What exactly causes the HG to blow?

According to a recently-discussed European TSB where Toyota addresses the issue more directly than we've otherwise seen them do, they seem to have pinned it on the programming for the variable-speed water pump, allowing certain spots of the head/block interface to get extra hot in certain patterns of engine use.

 

it's the rings, no, it's the egr circuit, no wait, it's the 10,000 mile oil changes, no, it's the untested acidic coolant, no, it's the design of the head gasket, no...

 

Lol... Ya'll getting tricked and are replying to an early generation AI software post not based on a real person but a broken computer program that is long since outdated. They're using robots to test the respondents for how easily they're fooled.

Or rather to be clear, the use of the word "remember" is not used in a logical or rational way and maybe if this was a person in a foreign country perhaps they'd deserve the benefit of the doubt, but in Texas? I don't think so...

So enjoy your time talking to a fake AI robot that's seriously lacking in intelligence. As in even a village idiot knows the difference between the meaning of the phrase "I'd like to remember" and "I'd like to learn."

And don't get me wrong @Higgins909 was a legit participant back in the multiple posts in Late July and early August, but that's not the robot you're talking to right now in this thread.

 

Meh. Some other reader may come along any day and read the thread. So it doesn't hurt to have information there.

 

For head gasket preservation, my money's primarily on keeping the EGR components (including intake manifold) from clogging up with carbon. I'd recommend to do this at least every 50K miles. More info in my signature (on a phone turn it landscape to see signature.)

Just for giggles I also:

1. Do oil changes every 6 months or 8K kms (5K miles), whichever comes first. (This is Toyota Canada's stipulated oil-change interval for 3rd gen Prius, btw)
2. Have a quality oil catch can installed in the PCV circuit. Drain it at every oil change. Two actually, in series...
3. Have the Toyota Block Heater installed, and use it virtually without exception, for a couple of hours, before the first cold-start of the day.

 

So the european tsb states overheating causes the hg failure, of course along with the head gasket being upgraded later on, right? So in other words hg fails for one of the main reasons everyone already knows since 1925. Two main reasons, overheating and inadequate head gasket quality. So Toyota’s fix is to speed up the water pump under harsh conditions. I guess that assumes a non leaking system for that fix, so back to square one imo.

 

With that being said, you’d disagree with grill blocking Higgins 909 ?

 

if the main cause is hybrid heat cycling, why wasn't it as big an issue on gen 2?

 

Which Prius do you have in mind?

Leaving out the water pump for the inverter (that's a whole separate system), and the pump for the thermos in Gen 2, there were 2 water pumps serving the engine in Gen 1 and Gen 2. One was the usual mechanical one run by a belt, and one was electric, only to keep the warm water flowing when the engine was off but you wanted heat in the cabin.

Gen 3 got rid of the extra one just for the heater, and the one on the engine is electric, and variable speed, so they did what you wonder why they didn't. Not only can they turn it on when needed, they can turn it on at whatever speed is needed. And they can keep it on when the engine is off, if you want heat in the cabin.

The recently-mentioned European TSB puts responsibility on the code in the ECM that decides how fast the variable-speed water pump should run. So, none of that existed in Gen 2.

From the way they wrote the TSB, it doesn't sound like "overheating" is really the issue, in the sense of the overall coolant temperature ever looking too hot. Of course the thermostat opens wider, the ECM runs the pump faster, and at a point the fans even come on, the hotter the coolant gets.

The TSB seems to be more about the overall coolant temperature always looking ok, but where there is too little coolant flow sometimes (too low a pump speed) for the coolant to even out the temperature between the engine's hotter and cooler places. So the hotter places get too hot (and the temperature contrasts get too big), even though the coolant temperature measured in the one spot where the ECT sensor is never looks too hot.

 

Hot-spotting was eventually accepted as the cause for head gasket failures in the last Japanese-made aluminum engine I studied to any real depth.

It's a little comforting to find simple causes for these problems.

I do wonder if the electric water pump in the Toyota 1.8L could be gamed into running a little more, either with a spoofed ECT or a cloned/augmented PWM to the pump motor.

 

One theory for HG failure, that hadn't been brought up completely, is that the EGR gases (oily carbon gunk), slowly builds up in the intake manifold passages. Contributing to the problem, the buildup is uneven across the intake ports, with the heaviest buildup usually occuring at cylinder 1 > cylinder 2, and so on.

Since EGR gases are added to the intake charge to cool the combustion process to keep NOX emissions down, cylinder one will eventually run hotter and hotter. The HG typically fails at the thin section between cylinder 1 and 2.

Posted via the PriusChat mobile app.

 

Very few theories have been brought up more completely or more incessantly on PriusChat than that one, for some years now.

The European TSB from Toyota seems a relatively less-discussed addition to the conversation.

 

I think your inference is that makes it less credible?

 

Low tension rings dramatically increase blow by which returns via the egr and pcv, also a bad design due to its placement. Toyota acknowledged the ring problem and quietly replaced rings and pistons free for a couple of years. With no class action suit across many models with low tension rings, Toyota spent their rehab money on flawed inverters and brake boosters.

So why don’t low tension ring Corollas and Camrys slightly leak coolant past the metal head gaskets embedded black seal? Prius thermal cycling, demonstrated to reach deltas of 50f at times.

So why don’t gen4s have death rattles leading to expensive hg and engine replacements. Dramatic improvements to cooling around the cylinders and heads combined with a special insulator. Plus more head gasket sealing material embedded in the gasket. Once Toyota figured this out, hybrids show up in minivans, trucks and Corollas.

Gen4 Insulator


Gen3 PM? New pistons and rings combined with cleaned up head, valve seals and egr cooler. Older models benefit from the revised intake. A pro rebuilt engine usually possible for less than a dealer hg or used engine.

 

I would never suggest that anything becomes less credible simply because of frequency of repetition.

Or more credible, absent something else happening, like a visible progress where later repetitions supply additional evidence, address earlier gaps, and so on.

Nothing requires that credibility and frequency of repetition have anything to do with one another.

 

There’s always carbon coming out of the cylinders; doesn’t have to be an oil-burner.

 

In my opinion, a cylinder explosion occurs when an object that cannot be compressed, such as water or oil, enters a running cylinder, causing problems with the connecting rod, cylinder or cylinder head. The purpose of egr is to lower the combustion temperature, thereby reducing the emission of nitrogen oxides. If there is a problem, it may lead to high engine temperature. The materials of the cylinder and the cylinder head are different, and their thermal expansion coefficients are also different. When the temperature changes drastically, the contact surfaces (cylinder gasket) may move imperceptibly with each other, and tearing will damage the cylinder gasket structure and cause damage. Due to its design, the prius works with engine clearance, so the engine temperature changes more than that of ordinary vehicles, and the chance of cylinder head damage is greater. So reducing the temperature change rate and the cylinder gasket material may be the key. Under normal circumstances, do not step on the accelerator pedal vigorously for a period of time when the engine is just started, and frequently check the coolant, cooling pump and EGR system, which may reduce the chance of major failures.