Sulfated Ash, wt%, ASTM D 874 test questions

[mbacfp]

Hello all,

Quick question about the Sulfated Ash, wt%, ASTM D 874 test in motor oils. Here is a link to a website that explains the test.

http://www.synforce.com.au/sulphated_ash.html

Here is an excerpt from the test Parameters
[ASTM D 874 Test Parameters

These additives usually contain one or more of the following metals:
•barium
•calcium
•magnesium
•zinc
•potassium
•sodium
•tin

These elements can be present in combined form:
•sulphur
•phosphorus
•chlorine

The sample is ignited and burned until only ash and carbon remain.
After cooling, the residue is treated with sulphuric acid and heated to 775C until carbon oxidation is complete. The ash is then cooled, retreated with sulphuric acid, and heated to 775C to constant weight. The sulphated ash can be used to indicate the concentration of known metal-containing additives in new oils. The result to the nearest 0.001 mass% for samples below 0.02 mass% and to the nearest 0.01 mass% for higher levels are reported as the sulphated ash.]

So, basically the oil is heated and cooled, heated cooled...then tested for how much sulphated ash that is created in the oil (residue) to potentially gum up the turbo and engine? So, seems like this test implies running in engine for long periods of time before cool off helps keep an engine cleaner (less residue created by multiple cool offs)?

Thanks,

 

[SonofJoe]

In all the time I spent playing with engine oils, I never ever understood the logic or raison d'être for the sulphated ash test. It's one of those archaic tests that probably meant something once upon a time but what it was has long been forgotten. Certainly the test existed for decades before Low-SAPs oils started getting talked about.

I have a very vague recollection that the 1.5% sulphated ash limit came about in the '80s possibly as a result of spark plug whiskering but I may have that completely wrong. The limit covers all metals but I'm guessing that it was intended as a brake on the amount of over-based metallic detergent you can put into an oil. I'm curious to hear if anymore knows different.

Low SAPs oils gave the test a new lease of life as everyone worried that their Diesel Particle Filters were going to plug up with ash. Personally I always thought the case for this was always overplayed because if you design an engine properly, you shouldn't have excessive amounts of oil burning and going down the tail pipe. Interestingly, as I look at this today, I see endless reports of plugged DPF problems. However this isn't caused by ash plugging as much as by the filters failing to light-off because of short-tripping.

 

[Jetronic]

Agreed.

I've seen a few dpf failures, but it's always a result of a failed cat, or regens not taking place otherwise. Not one that I could attribute to high ash content.

 

[chrisri]

Originally Posted By: SonofJoe
In all the time I spent playing with engine oils, I never ever understood the logic or raison d'être for the sulphated ash test. It's one of those archaic tests that probably meant something once upon a time but what it was has long been forgotten. Certainly the test existed for decades before Low-SAPs oils started getting talked about.

I have a very vague recollection that the 1.5% sulphated ash limit came about in the '80s possibly as a result of spark plug whiskering but I may have that completely wrong. The limit covers all metals but I'm guessing that it was intended as a brake on the amount of over-based metallic detergent you can put into an oil. I'm curious to hear if anymore knows different.

Low SAPs oils gave the test a new lease of life as everyone worried that their Diesel Particle Filters were going to plug up with ash. Personally I always thought the case for this was always overplayed because if you design an engine properly, you shouldn't have excessive amounts of oil burning and going down the tail pipe. Interestingly, as I look at this today, I see endless reports of plugged DPF problems. However this isn't caused by ash plugging as much as by the filters failing to light-off because of short-tripping.


I have used 1.9% ash oil in two petrol engines for years without any problems (over 100k in one car). Never experienced any plug or oil related problems with that engine.

As for high vs low SAPS in engines with DPF, I agree that in most modern diesels it doesn't matter at all, well designed diesels do not consume much oil if at all.
Also, my subjective finding is that full SAPS oil will fair better by the end of OCI.

Problem would rise with use of full SAPS oils in a diesels that use oil -like over 300k cars, and TDIs. TDIs use ridiculous amounts of oil, even the low mileage ones.