Magnesium in HDEO bad for gas engines?

[njohnson]

Hello all,

After doing a lot of reading on here I thought I finally decided on what oils to run in our vehicles and machinery. I had settled on using Shell Rotella T6 5W-40 because of its reputation for being a stout, robust oil with good results in used oil analysis.
Then, I just read how Shell is playing around with their oils, lowering the calcium and boasting the magnesium. I just read where someone said magnesium isn't good for gas engines? If this is true, why does Shell label their HDEOs for SM specs?

I'm not trying to start an argument, just trying learn here. I thought I had found the answer to my oil needs in Rotella T6, now I need help.

Is magnesium bad for or does it do any harmful to a gas engine? Thanks.

 

[JHZR2]

I believe Mg deposits can be seen in certain engines. Somewhere on here it was discussed and I think there were even valve pictures with these.

 

[electrolover]

i thought they just used it because calcium counteracts zinc??
alot of people run rotella, i would not worry

 

[Michael_P]

I have heard by an engineer that moly in oil breaks down magnesium in short order. Don't know anything else about mag, but though I would add a question before someone effectively answered the question.

 

[The motor guy]

Originally Posted By: electrolover
i thought they just used it because calcium counteracts zinc??
alot of people run rotella, i would not worry


magnesium is a detergent. They lowered the calcium levels (also a detergent) and added magnesium to makeup for the lack of calcium.

 

[Michael_P]

So if I used this in my oil lamp, would I have a bright white flame?

 

[chubbs1]

While it is kind of unnecessary to use an HDEO in many Gas engines as long as it shares a DUAL RATING by the API it is OK to use. Some gas engines I would use them in were Volkswagon DI, Subaru's tend to do well, trucks that are going to tow heavy loads etc. If you don't need an HDEO it isn't going to make your engine last any longer than a PCMO...IMO...LMAO

 

[A_Harman]

Metallic-based detergents (magnesium) in motor oil can lead to more ash deposits in the combustion chambers and exhaust valves. This can be a problem if the engine has a problem with oil consumption down the valve guides or past the rings. More ash deposits in a gasoline engine means more possibility of detonation or preignition. If your gas engines do not have problems with oil consumption, this should not be an issue.