you are not correct genuine TOYOTA 's is not aluminium
trust me (TOYOTA) on this one TOYOTA part is bakelite plastic $65 (superior version) or alloy $35 (cheaper version) . alloy is not 100% aluminium . So if you want to experiment with it and do not trust the TOYOTA it is your call . I was questioning that myself why it is plastic , Toyota told me not to mess with that part just for that reason that I said previously. Good that you are questioning and not "go with a flow"
I am definitely not a "go with the flow" type of person, but I am a person that makes decisions based on actual data, not what some guy at Toyota said (otherwise I'd believe the 200 was already discontinued, the 4Runner was going unibody in 2016, WS fluid never needs to be changed, etc.). I purchased the OEM aluminum housing on my Tundra on my second oil change after the two free ones after my first oil change on it was so difficult as the plastic housing was so tight from my first at home change change (I can see how they could break). It was a great upgrade. I did that after reading MANY different threads on a ton of Toyota members doing this same upgrade with no incident. I had that Tundra through six oil changes with the metal housing with no issues with the housing. I still have been unable to find one thread on any Toyota forum that states a member has had trouble with the oem aluminum alloy housing. I do however, know for a fact that one member on a different forum had the plastic housing break up inside the engine, and his dealership charged him a lot of $$$ to fix it. I think it happened to a member here too, but I don't remember who.
My biggest concern with a metal on metal housing is stripping the threads from crossthreading or overtightening. I'd be more concerned if I was having an inexperienced tech changing my oil. If I was going to go to Toyota for all my oil changes, I'd probably keep the plastic housing. Since I change my own, I have no concerns with this.
And while I agree that there is always an expansion concern with different metals exposed to heat, I personally do not see a huge concern between a billet aluminum housing and an aluminum alloy block.
I believe that thermal expansion of aluminum vs aluminum/magnesium alloy (what many engines are cast from) and most other aluminum alloys, in the temperature range that this filter housing would be exposed to (and even temperatures doubling normal operating temperatures) would be very similar, although at higher temperatures aluminum will indeed expand slightly more. Without knowing the exact alloy composition of the Toyota engine, exact figures cannot be determined. If someone knows the exact composition of the 3UR-FE Block and the Jowett cap I could determine the average coefficients of expansion between the two at peak operating temperature, assuming the Jowett cap is 100% aluminum. There are a lot of data tables on this subject.
However, the thermal expansion of plastics are much higher than aluminum, how much exactly I can't say because I also don't know what type of plastic the OEM housing is. If it is truly bakelite (the first synthetic plastic) I'd be even more concerned with keeping it, as I believe true bakelite is only rated to continuous operating temp of 250 degrees F. While normal engine temp is below that, going higher than that is still in the normal range. My suspicion is it is not in fact bakelite plastic, but similar but more advanced high temp, chemical resistant plastic. Whatever it is comprised of, it does seem to have thermal expansion issues, as this is probably the reason the damn stock filter always seemed to be on too tight, even after doing my own oil changes and not over torquing. On two oil changes with the Jowett, it has removed very easily with a warm engine.
