Low Ash Oils

[Dale_Knight]

Other than for natural gas burning engines I don't see a lot of information about low ash or zero ash oils. What is it about gas engines that require low ash oils and and if it's required for those would NG oils also be effective in gasoline engines. Looking at data sheets of synthetic NG oils such as Mobil 1 Pegasus or Amsoil ANG and from the small amount of data given the oil viscosities look similar to 0W40 oils but for some reason the HTHS numbers and other info is left out. The Amsoil 4-ball wear test number of .35 for the ANG looks impressive.

 

[digitalSniperX1]

Interesting question that I'll add to if you don't mind...what oils designed for gasoline engine are also considered low ash? Does lower metal content such as calcium translate to low ash?

 

[FrankN4]

I think in PCMO's, the ash they are talking about is sulfated ash. I know little but have read that higher ash amounts can cause engine deposits and maybe sludge. I know that sulfated ash helps to increase the TBN of an oil.

Where the crossover between low and high ash content is, I really don't know. Valvoline Synted list their ash below 1.0 at .90. Mobil 1 seems to run from about 1.0 to about 1.36. The Mobil 1 oil that I have used in my Toyota truck for 300,000 miles and my Chevrolet Cavalier for 200,000 miles is the highest sulfated ash oil Mobil 1 makes at 1.36 and I have seen no ill results of any kind and definately no sludge so 1.36, or less, must be acceptable.

 

[glennc]

At least some of the ash is a byproduct of the breakdown of some of the additives. ZDDP, for example, which is a multi-purpose additive that eventually breaks down partly into the sulphated ash that is being discussed. In fact, as I understand it, the purpose of the ZDDP molecule is to break down at the right temperature (high, caused by friction upon the breakdown of film lubrication, but not too high) to release sulphur, which is actually the active anti-wear component. The sulphur then combines with other stuff to create the sulphated ash.

So more anti-wear = more ash. Too much ash is bad, makes for deposits in the wrong places. Like a lot of things in oil, it is a matter of balance.

You often hear about "ashless" additives. So far nothing exists that can really replace ZDDP, though: ashless additives can supplement ZDDP but not take its place, yet.

 

[MGregoir]

They have extremely low TBNs which make them unsuitable for automotive use. There is little to no soot or acid byproduct from natural gas combustion unlike diesel or gasoline engines.

These are typically in engines with large oil capacities run at a constant temperature in constant duty. They want low ash content to reduce deposits and protect the $25,000+ catalysts used on many engines.

Mobil Pegasus 1 is 15w40 rated, but has no VIIs. ANG is similar.

HTHS is 3.7 minimum, probably closer to 4.2.

There's a wide variety of oils available, where I worked they used Petro-Canada Sentron LD 500 and Sentron 470, which were straight-40 Group III based oils. Most engine oiling systems had 110 or more gallons of capacity with a lubricator to top off the oil level and keep the additives up, as well as a variety of different sized absolute bypass filters and a centrifugal filter.

Oil change intervals factoring in top-offs/consumption are approaching 10,000 hours.

Typically, the condemnation limits for the oil are based on thickening out of grade. Straight 40 is almost universally used.