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I may have to replace the head gasket on my 2L at some point and I like to plan far in advance so I started reading up on it in our repair manual. And then things got weird.....

Yes this is about my other thread with regards to the coolant contamination but not really getting any responses - probably because that's about the coolant. furthermore, some of you may find this one interesting.

Normally when replacing a HG the flatness and surface finish of both mating surfaces (head and block) is of paramount importance. Ideally the flatness variation should be no more than 0.003". This is something that is specified by manufacturer in the repair manual normally.

Except for us it is not.

I thought maybe this was an error so I started broadening my search. If you look into the 2019 (next gen, still same motor) there is still no specification. I also managed to get the instructions for a 2016 CX-5 with the 2.5L (as we know very similar). Still, no specification.

I'm quite confused by this one. It is obviously not an error at this point.

Now if you take a look at the gasket itself it's not a traditional design: Gasket - Engine Cylinder Head Gasket | Mazda3 Sedan & Hatchback (2012-2017)

Note the black sealing material. Could it be that they've designed the HG in a way that surface flatness is not so critical that it doesn't have to be considered?

This is hard to believe since both our head and block is aluminum. If overheated, aluminum tends to warp. With both in question, the chance for a new HG not sealing correctly is very high. Or at least I'd think so.

Not sure what to make of this one.
 

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Seems to me that couple of additional checks are absolutely needed if u do a hg change: i) pressure test for cracks; and ii) check line bore for camshaft journals. Head Refurb people can clamp the head against a sealing plate to do a pressure test, NP. Line bore test is done I think by removal of all finger followers bearing on the lobes... and then checking for both free rotation and by plastigaging each journal.
 

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2012 Mazda 3 GX MT5 non sky
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I have read , that on especially the 2.3 L , rear main seal is the culprit on leaks .Mazda oem is great.
Have you considered going to a Supertech gasket. I think this what is going on my engine rebuild.
 
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