why limits and why changing oil

Dear motorist,

I have a question for you: Why there are limits and alarms in medicine? Why pay attention to limits and alarms when it comes to cholesterol, or blood pressure, or counts of white and red blood cells, or vitamins' deficiencies, etc., and why we bother to take medications based on these limits and alarms? Or shouldn’t we be concerned only with a speed of variations? The same could be said for lube oils, because they are considered the blood of equipment. I tend to pay attention to limits and alarms and react accordingly (and I would suggest you do the same). For example, when viscosity or acid number reach alarm limits, I wouldn’t resort to medication (additives) to restore oils health; I would change it, instead. However, in cases when moisture and particle count are reaching high limits, I would use medications (demoisturizing and filtration) to bring back health to my lube.

Nevertheless, the rate of change is important, but not to directly access service life of oil, and to make decision of changing it or not. Instead, I would use such data to assess the system’s (equipment) reliability.

than you John,

I absolutely agree with you if we speek about the oil condition.An oil have to assure some functions and if it lose its propertie therefor we must have limts.

But my qustion is about wear particles, so if my lubricant is in good condition and the wear is linear I mean there is no abnormal wear, am I obliged to change the lubricant if the level of lead reach 30 ppm (30ppm is a limit for engine lubricant).

thanks and excuse my bad english.

I don't think you need to change your oil due to the particular lead conc, but obviously, something is not right, and you should be investigating where this lead is coming from.

In line with this, I'd like to know if there's any alarm limits for depletion of additives in oil (from elemental spectroscopy). How would we consider the oil is not fit for use, assuming all other properties (e.g. viscosity, acid number etc) in normal condition. Obviously high wear metal concentration would be cause for concern, but what about decrease in additives level?