Originally Posted By: irv
If I understand this correctly, you are saying an oil requires both magnesium and calcium to ensure it it neutralizes all acids and not just some?
Good TBN retention means nothing if it is not doing it's job neutralizing acids.
Calcium neutralizes everything. Magnesium doesn't neutralize everything and for that reason it lasts longer (longer TBN retention). You need both for neutralizing everything and TBN retention. You also need to reduce calcium and add magnesium for LSPI protection. Note that type of detergent also greatly affects wear protection and they also need to test the detergent in the finished oil for wear protection.
Originally Posted By: jwa
So maybe Redline, despite it's high calcium, wouldn't dramatically increase LSPI event chances due to also having high ZDDP and moly.
Calcium is the main culprit for LSPI. ZDDP and moly help but chances are that if you have a lot of calcium, they won't help much.
Originally Posted By: SubieRubyRoo
The way I understand that is calcium does not necessarily have to be reduced... but the ratio of calcium to magnesium must be less than pre-T/GDI engines to combat LSPI.
If you add all of the factors together, I see no real reason why you couldn't still have an oil with say 2300ppm of calcium, 1500ppm of magnesium, and a good dose of ZDDP/moly. The higher magnesium and ZDDP/moly will offset the calcium. That's the way I read it, especially when combined with the fact that NOACK and viscosity are not significant factors.
Maybe SOJ will weigh in.
Again, calcium is the main culprit and it seems to act as a catalyst in generating the LSPI reactions. ZDDP, moly, and lower viscosity are secondary in reducing LSPI. Regardless, you can't go bonanza on additive ppm's because of SAPS limits in any street-use motor oil.
Regarding viscosity, I noticed that M1 15W-50 is one of the very few Mobil 1 oils not LSPI-certified (not API SN Plus) -- this is why I looked up this SAE paper. Since it has little calcium and a lot of magnesium, it's either that its high viscosity is causing LSPI or they didn't bother to certify it because it's not a common viscosity grade for newer cars.