Two Subarus - common oil? HPL, intervals?

[MDN]

What are you optimizing?

For a second I was thinking since the power and hence cylinder pressure and rod bearing loads are so different between them, I could use a thinner, lower HTHS oil to have better low temperature startup wear. Then I thought about it longer and since the primary thing I would like to experimentally do is see if I can get any of these Subie blocks to (relatively) happily go 300k and that would be best served by at least 3.5 HTHS oil, I’m pretty sure. And I wasn’t gonna find 20 grade oil with that.

So I’m not optimizing now after all.

 

[scrllock]

For a second I was thinking since the power and hence cylinder pressure and rod bearing loads are so different between them, I could use a thinner, lower HTHS oil to have better low temperature startup wear. Then I thought about it longer and since the primary thing I would like to experimentally do is see if I can get any of these Subie blocks to (relatively) happily go 300k and that would be best served by at least 3.5 HTHS oil, I’m pretty sure. And I wasn’t gonna find 20 grade oil with that.

So I’m not optimizing now after all.

HTHS is unrelated to low temp wear on startup. For very cold conditions, a 0W would be desirable but in a boxer motor, you really want protection on the upper part of the piston/cylinder wall. Moly, esters, and ZDDP all help with keeping a chemical layer on those metal surfaces. 0W is also helpful once you have oil pressure, but on the first stroke you won't have any.

 

[kschachn]

HTHS is unrelated to low temp wear on startup. For very cold conditions, a 0W would be desirable but in a boxer motor, you really want protection on the upper part of the piston/cylinder wall. Moly, esters, and ZDDP all help with keeping a chemical layer on those metal surfaces. 0W is also helpful once you have oil pressure, but on the first stroke you won't have any.

Plus the fact that at startup what you're concerned with is pumping and cranking, not wear. All oils are far too thick at startup. Unless you're starting at -35 or below an oil with a 0W winter rating may be more viscous than one with a 5W rating.

And startup is not the primary source of wear.