4th Gen Head Gasket Replacement Experience

Ok headgasket replacement job is all done and glad it's done with! It took a total of about 35 hours which is 3x's what it would have taken a seasoned Prius mechanic to do the job, but thankful overall to have it done and had a great learning experience, and a few scared moments. I've bypassed the heat exchanger already and have taken it for several test drives.

I did have a blunder and that was I forgot to tighten down the camshaft position sensor on top of the valve cover and got a number of codes including P0340. It wasn't running well and seemed like the HV battery wasn't charging. So I ended up removing the variable VVTI sensor (left/front of valve cover), thinking it was the camshaft position sensor, and blew it out with compressed air. Upon startup, there was a whole lot of chatter and I thought the timing chain skipped a tooth. Well next day, I realized the camshaft position sensor is on the other end of the valve cover (right/front) sure enough the bolt wasn't on there, so I installed the bolt and whola, problem solved.

I actually couldn't find a video for a 4th gen HG change, but did watch a number of video's on 3rd gen Prius HG replacement and this is the best one and most concise one I found by GasketMasters which I followed:

Most of the steps are the same from 3rd to 4th gen aside from the inverter needed to be unbolted and pulled with bungee cords as far as it goes to the right side (driver's side) to access the EGR.

A few pointers from working on a 3rd gen and this one (4th gen) is:
- To remove the water pump, engine mount needs to be unbolted and engine raised about 2". Use jack with small 2x4 wood under oil pan. Use a 4th gen WP, and not a 3rd gen. Reports of problems with using 3rd gen one.
- Use new OEM toyota cylinder head bolts.
- Replace the following while at it: water pump, thermostat, spark plugs, pcv valve, air filter, ...and use all OEM Toyota parts, but for the headgasket use FelPro.
- order all parts ahead of time to keep downtime to a minimum and keep dust/rodents/creepy crawlers out of the engine and parts.
- Check to see if piston rods are bent. Turn engine and make sure pistons 1 & 4 come all the way to top evenly. Then test pistons 2 & 3 to make sure they both come up to the top evenly. Gasketmasters has a youtube video on this.
- Disconnect both HV and 12v batteries.
- Be sure to check that the camshaft rockers, rollers, valve caps are positioned properly before and after tightening down the camshaft rack. I decided to double check, and sure enough one of the rollers fell off it's track! This can be catastrophic.
- Double check all wiring harnesses and hose clamps are on.
- Have cylinder head resurfaced and leaktested.
- Flush coolant and radiator out well.
- Inspect and clean out EGR.
- Inspect for warpage on the block and head (something like this: Amazon - POWERTEC 71213 Anodized Aluminum Straight Edge Ruler | 18" | Metal Straightedge Machined Flat to Within 0.001”) and .004 feeler gauge. Use BOTH sides of the straight edge. One side may not be true as the other.
- Initial oil change at 100 - 300 miles as there's still coolant and debris from HG leak/job.

 

Yes I'm quite sure the cause was a failure in the exhaust heat exchanger as there were signs of coolant leaking out of the exhaust...gurgling sound, white smoke and coolant smell from the exhaust.

This caused the usual chain of reactions ... overheating the engine and a weakening of the HG.
Mileage is 265k.

Another cause I believe is the high mileage and the constant on/off of hybrid engines creating thermal expansion/cooling.

Maybe an oil catch can (OCC) would have extended the life of the HG, or spark plugs being changed on a more timely basis, or using top-tier gas such as Chevron.

 

Yes Mike, here's some more details on moving the inverter from my other post: Removing EGR Help Please | PriusChat

The trick on getting the EGR off is to loosen the inverter so you can lean it over and get the clearance you need to get to the 12mm bolts and 8mm reverse star bolt. I ended disconnecting the 2 big plugs in the back, 2 on top, and removed all the mounting bolts except for the 2 front ones so the inverter won't side down. Be careful not too move the inverter around too much as it has very short wires (6") running to the motor just underneath. Be patient as it's a lot more work than a gen 3.