Do some Serious "thinking" before you just replace a head gasket

Bent rod undoubtedly due to hydro-locking.

 

yep, its not always what you imagine it to be.

 

Did you catch it by checking the piston faces relative to top-of-block, or did it take disassemble, direct inspection of the pistons?

The smoking gun in all this, it's almost always cylinder number one. And the EGR gas enters the intake manifold from the other end.

How many miles on it, btw?

 

Yeah - I have been reading the head gasket posts as my wife's 2012 is showing symptoms. I have so far removed the valve cover, I'm waiting for the Torx socket set to remove the EGR stud(was supposed to be delivered yesterday). I have read many posts including danlatu (who also had a bent rod) and The Critic write up their experience. All the information on here has been invaluable. The first thing I'm going to check when the head comes off is make sure the pistons come all the way up, esp #1. I really don't want to take the motor out...
Best of luck - please keep us posted!

 

I'm not sure myself. I know:

1. The EGR gasses enter on the cylinder #4 end of the intake manifold.
2. The head gasket failures are usually between cylinder #1 and #2.

I can also dig up a pic of my intake manifold, soaking in the laundry sink:



While not that obvious, maybe cylinders #1 and #2 are burbling up more stuff? Not sure.

It may depend on the year too: as far as I know, earlier 3rd gen intake dump the EGR gas into a single gallery tube, and it branches off to the four capillaries, one per port. Later version, I think, the initial gallery splits into two intermediate passageways, then they in turn split into the capillaries.

It is a bit bewildering, but known items 1 and 2 above, are factors somehow. I think.

 

Thanks, Mendel! That helps. Bottom line for me is to do the cleaning.

 

I used Oxi Clean solution on the intake manifold, but you maybe want to be cautious. You can clean the IM pretty well with just Brake Cleaner (CRC brand or whatever). Oxi is very good for the EGR cooler, but maybe getting obsessive for the intake. And the downside with the intake: there are some threaded (and pass-through) bolt inserts bonded into the plastic, and if the Oxi solution is not completely flushed out, they can subsequently react with the bolts/studs screwing into the inserts.

I had my IM off a second time, recently, and noticed a white crusty build-up on a couple of bolts. I cleaned them well and applied a little anti-seize, think it's in check now.

Here's the boiler plate info on EGR and intake manifold cleaning, and some Repair Manual info attachments (torque values etc):

The simplest way to see where you're at, is to check the degree of carbon build up in the EGR pipe, a stainless steel connecting pipe between the EGR valve and intake manifold. Watch @NutzAboutBolts video #16 here:

Nutz About Bolts Prius Maintenance Videos | PriusChat

Two or three other videos linked there too, for the full cleaning of the intake manifold, full EGR clean, and Oil Catch Can install.

Good thread:

EGR & Intake Manifold Clean Results | PriusChat

Another:

Oil Catch Can, Eliminate that knock! | PriusChat

Some tools worth having:

E8 Torx socket (mandatory)
E6 Torx socket (optional, but good to have, to remove the throttle body studs from intake manifold)
3/8" ratchet wrench, regular and long handle, flex head, you can never have enough (or 1/2 plus reducer)
1/4" ratchet wrench, or 3/8" to 1/4" reducer
Ratchet extensions: you can never have enough
Long needle nose piers, straight and bent tip
Ratcheting 12mm box wrench (optional, but makes disconnection of the EGR cooler from exhaust easier)
Torque wrench (3/8" and 1/4" both good to have)
Floor jack and safety stands (or ramps): basically some method to raise front, if you need to take underpanel off, which you may need to, both for access and to recover dropped items.

 

So, can you tell if you have a bent rod based on symptoms. For example, if you have never experienced hydrolock with the headgasket issue, is there still risk of a bent rod?

 

Yes it is possible. That is why I said if "your" head gasket job escalates to an engine replacement, get new rings at the same time. A rod can be slightly bent and still run. However it will run badly in a different way than a leaking head gasket and may be noticed after the head gasket job is complete. Or the initial bent rod is very slight with minor impact but gets worse. Sometimes causing a hole in the block.

The key is your mechanic actually checking the engine for other damage after it is torn down. Too often they get tunnel vision and just change the gasket. We have seen several owners go through this three times in a row.

This video shows some of the worst case head gasket scenarios: