I've got Amsoil euro 5w40 oil in my Saab 4 cylinder turbo (haven't done a used oil analysis yet). The other option per the owner's manual is 5w30. The pertinent specs are:
5w40:
HTHS 3.8
NOACK 10%
TBN 8
5w30:
HTHS 3.6
NOACK 7.1%
TBN 8.8
Most of my driving is around town, not too stressful, but some high speed highway road trips, some stop-and-go traffic, and some spirited driving. It looks like the 5w30 is the better choice, but how important is the slightly lower HTHS? Would 5w40 give a bit better wear protection? As for the 5w40, with summer heat (Maryland, so temps in the 90s are typical), would the higher NOACK of 10% and lower TBN be of concern (or would a shorter oil change interval take care of that)?
Thanks in advance
5w40:
HTHS 3.8
NOACK 10%
TBN 8
5w30:
HTHS 3.6
NOACK 7.1%
TBN 8.8
Most of my driving is around town, not too stressful, but some high speed highway road trips, some stop-and-go traffic, and some spirited driving. It looks like the 5w30 is the better choice, but how important is the slightly lower HTHS? Would 5w40 give a bit better wear protection? As for the 5w40, with summer heat (Maryland, so temps in the 90s are typical), would the higher NOACK of 10% and lower TBN be of concern (or would a shorter oil change interval take care of that)?
Thanks in advance