Sulfated ash is measured by treating the oil with sulfuric acid and then igniting the mixture. The residue is then measured. Oils that produce ash of 0.1% or lower are considered ashless; up to 0.6% are classed as low ash, 0.7-1% medium ash and over 1% is a high ash oil.

Engine designers have begun to look at SA as a factor in combustion chamber deposits and the precursors of emission problems. The presence of more than the optimal amount can cause excessive deposits on various parts, which can result in reduced heat transfer, pre-ignition or detonation, or both, ring sticking or breaking, plug fouling, and valve burning. This became a focus during the development of CJ-4 oils for diesels which requires low ash content to assist with the efficiency of after treatment emission systems (DPF AND SCR systems). These systems rely on clean burning in combustion chambers to minimize harmful emissions. It is not surprising that this will affect gasoline and direct injection engines in a similar way, with medium - low ash oils being preferred by engine manufacturers in these cases.

It will be interesting to see what develops in terms of ashless detergents and how they are applied. Various types of calcium sulfonate is one of the most commonly used detergents in commercial additive packages, and removing them could cause many formulators big head aches. The difficulty is that detergents prevent sludge and varnish in the crankcase, but when burned in the cylinders or when experiencing blow-by it can cause deposits. The presence of these detergents is usually identified by the calcium number found on your UOA.

"Thanks for your message, Mike. We appreciate the feedback. A slight reduction in ash is desirable for advanced engine technology such as gasoline direct injection (GDI) engine and passenger car diesel engines. With GDI engines, higher levels of ash appear to result in a higher occurrence of Low Speed Pre-Ignition. The industry is currently developing tests and specifications to address Low Speed Pre-Ignition. In the future, passenger car engine oil specifications such as ILSAC GF-6 and dexos1 (next generation) are likely to have requirements such as lower ash to address Low Speed Pre-Ignition.

As for TBN retention, it is only a single parameter that provides an indication of the used oil condition. A reduction in TBN is an indication that the overbased detergent is doing its job by neutralizing acids that form as a result of combustion. TBN should be used in combination with other used oil parameters such as oxidation, nitration, TAN (Total Acid Number), ICP metals, D4684 MRV viscosity, and D445 kinematic viscosity to determine the overall condition of the used oil.

Finally, in our experience in severe-service Las Vegas field testing, Mobil 1 engine oil TBN levels typically do not drop below 2 for vehicles with 15,000 mile oil drain intervals. Furthermore, it is our experience that those oils tend not to drop any lower when we continue to 20,000 mile oil drains.

We hope this information was both helpful and informative. Thanks again for reaching out, and for your continued support of Mobil 1."