EGR Valve and Head Gasket failure

PriusChat has several much stronger believers in that proposition than me, but if I'm able to somewhat fairly present the best of the motivation that's been seen, there's some theoretical and some circumstantial.

The theoretical bits kind of go this way, starting with the best-supported:

• The purpose of EGR is to reduce peak in-cylinder temperatures and pressures that are hit during the power stroke, by spreading the burn over a longer portion of the stroke. This much is uncontroversially true. The magnitude of the effect is enough to reduce the formation of NOx (agreed, because that's why it's done). I have never seen any of the strong believers supply information on how that compares to the temperatures or pressures that head gaskets can withstand.
• When EGR is working, the ECM can safely push some engine parameters like ignition timing further than it can get away with when the EGR is not working. The ECM runs regular EGR flow tests, and if it detects a problem, it backs off on those parameters, at some cost to efficiency and power, to protect against damaging events like detonation. Because of that protective response, if there are dangerous scenarios, they are probably ones where the EGR flow is bad but the ECM doesn't know it, therefore doesn't do the protective fallback. One scenario we know the ECM can't detect is when EGR does flow but the four small passages within the intake manifold are unequally clogged. The ECM can then see an overall acceptable EGR flow (it only has one sensor to use for that), but really some cylinders get too much and others too little.
• Some of the posts on the subject have mistaken the effect on peak (over a fraction of a revolution, or some hundredths of a second) in-cylinder temperatures for a macro effect on engine temperature and have claimed the EGR is cooking the gasket by "overheating" the engine. This is getting toward the less well thought out end of the list; the job of regulating the engine's macro temperature belongs to the thermostat and cooling system, which have plenty of capacity to hold that temperature in spec whether the EGR is or isn't doing its thing.

On the circumstantial end, I've seen a bunch of posts highlighting photos of intake manifolds where the four individual passages are unequally clogged, often with the most-clogged ones at cylinder 1 and/or 2, and those posts usually also say that lots and lots of head gasket failures have been reported and they've been predominantly at cylinder 1 and/or 2.

I haven't seen anybody appearing to collect data systematically enough to answer if you wanted to ask just what "lots and lots" or "predominantly" mean. I recently saw one of the stronger believers in another post say something like "99 times out of 100" symptoms of misfiring in a Gen 3 will be a failed head gasket. I haven't, again, been able to see anybody doing the kind of recordkeeping needed for that to be anything other than the 99% of statistics that are completely made up. Maybe somebody is and I just haven't seen it.

We do also get misfire threads on PriusChat that end up being traced to any of the usual-suspect causes of misfires. A couple of those have been recent; one of them might even have been the one with the "99 out of 100" doomsaying post. I don't remember for sure.

 

You will find working Toyota mechanics who blame excessively carboned up engines in gen3 engines, including intakes, valves, pistons, egr systems, caused by a brand new in 2010 Prius 1.8L powerplant. Poor piston and ring design causing excessive blowby was rectified in a mid 2014 update. When you study the massive redesign of this engine in 2016, you get a better idea of what was broken in the earlier 2010-2015 engines.

Intakes fill with oil and condensate on gen3s and "macro" cylinder cooling is a hg suspect. Intake manifolds, blocks and engine cooling passages were changed significantly in gen4 as well. Egrs systems were overhauled as well.

When you add other design flaws like brake boosters and inverters, the gen3 Prius becomes a questionable car to buy used and often expensive to maintain especially over 150,000 miles. I would buy a 2016 or newer if buying used.

One of many gen4 changes

 

Link on how to deal with with the EGR carbon in my signature.

- A believer

 

Which is the bigger improvement, 2014 Gen3 - > 2015 Gen3, or Gen3 - > Gen4?

 

For EGR and it’s impact on head gaskets? My 2 cents: door no 2, by a landslide.

 

I think you mean ZF3, the T-CP-ZF3-A110-D warranty enhancement until 31 March 2017 (unlimited miles) then to the first of 10 years or 150,000 miles, with the repair described in T-SB-0027-16.

The problem those documents describe is the valve sticking, because of excess carbon buildup at the valve.

They replace the valve in the TSB, and there is something slightly different about the replacement valve, but I have yet to see anybody at all compare the two of them side by side and figure out what. The basic design isn't any different, it has a pintle that moves in and out when a six-terminal stepper motor rotor spins on the pintle's threads. They might have made the new one slightly larger/beefier, which would explain the slight mod to the wire harness to make the plug reach, or maybe its plug just points a slightly different way. It would be so great if somebody with access to both valves would post some detailed teardown photos and measurements.

If the old valve could be made to stick by glomming enough carbon onto it, I have no real doubt that the new one also could be made to stick by glomming enough carbon onto it. I don't think the new one has actual added magic.

I also have no real doubt that you could keep either variant of valve working just fine for aeons, doing nothing more complicated than getting the carbon out of it every now and then. I've never owned a vehicle with EGR where I didn't have to do that anyway. The one in my mom's 1979 Colt needed such attention every time we turned around.

Some time ago I bought a used valve and cooler from another member who had removed and cleaned them, and this summer I swapped those with mine (which were still working fine, though the ECM's flow monitor values were coming out a little low). The old ones are still sitting here waiting to be cleaned; I'm procrastinating on that until I have come up with a good way to bench flow test them before and after.

The used valve that I bought had probably been cleaned with some aggressive solvent like brake cleaner; moving the pintle in and out by hand felt like it had been left fairly dry of lube. I have some high-temp graphite grease sitting around and worked a little of that around the stem before putting that valve in service. It felt better after that. We'll see how it holds up.

It's been widely observed that the two Phillips screws holding the stator on the valve can be stubborn, and something like the Lisle or Thexton seized-fastener removal kits, or the sort of hand impact driver that you bop with a hammer, gets them out nice as you please.

I'd say that if you're concerned about the valve that's on your car, take it out and look at it. If it needs cleaning clean it. Take a look at your flow monitor values every now and then, and keep those four passages in the intake manifold clean. As described above, if there's any EGR-related condition that poses a mechanical risk, unequal manifold clogging is probably the top contender, because of the way the ECM can't directly detect it. As a bonus, checking and cleaning the manifold is really the easiest to do of the EGR-related chores.

There was also an ECM firmware update that would be done in T-SB-0027-16 along with changing the valve. For a long time, I assumed that must be tweaking some settings specific to the changed valve. But in a different recent thread, we noticed there's also a TSB touting a revised intake manifold, and that also included a firmware update, using the same updated version. So my current guess about what's in that update is nothing really specific to the valve or the manifold, and maybe just a better way they thought of programming the system for detecting issues or reacting more robustly.

 

@mjoo ran water through just the cooler (I believe), and measured before/after flow volumes. I’m guessing just pouring in through a funnel, for a timed interval?

 

That could be pretty easy and repeatable, but would call for being very consistent in the shape of the quart container and its height above the cooler being tested. At present, I'm leaning toward doing something with air, which might have flow properties more like those of exhaust.

 

Perhaps something like this could be rigged up to measure gross flow through the dirty and cleaned EGR coolers.

I'd definitely use some kind of filter before the meter though, because the dirty EGR cooler could pass some nasty stuff through.

Posted via the PriusChat mobile app.

 

Alternatively, one of these could be rigged up between the EGR cooler and a vacuum source.

Posted via the PriusChat mobile app.

 

The peak flow meter would be useless. The second one is definitely a worthwhile idea. The biggest issue would be if the flow rates match those of the EGR system. I suppose you could also design and build your own using whatever weights and sizes you needed. The higher the ball rises the more flow/vacuum.

 

Visual inspection too? If you look at the intake manifold, and EGR passage at cylinder one is basically a coal mine after a cave-in, that's gotta say something. Ditto for the cooler.

 

Everybody's done that. The part I'd like to add is "looks like this" corresponds to "this actual effect on flow."

Ideally we'd have multiple such pairs of data, but I'll be happy just to get it started.

If only I had a sensitive air pressure sensor and mass airflow sensor somewhere I could borrow.

 

Handheld anemometer.

Posted via the PriusChat mobile app.