Considering Head gasket replacement - 2011 Prius - 215k miles - P0303 misfire

If you are going to replace the pistons/rings, and or rods, you'll need to pull the engine.
You might consider a short block.

 

Cylinder 2 is the most common code I think for HG. In my opinion open deck engines like this should be swapped out for a lower mileage short block or complete engine from supplier that can supply that reasonably

 

Some people have done head gaskets or subsequent timing fixes several times before realizing a bent rod mandated a replacement engine.

 

I doubt you have a bent rod, but it is a slim possibility. If you're really concerned about it, you could pull the plugs, put a slim rod through the spark plug hole, rotate the engine by hand, and mark the highest point it reaches with a line. That line should be the same for all cylinders.

However, if you're burning 1qt of oil every 1,000 miles I would not just replace the head gasket. I would pull the engine & disassemble the bottom end because it is likely to be carbon fouled. It is possible to do this in the car, but it doesn't save you any time and would be a lot more of a hassle. Plus you will probably want to hone the cylinders and install new rings and you'll get better results taking the block to a machine shop than trying to use a ball hone on a drill at home.

 

Are you loosing coolant? You "may" not have a blown gasket. Or a bent rod.
As was stated, pulling the plugs and marking a rod with each piston at tdc can tell you that.

If you catch it early, as it seems you have, minimum risk of a bent rod.

If you have not cleaned the egr system, Most importantly the cooler and intake manifold ports, that would
be your first step. That will reduce back pressure and reduce the chance of damaging the head gasket.

How do you drive? That will effect oil consumpsion. I keep it 65mph and under and ony use 1.5 qts with
10,000 mile oil changes. If I drive 70 more, than it goes up to 2-2.5.

 

Are the missfires gone? If so, drive it and keep an eye on the coolant.

 

A new short block (everything from the head gasket down, may require some swap-over of bolt-on items) would be around 2 grand USD. Someone here posted link to rebuilt blocks for around $800. I’ll see if I can dig it up.

Addendum: don't have direct link to the particular block for sale, but it was on this site:

Mag Engines – New/Reconditioned Engines Expert- All Kinds of Automotive Spares – Trusted Name in Auto Industry

 

Time to check the #3 injector. You could switch it with another cylinder.
If if moves, you know it's dirty, or bad.
But also check the wiring...

 

If you do it right and don't have a warped head you will be fine for a year or two. It will still burn oil at an excessive rate, further generating carbon which caused the oil burning and head gasket failure in the first place. Diy attempts frequently have trouble with the engine timing which requires about 75% rework to try again.

Your car ran 11 years and 200k miles before the head gasket blew. Would it be possible to repeat that duration after your repairs? Changing the piston rings, valve seals and machine shop verification of the head can get you many more years on the engine. The head gasket problems usually show up sometime after 150k when the engine is new. Your piston rings, valve seals and gaskets along with your gunked up head, intake, egr and pcv are keeping you from a reliable engine going forward.

 

If you're doing a head gasket, you might as well replace the valve stem seals. They come with the head gasket kit and you can get a loaner spring compressor from AutoZone. You might as well clean your valves with a wire wheel too.

But valve stem seals don't cause 1qt per 1,000 miles oil consumption. That's going to be carbon-fouled oil rings and plugged piston oil drain holes. Some Gen2 & corolla/matrix folks have had good luck with various flushes and ultra-short oil change intervals with detergent-heavy oils. Others use DMSO ( Ultimate engine flush process, part 1. | E46 Fanatics Forum )

 

If you do all that, haven’t got a bent piston arm, and keep up the EGR cleanings (say every 50k, I doubt you’ll have subsequent head gasket problem, but the oil consumption will persist and the catalytic converter code is worrisome.

 

Before you tear into the engine, you might want to figure out why cylinder 3 is misfiring. It could be a leaking head gasket- but that usually begins as a miss only for a short time on cold start. The engine runs better after warming up. As the problem gets worse, coolant loss and overheating occur. If alot of coolant gets into a cylinder, then you can bend a rod.

However, there are many other causes for a single cylinder misfire. Fuel injector (or wiring) fault, loss of compression (piston ring or cylinder - maybe a valve problem), ignition problem, etc. Vacuum leak at the intake manifold near #3 injector.

Side note, most EGR problems should not affect the engine at idle- the EGR valve is always closed then. If the valve is stuck open, the ECM should set a code for that.

This can be tough to figure out, but just jumping into a repair "blind" has not much chance of fixing the problem.

Sure, I might throw plugs and coils at a miss but a H/G? I would want some confirmation first.

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Just chiming in to make sure that you're including the intake manifold ports when you say you cleaned the whole EGR system.