Acid Burn-off?

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Sep 25, 2002
Loveland, Colorado
Lately, my son's been wimping out on riding his bike to school ("Jeez, it's only down to 16! Wear your ski goggles!"). This means my car's getting two 2mi trips on the coldest days (my work's only 3 blks from school, so I end up giving him a ride home on those days, too). The consensus is that this is bad due to the acid formation which develops under these conditions. But, the traditional remedy is take the occassional long drive, & everything will "burn-off" & be OK.

So my questions are:
1) Do the acids get evaporated like water, or are they converted into something else?
2) Do they leave behind some portion of their components?
3) Do they end up carrying away even more things (since they're water combined with combustion by-products) than just driving out moisture would?
4) Would the next hotter plug help prevent acids from forming under these conditions in the first place?

Thanks for your thoughts on this.

(I really like this icon, even though I have no reason to use it. Must be the antlers...)
I have read that the sulphuric acids will allow the oils additive package to deplete trying to keep it neutralized. After the additives are gone the acid keeps on attacking the internal parts. Does not burn off or evaporate.

") Would the next hotter plug help prevent acids from forming under these conditions in the first place?"


[ December 09, 2002, 08:12 PM: Message edited by: dragboat ]
Hehe, I like the new smilie too!

I don't have the answers to the questions, however why not take a longer route a few times a week to ensure the engine gets good and hot? Or at least take one highway trip on the weekend, 40-50 miles should do it.
Maybe base your oil change schedule on time rather than miles. Try sampling your oil after three months of this sort of driving. That should give you some indication on how long you can keep this up before the antioxidants/TBN are used up and damage can begin.
I don't know if this link will get through or not:

Maybe those more experienced can comment - even if this is a gas engine - seems like a CI/SL rated oil and very frequent changes would be a good idea. Like every 2500 miles and/or 3 months? whichever comes first. And if the budget allows, a syn CI to help w/the cold temps
I do not think the acids will be burnt for your type of driving.

The detergent/dispersant package, which contains acid neutralization chemicals such as calcium or magnesium or borates, will attempt to neutralize the acids, but will probably be depleted quickly.

The tbn will most likely be going down for continued short trips.

As has already been suggested, UOA or more frequent oil changes might be in order, or at least draining a quart every 1.5 k and adding oil to replenish the additives might be a good idea.

[ December 09, 2002, 11:11 PM: Message edited by: MolaKule ]
1. When acids are neutralized, they go from acids to bases, which attack nothing. However, the basing additives become depleted over time, which is why I think it is a good idea to drop a quart and add a quart to replenish the basing additives. How soon do acids form? Depends on your fuel and oil additives, and varies from engine to engine.

3. The Aunt Minnie test showed that rust builds up in engines not driven often and with short trips. The SAE paper was written by Mobil chemists and engineers. Search on "Aunt Minnie."

4. Delvac 1 or Schaeffer's 700 would be a better choice of oil. Why. Better tbn and tbn retention (acid fighting) from detergent/dispersant package, better rust preventive packages, and better sludge control due to above factors.

Concentrate more on your oil (additive package)replenishment and less on when acids form and for how long.

As I stated before, at every 1.5 k drain a quart and add new oil to replenish the acid fighting capabilities of your oil and let the oil worry about it.

[ December 10, 2002, 01:30 PM: Message edited by: MolaKule ]
I drive a Saab, too (91 900S). WRT spark plugs - just a basic reminder - the best temp guide would be to look at the color of the plugs, after they've been run for a few K, and adjust plug temp up or down - if needed - from there. I.E., if they have the normal brown-to-grayish tan color, stay with them. If your using the popular NGKs, you may already be familiar with the "V" suffix - a gold palladium tip that are reportedly (I'm using the "S" s) better for your driving conditions. The V's cost 2-3 times as much as the S's, but last substantially longer. I wouldn't consider a plug temp change as a means of addressing the short run/acid problem/add pkg depletion problem, and running too hot a plug will cause you problems in other areas.

Some of 2.1Ls (91-93 MYs) have only one of the two cooling fans kick on, unless the AC is running, instead of both, as the car gets hot. I can send you more info but, in brief, when spring/summer/temps roll around, make sure both of you're fans are kicking on w/o the AC running (in case the problem spanned the 90 MY @ 2.0Ls) [there is a rewiring fix]

Again, the best recommendation here would be very frequent oil changes, using a diesel/gas rated oil. I certainly can't say it any better than MolaKule. I definitely understand economy, but your best value will come from protecting the engine well. You don't want those harmful by-products sitting in your crankcase for several months at a time.

Originally posted by MolaKule:
1. When acids are neutralized, they go from acids to bases, which attack nothing.


sorry for nitpicking

but when acids are neutralized, they form salts...
which don't attack most metals...
Eventually, yes they do turn into salts.

I thnk that in the interim, the base solution is weakened to a less base, and then if there are sufficient concentrations in solution, salts are formed as the final result.

I should also add, that the salts are only non-reactive if the salts do not decompose.

[ December 10, 2002, 08:32 PM: Message edited by: MolaKule ]
"1. When acids are neutralized, they go from acids to bases, which attack nothing."

And when the additive package is depleated and sulphuric acid continues to form in the oil corrosion continues and attacks internal parts,,

What salts are in the base after nuetralized ? The corrosive types?

[ December 10, 2002, 08:37 PM: Message edited by: dragboat ]

Good question.

First, I don't think acid build up is much of a problem unless you're running fuels or oils with high sulfur content (sulfuric acid); diesel fuels have higher sulfur content which is why a more robust detergent/dispersant package with high base (overbased, high TBN) are needed for diesels.

The only other acids that can form are from decomposition products of ZDDP and other additives that may contain phosphour and sulfur, and these would be weak acids at best.

When a base reacts with an acid, the acid is neautralized to form a salt and water. In other words, the reaction products of an acid and base produce, as a result, salt and water.

What oil formulators attempt to do is to make sure that there is more than enough basing chemicals to "soak-up" the acid and still retain a certain amount of base. When the tbn drops, this is an indication that the base is being consumed in fighting acids.

Edit: Think of the basing chemicals in the detergent/dispersant package as an acid "sponge." If you have a large sponge (overbased or robust basing package), the bases can soak up a lot more acid. If the basing chemical is weak (small sponge), the acids can build up in the oil.

Basing chemicals are generally calcium (or calcium carbonate), magnesium, and boron sulfonates or esters of such.

Tums and Pepto Bismol, for example, contain mostly calcium carbonates which react with the weak hydrochloric acid in the stomach (gastric acid) to relieve (neutralize) heartburn. The final product of these two chemicals is salt and water.

[ December 10, 2002, 09:51 PM: Message edited by: MolaKule ]
Addendum (which means I forgot something so here it is).

Nitric Acid:
Nitration of the oil resulting from combustion gas blowby, places nitrogen gases in solution in the oil. When these gases mix with water under heat, nitric acid forms. Nitric acid has been faulted for corroding cam lobes, followers, and other associated valve train components.

So the basing additives also have to maintain control of these acids as well.
Thanks for all the input & great links. Let me try to add some information relative to what's been discussed so far.

It's a 1990 Saab 900, 2.0L 4cyl, 160k miles, & I'm putting maybe 500 miles/mo on it right now. I put in Mobil 1 15W-50 on 02Oct, just before we got our first extended round of sub-freezing weather. I don't have an oil temp gauge. In warm weather the coolant gauge gets to normal within maybe five miles, but in cold weather it takes closer to ten. At the last major service (10k ago), the mechanics recommended a "super coolant" radiator additive due to the nature of these older Swedes running hot in the summer. (At the time I was putting about 1300 miles/mo on it.) The Owner's Manual lists only one spark plug for my non-turbo engine, but every mechanic I've talked to seems to prefer the next colder plug for this car. None of them have any real convincing reasons as to why. (The Manual lists a colder plug for the turbo version of this engine in city driving, & the next colder plug (2 steps below mine) for the turbo in hwy driving.) I do try to take longer drives when I can. Some mornings I'll return home to get my bike, & some evenings I drive in the opposite direction to get between 6-10 miles in. I use the car most weekends for errands, but that could be anywhere between 10-50 miles.

How quickly do these acids form? Seconds? Minutes? Longer?
If moisture is combining with other stuff to form acids, & the additive pkg is neutralizing the acids, what happens to the moisture?
If I drive for 40-50 miles, does that drive out only the moisture & leave the other stuff behind?
Once the moisture/acid is driven off, does that "free up" the additives to neutralize more acid?
Is there some link to the oft-referenced "Aunt Millie" test?

I guess I thought the slightly hotter plug recommended in the manual would warm up the cylinders a bit faster than the colder plug recommended by the mechanics, leading to less accumulated moisture. I'm not going to run interim UOA on this vehicle (due to cost & inconvenience), but I plan to run one after maybe a year, & definitely at 10k. I don't want to change it frequently (even partially), which is why I'm using M1, but I'll probably do a filter change at one year. And the car does still seem to be using/losing some oil, so I'll be adding a few ounces every 3-4 mos. I like the idea of using something like Delvac 1 for these conditions, so maybe I'll top up with that instead of more 15W-50. I guess the only real concerns I have are with dragboat's comments about the acids neither burning off or evaporating.

Thanks again for all the help.
Kule, Thanks for the reply but feel the nead to post this:
"What oil formulators attempt to do is to make sure that there is more than enough basing chemicals to "soak-up" the acid and still retain a certain amount of base. When the tbn drops, this is an indication that the base is being consumed in fighting acids."

Is this why on the back of a quart of Pennzoil Group III with Pennzane it clearly states to change oil every 3 months or 3k miles for something to the tune of best protection. Are they implying that oil might not go the distance?

[ December 11, 2002, 10:35 AM: Message edited by: dragboat ]
They are indeed implying the oil might not go the distance, since the additive package probably "peters-out" by this time.
And this is where the chemists, the engine engineers, and the materials scientists have to work together, i.e., Not too sour, not too sweet.

[ December 11, 2002, 01:55 PM: Message edited by: MolaKule ]
And/or they want you to change your oil more frequently so they can sell more oil, or they want to give the consumer a "pat on the head" by confirming something he already believes.


[ December 11, 2002, 12:52 PM: Message edited by: Ken2 ]
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