Sulphuric Acid in Motor oil

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I always thought the base number was the measure of how the oil was setup to handle acidity, for example the base number of new Chevron Supreme is 7.1 and the Delo400 is 11.3. (Delo being made for diesels would compensate for extra sulfur in the fuel...)
Ph is neutral at 7.0 and VERY acid down near 1, alkaline (basic) near 14. When the base number degrades down to a low number, it is time to change oil because now the number (ph) is getting too acidic (and acidic means that the metals start seeing corrosion..). That is the main reason that I consider the 3k oil change a good thing,,,,filters can't take out acidity. Newer oils (SL) probably handle acids better than older ones did though, probably do last longer, but I change at 3k anyway.
As for the answer to your question, which componant compensates for the acidity? Someone else on here will have to answer that one. From a chemistry point of view, whichever additive it is that compensates for acidity would be called a "buffer". From what I have read elsewhere, the detergent would be responsible for the most part.

[ July 20, 2002, 07:20 PM: Message edited by: ZR2RANDO ]
Bob, I think you need to restate some of the above statements. If you want to generalize what counteracts the effects of acids in the used motor oil,,,"the detergents do it",
if you want to get specific, we need to show some reactions.
TBN is not the pH, but the reserve available to control it (calcium is the most common anti-acid). You will see a lot of opinions on what low level limit is safe. Personally I don't like to see it drop below 4, but it takes a lot of raw petroleum or poor diesel fuel to take it that far if you start with 11 or so with a decently balanced formulation. There are formulations where it depletes more rapidly than others.

[ July 20, 2002, 08:41 PM: Message edited by: widman ]
When you get blowby of combustion gases that contain sulfur and it mixes with water, we get our sulfuric acid. A diesel would have a larger problem with this if it was using high sulfur fuel. One ironic thing is that sulfuric acid will eat/react with carbon, so in theory if you had enough soot/carbon in the oil, the acid would neutralize that component, but would still be left to cause a corrosive action on other metals ect.
So normally we see a higher concentration of calcium carbonate in diesel oil, to neutralize the formation of sulfuric acid.
This a small portion of the acidic problems in oil. There are numerous acids that can form.
Formation of corrosive acids are caused by short trips, oil cannot burn off the moisture, so we get our chemical reaction, or condensation in general.
Another way to prevent acid problems is to keep the water/condensation out of the oil.
I think Johnny answered this best, Calcium.

Originally posted by satterfi:
Magnesium is also used and to a minor extent boron.

Who are you calling a boron??
It is usually the detergent additive that carries the "BASICITY" of the additive package. Acidic bodies that may be present in used crankcase oils from oxidation and fuel combustion "blow by" products are neutralized by a BASIC detrergent.

The way to achieve a BASIC (as opposed to an acidic) detergent is by heating oil souluable sulphonate or phenate with a high proportion of metallic base in the presence of a catalyst. A catalyst is some material that speeds up or helps a reaction.

Calcium, magnesium, and other metals are often used in the detergent package to increase this BASE property. In some literature, this detergent is called a "metallic soap."

Some of the newer ashless detergents are copolymers of lauryl methacrylate reacted with diethyl aminoethyl methacrylate.

The measurement of TBN, or reserve alkalinity (in the acid fighting detergent) is determined by measuring the amount of Potassium Hydroxide in the oil.

The ratio of thousandsth of a gram of Potassium Hydroxide/gram of oil, determines the percentage or parts per million of the reamining Potassium Hydroxide, or KOH.

Often stated as mg KOH/g or as a percentage of this ratio.
Total Base Number (TBN) the quantity of acid, expressed in terms of the equivalent number of milligrams of potassium hydroxide that is required to neutralize all basic constituents present in 1 gram of sample. (ASTM Designation D 974.)

From the fleet sub manual

7. Acidity or neutralization number. The neutralization number test indicates the amount of potassium hydroxide, in milligrams, necessary to neutralize one gram of the oil tested. It is, therefore, proportional to the total organic and mineral acid present. The results are apt to be misleading or subject to incorrect interpretation, since the test does not distinguish between corrosive and noncorrosive acids, both of which be present. The chief harm resulting from the presence of organic acid, which is noncorrosive, is its tendency to emulsify with water. This emulsion picks up contaminants and is a sludge which may interfere with proper oil circulation. The neutralization number of new oils is generally so low as to be of no importance.

Originally posted by VaderSS:
Total Base Number (TBN) the quantity of acid, expressed in terms of the equivalent number of milligrams of potassium hydroxide that is required to neutralize all basic constituents present in 1 gram of sample. (ASTM Designation D 974.)

I had read this before and lost it, thank you so much for looking it up.
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