Pistons washed...

1 and 4 are steam cleaned. It can be several cylinders.

The egr cleaning is always a waste of time if you don't have egr codes.

 

You did the EGR cleaning way too late. You’ve had protracted run time with partially clogged EGR system, head gasket’s starting to let go, and now you clean the EGR. It’s illogical to think that would somehow fix the head gasket.

 

If the above is the worse you get I would not worry about it. Generally the hg rattle is more severe and several seconds longer. However warm starts are usually good even when a severe rattle has previously happened. The engine is ready to blow a hole in the block when it happens at stop lights, eg engine offs while in Ready. By then a hg alone is a waste, an engine is the right answer.

A gen3 head gasket fail is almost never associated with an overheat and is clearly a multifactorial design flaw resolved with the gen4 redesign.

Obviously any car with an aluminum engine will blow if it is overheated. The few gen4s with a hg problem are caused by an overheat caused by an exhaust heat recirc coolant leak into the exhaust.

When it comes to overheats, too many people drive them with a warning light or a warning light that flashes and goes away. Toyota finally came to that realization later and added a temperature gauge on some hybrids.

 

No you can't just change the head. Most of the gen4 cylinder cooling improvements are in the block. The cylinder cooling was dramatically changed including a special insert in a slot around the cylinders to even out cylinder wall temps.

Gen4

Plus a new large volume egr system with exhaust picked up after the cat instead of before as in a gen3.

Toyota also updated their gen3 head gasket with more of the black sealer on the metal hg.

Some have retrofitted a gen4 engine into a gen3 but it is a frankengine with gen3 egr, intake, exhaust along with slight wiring harness mods and completely custom aux cooling circuits with frequent overheating complaints.

Others report success with used in Japan JDM gen3 engines which fit properly and are advertised as low mile. It is interesting the 2017 gen3 Prius v was still sold in Europe and Asia until 2022. Those engines could start showing up as JDM imports.

 

While I don't think the gen3 cooling system capacity is an issue, I still monitor it and have for many years.

P10 Obd2 Display


The best thing with this kind of display is you can set an audible alarm lower than the factory 248f. I have it set to 220f because I have never seen high load temperatures over 210f. Normally in 100f ambients with full ac it might be 195f.

Some have had issues with obd2 devices like Scanguage impacting other can bus traffic or bluetooth scanners causing excessive parasitic draw. I measure 6 ma draw while running with this model (newer models are available) and zero incremental when off. Your experience could vary but I like the lower temp audible alarm.

I also display accurate mph speed with a 78 mpg audible to avoid freeway tickets.

 

When it comes to egr valves, Toyota has an updated version for gen3 which may reduce stuck open valves causing low rpm stumbling and codes.

This real egr issue is easily tested without disassembly other than two easy bolts
Car care Nut Egr video with block tube test

The updated egr valve includes an ecu software update which is also recommended with their revised intake manifold.

Egr valve updated Kit 04004-58137 with 25620-37120 Updated egr valve. The kit includes the valve and gaskets at less cost than the valve alone.

Aftermarket egr valves often code right out of the box.

Some speculation was fueled by a European recommendation to change the valve and ecu software to improve hg problems. There is no corresponding recommendation from Toyota USA but several of us have the revised valve or at least the latest ecu software.