Quote:
Originally Posted by PhaseP
Head is aluminum, anything bolts to head (except magnesium valve cover '06 year valve cover bolts) are steel.
Oil filter housing bolts onto to the head, uses steel bolts.
Vanos solenoids bolt onto the head, they use steel bolts.
Intake manifold bolts onto the head, steel bolts.
Alternator bolts on to the magnesium outer jacket of the block, it uses aluminum bolts. Starter same, aluminum bolt. Knock sensors same, aluminum bolt and so on. Oil pan bolts on to magnesium bed plate, aluminum bolts. Accessory belt tensioner bolts onto the front outer part of engine, which is magnesium, aluminum bolt. The accessory idler pulley bolts onto the alternator, if my memory is correct, steel bolt, since alternator is aluminum itself.
Engine mount support brackets bolt onto magnesium outer jacket again aluminum bolts.
It is not arbitrary choice.
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Thanks for the detailed explanation. Makes sense. In summary, it is magnesium that does not play nice with steel whereas aluminum has no such issues.
I personally don't like aluminum bolts particularly because of their single-use torque-to-yield type of usage. I always end up slightly under-torquing them (the degree/angle-torque part) because I am paranoid about snapping them. They also feel like cheese to me. I know, I know there are legit reasons like you said.