Sulfated ash?

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Nov 15, 2002
You usually only see the sulfated ash content given for HD fleet and diesel engine oils, but what is this number telling you as far as the performance of the oil is concerned?
Sulfated ash is an indicator of how an oil will affect valve and piston deposits as well as oil consumption. A sulfated ash limit of 1.0 mass percent was historically suggested as a maximum for optimum valve and piston deposit and oil consumption control. This was primarily driven by Detroit Diesel 2-Cycle Engines that experienced problems with oils that had greater than 1% ash. That issue has gone away and most heavy duty engine oils are about 1.3% sulfated ash. Their additive packages are driving this higher ash level. Basically, the higher the TBN (total base number), the higher the ash level. TBN is important to heavy duty diesel engines, especially now, because of the sulfur in the fuel (albeit reduced from earlier levels) and the growing use of extended drains of 30K, 40K, 50K, or even 70K miles and more. None of this really comes into play with a passenger car motor oil but for reference, the sulfated ash of a typical passenger car motor oil is anout 0.7-0.9%.
Originally posted by 68redlines73: Basically, the higher the TBN (total base number), the higher the ash level.
I hereby grant life to this long dead thread! Does this mean that the higher the sulfated ash, the better the oil's add pack, so long as it is kept below 1.4 to 1.5?
Thanks for brining this one up from the locker. I'll add to the question with "How can you estimate the sulfated ash from an elemental analysis ?' I've seen a few guys on the board (you know the two) predict it to within .1 of a percent.
The VW oil specs for gas and diesel engines which I'm familiar with mandate sulfated ash content to not exceed 1.5%.
Originally posted by ajwan: What are the benefits and costs of running a diesel engine oil (eg. Esso XD-3 0w30) in a gasoline engine (eg. Acura RSX Type-S)? Regards, Ajwan
Good HT/HS rating, strong add package, high detergency to keep your engine spotless. Esso 0W-30 should give good cold temp. performance. As long as you aren't burning large quantities of oil you've got nothing to worry about!
Sulfated ash is purely a lab product, not an engine product. It is created by adding sulfuric acid and other reagents to oil, baking it, and more steps. The ash mainly comes from the metallic salts used in detergents. Not all ash is equal. Magnesium detergent compounds leave an ash that is non-oil soluble and abrasive. Calcium detergent compounds leave an ash that is oil soluble, soft, and fluffy. A higher ash level from calcium compounds causes less engine wear than a lower ash level from magnesium products. Ken
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