Pine Hollow Diagnostics does a Prius v Head Gasket

Yeah that was astounding. Some idiot put it on with an impact? Maybe been on for some time...

He seemed to have one hell of a time breaking the bond between head and block.

Don't really subscribe to his litany of likely causes, the "why it failed", but leave that for another day.

 

Doesn’t this engine use stretch head bolts?

 

There should be angle turns after the head bolts are torqued, as the bolts are stretch I looked it up. I did two 90 deg turns on my hg job on a Toyota truck. That’s a lot of turning from already very tight, and sets the bolts into the elastic zone as I understand it.
I didn’t see him do the angle turns but maybe missed it. Also you can’t just throw a gasket on a head, it has to be perfectly cleaned and measured for warping. Cleaned while maintaining flatness, not with abrasive pads to make shiny for the eyes.

 

With 3rd gen (and likely 2nd through 4th as well), after initial torque, it's 90 degrees, then 45.

 

Where’s that from? My 2010 Prius repair manual says 90, then 45. IIRC several YouTubers say sim.


Also initial torque is 36 lb/ft.

 

Ah lightbulb goes on; you’re clarifying, second Gen is 90, then another 90.

 

The 180 degrees is only about .030”. I was looking by eye at my old versus new head bolts and it isn’t very length difference much by eye side by side, head to toe. By eye the old are ok maybe, but not really. Anyway don’t know if this guy did the torque to yield.

 

Further, from my gen 2 pdf:


Again, gen 3 is 90, then 45.

 

What’s the point of a set torque value when additional turns are required?

Like the old saw, torque until bolts strip out, then back off half a turn…

 

I get that. In my experience, the desired degree of ‘tightness’ is specified via a set torque value and re-torqued to set after X hours.

 

Considering the bolts are oiled, that initial torque should tension them fairly uniformly?

 

I followed all that when I did the gasket, not wanting to have to redo the job. I just used new bolts. I did take measurements with a micrometer of the diameters, calipers for length, but nothing stood out as I can reuse the bolts. The stretch is only 3/4 mm or about .030”, so new bolts are the sure bet. This number is from the thread pitch of 1.5 mm.
Someone asked why not only torque. This is why and the head gasket is designed for stretch bolts, not just torque.

https://www.rockauto.com/info/604/24_EN.pdf