Oil Catch Can

Some mechanics have argued that this is why you shouldn't use a catch can as all that fluid is best burned off in the engine. But most of us disagree... And 2010-2015 Prius have a greater need for a catch can than newer Prius because the EGR was poorly designed in that version and runs dirty.

 

How many miles did it take it to fill, and roughly what was the volume? Sounds odd, if it's filling up super fast.

With our 3rd gen it's maybe 50 cc every 2000 kms.

 

Yeah, @Mendel Leisk has some good links in his EGR cleaning section in his signature above. Hopefully he finally got around to updating the broken links?

 

That’s about a grands worth of parts, for starters. There’s no way they would just do that. And, replacement engine with the still-clogged EGR and intake manifold is a recipe for another blown head gasket, in short order.

my 2 cents: clogged EGR causes head gasket failure, and head gasket failure causes the cold-start knock, broken damper (twixt engine and transaxle) bent piston arm and so on. Periodically cleaning the EGR will prevent these problems.

 

It might be more accurate to say a functional EGR reduces combustion temperature and head gasket failures tend to happen when combustion temperatures get too high or are inconsistent throughout the chambers.

Not that I disagree with saying head gasket failure is caused by a clogged EGR, but there's some on here, as well as within Toyota who argue it's not direct cause and effect, which is likely why Toyota doesn't require EGR cleanings in their regular maintenance plan.

As in you'll start less disputes and be more accurate with the way I worded it above.

 

In my signature? I can take a look.

 

and even that is still too much handwaving to really be useful to anybody.

Part of the trouble lies in glossing over how many different 'temperatures' have to be talked about.

The intake stroke pulled in something like a quarter of a gram of air mixed with some fuel. That quarter gram of stuff got ignited, and its temperature followed a curve up and back down, and then it got shoved out the exhaust port, taking most of its heat with it. When EGR is used (which is not under all engine use and load conditions!), it makes that curve more wide and squat. The peak temperature reached by the quarter gram of stuff for an instant at the top of that curve is the temperature that EGR reduces. That's important for emissions, because at the higher peak temperature, nitrogen oxides form, which we use EGR to prevent.

But that peak temperature hasn't got so much to do with the temperature of the head gasket, or of the large masses of aluminum that the gasket is sandwiched between. Those stay at temperatures much lower than the quarter gram of burning stuff itself hits. Aluminum has a high thermal mass comparable to that of concrete, and it does pick up some of the heat given off by the quarter gram of burning stuff, over the whole time that it burns. The amount of heat picked up depends more on the whole area under the curve of the burning stuff's temperature, not so much on whether that area is wide and squat or tall and skinny.

What heat does get picked up by the massive aluminum block and head gets carried away by a pumped flow of coolant, whose temperature is regulated by a thermostat and radiator. The capacity of that cooling system is already big enough to cope with the difference in heating when you drive up versus down a hill, or accelerate versus coast, far bigger differences than between wide/squat and tall/skinny temperature profiles of the burning stuff.

I think that's probably why I have always struck out when trying to find anything in published literature about EGR and head gaskets that treats the temperature as being a big deal.

On the other hand, there is definitely published literature that treats the timing as a big deal. How, after all, does EGR turn that tall, skinny temperature curve of the burning stuff into a wide, squat one? By making that quarter gram of stuff take longer to burn. The flame front has to propagate to new hydrocarbon and oxygen molecules that haven't reacted yet, and the EGR spaces those further apart with non-burning exhaust gas molecules between them, so it takes longer for the whole charge to burn.

Because the peak of cylinder pressure is still wanted about 14° after top dead center, the spark then has to be advanced further before TDC to give the slower-burning mixture time to reach peak pressure. But what if the ECM thinks EGR is happening, and advances the spark that far, but really EGR isn't happening? Then the mixture burns much faster and the peak pressure comes too early. If the pressure gets too high too early, there may be pockets of the not-yet-burned mixture that ignite on their own before the flame front even reaches them—detonation—with a very sharp resulting spike in pressure.

And unlike how hard it is to find published literature on EGR that makes a big deal of the combustion temperature in relation to engine damage, there is definitely attention paid to the risk of damage through detonation.

That's the reason the ECM is careful to retard the ignition timing if it ever has detected a problem with the EGR. But one problem that it hasn't got sensors to detect is different degrees of clogging among the four EGR passages in the intake manifold. If some are clogged more than others, opening the EGR valve a little further can make the EGR flow look right overall. But that can mean some of the cylinders are getting too much EGR, and might misfire, while others are getting too little, increasing risk of detonation because the ECM is unaware of a problem, and it isn't protectively dialing back the spark timing.

 

I’ll just stick to broad strokes, don’t want to micro analyze the issue. My interest is selfish: I’d like preserve my engine, and won’t lose any sleep if I’m overdoing the EGR cleaning a bit.

So far I’ve heard of ONE guy claiming to have cleaned the EGR regularly (every 50k miles, odd coincidence), and still blew a head gasket. Fella with Timothy Leary avatar…

 

Ok, but it helps to at least work on getting the broad strokes right, so that people reading are not rendered less able to understand the issues.

 

And the simple, uncomplicated solution: clean it. Say 100K miles at the latest for first cleaning, and 50K thereafter.

 

And especially if by "it" you mean the intake manifold, which is easy to check and to clean, and is the only place the issue described in the portion you quoted can arise. And has to be physically checked now and then, because the car's monitoring is blind to that issue.

Not that I oppose cleaning the rest of the system, but it's a lot more work, and a person might choose to schedule it based on the monitoring done by the car.

 

While some of us enjoy your in depth analysis of why Gen3 engines fail early and often, there's plenty that don't have time to read your work and don't understand why you're so contrary about popular opinion. I like reading what you write, but in the back of my head I keep saying, I don't understand why he's gotta sit on top of this spiky fence for so long?

 

The little bit that you quoted kinda sums it up.

Some people want information in depth, some would rather skim, but even those who'd rather skim are probably still hoping to find simplified information that's good enough they won't have to unlearn it later if they decide they'd like to understand the stuff a little better.

 

Most don't care how or why their car got broke... They just want to get it fixed...

 

That, if true, would make this entire thread of no interest to most.

 

PriusChat addicts aren't most people...