Low Calcium Motor Oils...

Would a D1G2 engine be harmed if a 5W-30 C3 D2 is used in it? Somebody here can advise me on this. So, thank you.
And the emphasis should be on the fact that this is a DI phenomenon, a conventional port injected engine operated in the same manner does not experience LSPI.
LSPI is characterised by igniting before the spark plug fires so pulling timing doesn't work, don't see why port injection would be immune?
Coincidentally M1 0W20HM is thicker than the 5W at operating temp. It makes the 5W look redundant. I can't speak to viscosity stability between the two. Maybe the 5W is thicker after a while than the 0W.
Probably due to a higher level of added Viscosity index improver.
LSPI is characterised by igniting before the spark plug fires so pulling timing doesn't work, don't see why port injection would be immune?
There are plenty of articles about this, from literally every major motor oil company and additive suppliers.
LSPI is a recent phenomenon that began occurring in mainly Turbo GDI engines. Some naturally aspirated GDI engines have had the issue as well but much less common. Maybe you’re confusing LSPI with pinging, which is caused by an artificially raised compression ratio due to combustion chamber deposits, or wrong octane fuel being used.
No, I know the difference, the part I have trouble with is that it's an exclusive GDI problem. Granted that GDI engines are more prone because they push the power density in those engines further. That's the whole reason they went with GDI in the first place. And the articles I've read agree with that, it's not exclusive to GDI.
LSPI is characterised by igniting before the spark plug fires so pulling timing doesn't work, don't see why port injection would be immune?

It's a problem that arrived on the scene with TGDI, and all of the mechanisms to mitigate it came about after that. It wasn't a problem with port injected engines.

It's "super knock". You take a higher static compression ratio boosted engine that's direct injected and the mixture may auto-ignite upon fuel injection before it is supposed to be ignited by the spark plug. The auto-ignition, as @stower17 noted, appears to correlate with additives in the engine oil that is present on the cylinder walls, which is why efforts to modify additive packages to mitigate it have shown to be effective. This uncontrolled improperly timed phenomenon can blow holes in pistons or crack them. It wasn't an issue with port injected engines because:

1. Static compression ratios on forced induction port injected engines can't be as high
2. The fuel is already mixed with the air on port injected, it isn't being added after the fact
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Its a GDI issue, made apparent by Turbocharging. GDI engines are able to spray fuel into the combustion chamber during different times of the combustion process due to the GDI injectors being in the combustion chamber (high PSI split injection). Under certain operating conditions, when the split injection is injected into the combustion chamber and the fuel charge reacts with oil droplets (mainly on the cylinder walls) it can create an unintended explosion.

The issue of LSPI doesn’t happen in port injected engines. The the injector PSI in port injected engines is much lower so it’s not spraying fuel on the cylinder walls when the injectors spray in the intake port.
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To add, from Lubrizol, emphasis added:

Lubrizol said:
Downsized gasoline engines, coupled with gasoline direct injection (GDI) and turbocharging, have provided an effective means to meet both emissions standards and customers' drivability expectations. As a result, these engines have become more and more common in the passenger vehicle marketplace over the past 10 years. To maximize fuel economy, these engines are commonly calibrated to operate at low speeds and high engine loads well into the traditional knock-limited region. Advanced engine controls and GDI have effectively suppressed knock and allowed the engines to operate in this high efficiency region more often than was historically possible. Unfortunately, many of these downsized, boosted engines have experienced a different type of uncontrolled combustion. This combustion occurs when the engine is operating under high load and low speed conditions and has been named Low Speed Pre-Ignition (LSPI).

And another quote from Lubrizol:

Lubrizol said:
This is the situation for drivers when low speed pre-ignition (LSPI) strikes in turbocharged gasoline direction injection (TGDI) engines. As we detailed recently, newly available lubricants certified under API SN Plus can stop LSPI before it happens. And service shops bear a responsibility to educate everyday drivers on why choosing those higher performance lubricants is important.

But there’s another layer to this story, and it’s one that isn’t fully told with API SN Plus.

The lubricant industry’s understanding of LSPI and our approaches to eliminating it in TGDI engines are still evolving. With the development of the LSPI test that helps certify API SN Plus lubricants, we’ve found one way to accomplish that goal.

That doesn’t mean there aren’t others.
Because they have a contractual relationship with Exxon/Mobil. All of their high performance cars come with Mobil 1 and Mobil 1 printed on the oil cap. And the AC/Delco recommendation is pretty obvious. That is a GM brand. The Dexos certification is given to any brand of oil that meets current GM specs. Here is a list straight from GM of Dexos approved oils. You should be able to find one from this list. https://www.gmdexos.com/brands/dexos1/index.html
I understand the marketing agreement GM has again with Mobil lubes however they also have agreements with oil manufacturers who pay GM a royalty to get the Dexos 1 Generation 2 (and beyond) license...if any Dexos 1 Generation 2 oil would work why wouldn't GM just say that...but they mention low calcium for a reason...

I had hoped someone might have a link or knowledge of low calcium oils as I haven't been able to locate that...in the interim, I will stick with Mobil 1 oil for the 2.0T...

It isn't just a high Calcium issue. More so the Calcium and Sodium ppm in relation to mitigator additives like Molybdenum and Zinc. You can have high Calcium per say if the corresponding Moly and/or Zinc are relatively high as well. This is why the specification, approvals and certifications are more important than reading VOA for specific ingredients when concerned with LSPI.
I do realize what you are saying but I'm only concerned for the time being with GM's own recommendation that a low calcium, full synthetic only be used in the 2.0 Turbo engine to avoid issues...

the GF bought her 2013 Malibu 2.0T brand new and it has only had full synthetic motor oil used except for from the factory (Dexos 1 at the time was a synthetic blend) along with using 93 octane Premium Top Tier gasoline...she has had no issues with her engine thus far but I'd like to keep it that was as the car still looks almost new and is low mileage...

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I do realize what you are saying but I'm only concerned for the time being with GM's own recommendation that a low calcium, full synthetionly be used in the 2.0 Turbo engine...

A dexos1 Gen2 approved oil will be all you need. Beyond that, if you want to find the d1G2 oil with the least Calcium, you can visit https://pqia.org/ .

But remember, the recently introduced, newly formulated API SP/GF-6 oils have not all been tested yet on that site. Not to mention motor oils go through constant formulation tweeks not privy to the consumer. This is why, again, the certifications will guide you in the right direction.
Dexos1 Gen2 oils also have to meet a spec to reduce timing chain wear, as well as mitigate LSPI. I will say again that all you need to look for is D1G2 certification, it is a GM issued cert. If your Mobil 1 is a recent purchase it should have the Dexos1 Gen2 label on the front. Use it with confidence. No need to overthink this.
I guess I don't understand why GM would tell it's own dealerships and techs to use Mobil 1 specifically because of it's low calcium and not because of it's Dexos certification...since dealerships and techs are supposed to be using Dexos certified oil anyway...why make the distinction to use a low calcium synthetic...why make a technical bulletin when you are already supposed to following the Dexos mandate already???

wemay...thanks SO much for that link...it helps a lot

okay...perhaps I get it now...if the Generation 2 Dexos 1 oil spec was made to reduce LSPI and any oil carrying the license for Dexos 1 Generation 2 meets or exceeds the standard then buying most any oil with that spec will do her car just fine...

I was spooked a bit by checking the calcium level in Shell Rotella Gas Truck and Mobil 1 oils (albeit in a different weight than I use in her car) and saw a much higher calcium level in the Shell Gas Truck...

I didn't realize that I was already ahead of where GM was using the Dexos 1 Gen 2 full synthetic before being notified about a change to low calcium full synthetic...

thanks for the feedback and putting up with me on this... (y)