Additive - detergent composition and possible effects on engine block?

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In another thread where someone was trying to get a recommendation on the options of 15w-40 HDEO to use in his volvo 850 (aluminum engine), lewk wrote: -------- "rotella has a harsher detergent(magnesium) than delo(calcium). this is something to consider if you have an aluminum block/head rather than cast iron.not sure how this would translate into wear but, milder is always a prime consideration if longevity is a factor." -------- I am curious to hear what people have to say about this. I have also heard a person or two mention a corrosion potential by using an oil that was too over based for the application, but would there be any such link with this? Thanks in advance.
 

Curious Kid

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Thanks for the link. It amazes me at just how much chemistry is going on while one's simply putting an engine to work! That's what makes the sense of having selected an ideal oil so difficult, yet the challenge so intriguing. There's always something new lurking around the corner! If a lubricant's TBN was below 12, how might the two different detergent compounds play in relation to engine's composition - like the question originally raised - is one safer to use than the other, or is there really no difference/cause for concern? Thanks again!
 
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I am in the expiremental stage of Fleet HDD's and HDEO's myself. I have heard the cons of MG being abrasive before but the fairness flaw I have makes me admit that I saw that statement repeatedly whilst people were talking down Amsoil and talking up whatever their pet oil of the time was. All detergents such as Ca or MG are are metallic salts that combine with acids to neutralize them. Dispersant keep them from clumping together. The exact chemistry of positive and negative charges at work still elludes me but I am working on it. I have heard that once Calcium has sacrificed itself it becomes a soft ash. This is where the argument concerning Magnesium comes in. It too should deteriorate when spent. I have no idea how these differing chemistries interact with indivisual metalurgy but suspect that with an all fleet motor oil we are not approaching the levels that could cause abrasive harm if there is such a thing from modern Mg compounds used in additive chemistry. What we need is a good Chemist.. Mola?
 
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sebring, florida
theres plenty of diesels with aluminum cylinder heads running around. and just about every engine has aluminum pistons, diesel or not. if magnesium was bad for aluminum parts then you would hear problems from every single person who ever used rotella.
 
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Colorado
Not necessarily. A lot of the minor issues relevant to oil won't show up for every user, or the average user, or even the 80th percentile user. Some things, like the difference between 8ppm and 12ppm iron wear or between a Pure One and store brand filter, will only be relevant in the "eventual" future for those who want to keep a car running forever. That is why I like to consider minor difference between the fluids/parts I use. - Glenn
 
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