottom of the cylinder. Better pistons and rings different than the gen3 retrofits most don’t have unless there gen3 is late 2014 or 2015..

Gen4 Cylinder Insulators


And yes, an improved egr system that takes cleaned exhaust after the cat rather than before in gen3. Gen4 has a larger egr cooler seeing hotter engine coolant before the heater vs after in gen3. Gen4’s egr valve also added coolant flow.

There are enough gen3 engine design flaws to make user maintenance efforts ineffective. Especially gen3 egrs which don’t clog up or code if the engine is not burning excessive oil. Which is a design flaw Toyota acknowledged with a TSB and fixed free for early oil burners.

What to do? Change oil from day one every 5k miles. Seems to work but few have that opportunity today. Toyota changed oil changes from 5k to 10k miles with gen3. Plus they started giving free oil changes for the first 25k miles which got buyers used to it.

All of which is why a gen3 rebuilt engine with new pistons and rings is better than a simpler hg repair. And is the reason why some resort to using a gen4 block in their gen3 vehicle, even though they still use the gen3 egr and intake.

 

There are things we cannot see: changes to the control system for the variable-speed coolant pump.

We know Toyota issued updated firmware for vehicles delivered in Europe, but the same update was never applied to US vehicles.

It is likely that the 4th generation Prius has an updated control system for that pump, calibrated to work in harmony with the other improvements you've noted.

 

There have been reports of the 4th generation head gasket failures..... So it's not completely fixed.

 

There was a YouTube video posted by Gasket Masters that said they are seeing a lot of high mileage Gen 4 engines needing new head gaskets, so it seems that the problem may be mitigated somewhat, but has not been solved. It also seems from what I've read here that some have tried (unsuccessfully) to put a Gen 4 engine in a Gen 3. Overheating problems seem to be a problem with this swap and (of course) overheating kills head gaskets.

 

some gen 4 head gaskets likely caused by low coolant due to the ehe leak

 

Yea, there was something about the heat exchanger in the exhaust under the car.
It cracked or something and coolant leaked out....

 

Driving if the car is overheating will kill a head gasket, but this is rare in Toyota's...you'd have to ignore a few warning lights to do this.
Also, not doing proper maintenance like getting old coolant replaced and not doing regular oil changes will also lead to head gasket problems....even in Toyota's.
Oil changes every 5,000 miles or 6-months and coolants (both invertor and radiator) get serviced every 5-years or 50,000 miles, whichever comes first.

 

@ASRDogman , me too: when did you do the first EGR cleaning, at what miles?

 

Any car will blow a head gasket if it overheats and there is no easier way to overheat than to leak coolant out the exhaust from a cracked gen4 exhaust heat exchanger. One problem with a lot of today’s drivers is they don’t know what the warning lights mean and when or if they should stop immediately.

 

That doesn't seem be happening with third gen though. Not once reported here IIRC.