In oil analysis, what does % oxidation & % nitration mean?

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Aug 13, 2002
I found the definition for oxidation:

'Oxidation measures gums, varnishes and oxidation products. High oxidation from oil used too hot or too long can leave sludge and varnish deposits and thicken the oil. '

What about the definition for nitration?

What is the acceptable % range for oxidation & nitration?
Here is something I saved in one of my emails. I believe it was from MoleKule, but it could've been written by Bob or Terry as well.


Nitration results from the heating of O, O2, N2, OH, and H in the
cylinder during combustion. The separate gasses mix
and when burned, form many resulting gasses
including NOx.

NOx generation is highest during: high
pressures, high temperatures, during crank angles between 10 and 40
degrees, and when the A/F ratio gets near
16:1, such as in lean-burn engines.

NOx gets into the oil via the blow-by gasses
during the power cycle when the cylinder pressure is highest and when
when the temp of the buring gasses is highest.

EGR valves and large overlap cams introduce
exhaust gas back into the cylinder to cool it down, reducing generation

NOx creates peroxides that attack the oil and
increase oxidation as well..

From that same email:


1. Oxidation - oxygen interrupts or attacks
the hydrocarbon bonds and breaks them up at high temperatures, turning
the molecules into sludge, varnish and
lacquer. Synths have stronger molecular bonds and better molecular
arrangements than do dinos, since synths were
engineered to do that. Hence the better oxidation resistance, wider
VII, and greater film strength.


Originally posted by Ken4:
What causes the oil to go black? Is it the oxidation and nitration?

I don't believe so. My wife's last oil change showed her oil still a nice honey color on the dipstick after 5k and it had 17% ox and 34% nit.

Also, a lot of cars turn the oil black almost right away (diesels do for sure). I believe the darkness of an oil is more from the contaminents in it (in the case of diesels I believe it's soot which turns it black so fast)
In the short term, it's unburned hydrocarbons and ultrafine particles of grit and metal that turns an oil dark.

In the long term, oil can turn dark due to oil and VII molecules shearing, and the burning of some additives. Oxidation can cause the acceleration of molecular destruction and add to the opacity of the oil.
In oil analysis, what is the normal % range for oxidation & nitration? e.g. what is considered 'excellent', 'good', 'satisfactory', 'poor', etc.
Excellent would be under 10%, good would be 10-20, satisfactory would be 20-50 and 50 or higher would be poor. This is my opinion anyways, and based on a 5-6k interval.
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