oil analysis involves sampling and analyzing oil for various properties and materials to monitor wear and contamination in an engine , transmission , or hydraulic system . sampling and analyzing on a regular basis establish a baseline of normal wear and can help indicate when abnormal wear or contamination is occurring . oil analysis not only provides a window into the mechanical condition of the component , but also determines the condition of the oil itself to help optimize drain periods [ 24 ] . the first use of used oil analysis dates back to the early 1940s by the railway companies in the western united states . prompted by the purchase of a fleet of new locomotives , technicians used simple spectrographic equipment and physical tests to monitor locomotive engines [ 5 , 6 ] . as steam locomotives gave yield to diesel locomotives , oil analysis practices by railways were caught on . by the 1980s , oil analysis formed the basis of condition - based maintenance in most railways in north america . owing to the success of oil analysis in the railways , the american navy used spectrometric techniques to monitor jet engines on their aircraft in the mid 1950s . around this time oil analysis began to spread and programs were developed by the american army and air force throughout the 1950s and early 1960s . then commercial oil analysis laboratories first appeared on the scene in the early 1960s [ 5 , 6 ] .   at present oil analysis regards an important part of condition monitoring in advanced industrial countries . by employment of such programs , considerable saving in time and costs has been obtained [ 7 , 8 ] . beside technical reports , a number of papers with the subject of oil analysis can be found in literature [ 916 ] . in diverse papers the application of a wide range of analytical procedures and methods such as potentiometry , polarography , inductively coupled plasma , fourier transformation infrared spectroscopy [ 18 , 19 ] , atomic absorption spectroscopy , differential scanning gravimetry , x - ray fluorescence spectroscopy , laser - induced break down spectroscopy , spectrography , ferrography , mass spectrometry , and chromatography   have been described .   in an oil analysis , the concentration of a number of elements as well as the quantity of some of the physical properties such as viscosity , viscosity index , density , flash point , pour point , total acid and base numbers , and water content [ 28 , 29 ] is determined . the resulting data are then employed for the diagnosis of the conditions of oil and motor . oil analysis can detect , fuel dilution of lubrication oil , dirt contamination in the oil , antifreeze in the oil , excessive bearing wear , and misapplication of lubricants . early detection can reduce repair bills , diminish catastrophic failures , increase machinery life , and lessen nonscheduled downtime . we have recently been involved in the investigation of lubrication oils [ 3032 ] . in this paper , we report the results of the physical and chemical monitoring of a mineral - based gasoline lubricant at different operation kilometers . the selected oil is a product from sepahan oil company . base oil sn-500 and gasoline oil speedy sl from sepahan oil company were used directly . methanol , hydrochloric acid , perchloric acid , different buffers , propane-2-ol , chloroform , potassium hydroxide , acetic acid , acetic anhydride , chlorobenzene , sodium perchlorate , xylene , acetone , and solid carbon dioxide were purchased from merck company and used without any processing . the test methods were followed as : astm d-445 for viscosity at 40c and 100c , astm d-2270 for viscosity index , astm d-92 for flash point , astm d-97 for pour point , astm d-1298 for specific gravity , astm d-1500 for color , astm d-664 for total acid number , and astm d-6304 for water content . all of the viscosities , viscosity indices and specific gravities were determined by viscometer anton paar model svm 3000 . ftir spectrum was recorded on a ftir spectrum perkin elmer model spectrum 65 using kbr pellet . the elemental analysis of the base oil , that is , sn-500 and formulated oil ( speedy sl ) was performed by icp - oes perkin elmer model optima 5300  v. the detection limits ( dls ) were obtained under simultaneous multielement conditions with the axial of a dual - view plasma using a cylonic spray chamber and a concentric nebulizer . all detection limits are given in microgram per liter and were determined using organometallic standards . the selected wavelengths and the values of dl ( values in parentheses ) for each element are as shown in table 4 .   at each running kilometer the concentrations of twenty - four element in lubrication oil and at different kilometers have been determined by icp - oes . the corresponding values are given in table 1 . also , the standard deviations due to each of the data are given in table 2 . the results have been sorted based on the decreasing trend in fresh oil . at first glance , the obtained data can be divided to three groups , ( i ) elements that their concentrations are more than 10  ppm , ( ii ) elements with concentration less than 10  ppm but more than ld , and ( iii ) elements , which do have below ld concentration . according to this categorization sulfur , zinc , phosphorous , magnesium , silicon , calcium , and barium can be located in the first group , boron , molybdenum , aluminum , silver , chromium , nickel , and sodium are the members of the second group and the rest of elements , that are , manganese , iron , copper , tin , titanium , vanadium , lead , cadmium , antimony , and potassium belong to third group . on the other hand , the obtained data indicate that upon the continuous usage of the oil and at higher kilometers , the concentration of some of the elements decreases continuously , mean while an increasing trend is observed for other elements . one of the sources of the elements in fresh oil is additives , that are , the compounds which are employed in the oil formulation and do have the role of enhancement of the physicochemical properties of the oils . depending on the application , various combinations of additives are used to meet the required performance level ; the most important are detergents , dispersants , antiwear , antioxidants , viscosity modifiers , foam inhibitors , and pour point depressants [ 35 , 36 ] . thus , zinc dialkyldithiophosphates ( zddps ) are common antiwear and antioxidant , which contain zn , p , and s in their structure , calcium and barium salts of long chain alkylarylsulfonic acids are common ca - containing detergents , and liquid silicones are the most efficient antifoam agents , which include si in their structure . the other source of the elements in the fresh lubricant oil are those elements , which in the process of base oil production are incorporated . because of the organic character of the base oil , it is anticipated that its metallic elements are less than the nonmetallic ones . 114 in fresh oil originate from two sources of base oil and additives . in the case of metallic elements it is anticipated that the base oil has minor contribution and the main part is due to additives . in other cases such as sulfur and phosphorus , the contribution of both sources may be considerable .   in order to have a better understanding of the sources of the elements in the fresh oil , the obtained results are given in the second column of table 1 ( values in parenthesis ) . as it can be seen , except s , the concentration of other elements is less than 10  ppm . considering that the employed base oil , belongs to group ( i ) , such a high level of s is not abnormal . on the other hand , because of organic character of the base oil the low concentration of metallic elements is not unexpected .   as the data shown in the fresh oil s does have the most concentration . this can be attributed to ( i ) high level of s in the base oil and ( ii ) application of zddp , which is a sulfur - containing additive and normally is employed in crankcase oil formulations . zinc and phosphorous are the second and third highest concentration elements ( table 1 ) . the comparison of the level of these elements in fresh oil with those of base oil indicates huge increase in the later relative to the former . such an observation can also be assigned to the usage of zddp ( as a zn and p containing additive ) in the oil formulation . the elevated levels of mg , si , ca , and ba can be related to the application of additives such as basic phenates or magnesium sulfonate , silicon antifoam , calcium sulfonate , and barium sulfonate . 714 in the base oil with those of fresh oil ( table 1 ) does not show any significant change . this means that in the lubricant formulation , additives which contain the recent elements have not been employed . the concentrations of elements no . 1 to 7 , which are incorporated in additive structures , versus the running kilometer are given in table 1 . as it can be seen , in all cases upon the oil usage , the concentrations are reduced continuously . in fact , at high engine temperature , the additives are degraded and some of the resulting degradation products are absorbed by the filter . which result in lowering of the concentrations of the corresponding elements in the oil . it is interesting to note that the amount of reduction is more sever for zinc and phosphorus , which indicate that depletion of corresponding additives are more than the other ones . wear metals will appear in the oil because of wearing of different parts of engine , fe is the most common of the wear metals . present in some form in virtually all equipment . . it can be found in cylinder liners , piston rings , valve train , crankshaft , rocker arms , spring gears , lock washers , nuts , pins , connecting rods , engine blocks , and oil pump . cu is widely used as an alloying element , copper is prized because of its materials properties , very ductile and excellent thermal and electrical conductivity . it is heavily used in bearing systems , as well as heat exchangers . in the engine , it can be found in valve train bushing , wrist pin bushing , cam bushings , oil cooler core , thrust washers , governor , connecting rods bearings , and valve gear train thrust buttons . tin is used as an alloying element with copper and lead for sacrificial bearing liners . in the engine , it can be found in valve train bushing , wrist pin bushing , cam bushings , oil cooler core , thrust washers , governor , connecting rods bearings , and valve gear train thrust buttons . aluminum is valued in equipment because of it high strength to weight ratio and excellent corrosion resistance . , it can be found in engine blocks , pistons , blowers , oil pump bushings , bearings ( some ) , cam bushings ( some ) , and oil coolers ( some ) . it can be found in rings , liners , exhaust valves , and zinc chromate from cooling system inhibitor . lead is used in a soft metal used for sacrificial wear surfaces such as journal bearings . silver has exceptional thermal conductivity and is an excellent bearing plate material , providing minimum friction . , it can be found in valves , valve guides , cylinder liners , and bearings . the data in table 1 indicate that , upon increase of running kilometer , the concentration of wear elements has been increased continuously . this means that during the performance , some wear has been occurred in different parts of the engine . among the elements as it can be seen , the concentration of iron has been changed 12 units and the concentration of manganese has been changed 15.5 units . meanwhile , the decreasing trend of boron concentration may be due to the formation of boron compounds in oil matrix , which are absorb in oil filters . the concentrations of the elements , which are neither due to base oil , nor due to additive , are given in table 1 . as it can be seen , the concentrations of wear elements that are , manganese , iron , copper , tin , titanium , vanadium , lead , cadmium , and antimony have been increased . meanwhile , the concentration of potassium , which is a contaminant element   show a sudden increase in 11500  km . this may be due to initiation of some leakage of coolant to the oil . consistency , flow properties , or viscosity in the case of oils are key parameters to create lubrication efficiency and the application of lubricants . the viscosity of used engine oil can drop for reasons of fuel dilution or because of high water content and/or shearing of the vi improver . viscosity can increase because of heavy contamination of the oil by soot , polymerization , vaporization losses , and emulsions due to water contamination and/or oxidation of the oil . obviously , the final status of the oil viscosity depends on the combination effects of decreasing and increasing factors . if the falling factors are overcome to the rising ones , the drop in viscosity will happen . an increase in the property will be observed , in the reverse conditions .   as it can be seen from the table 3 until 2000  km running , the viscosity at 40c and 100c decreases systematically . this indicates that before 2000  km , the viscosity decreasing factors such as fuel dilution , water contamination , and shearing of the vi improver conquer to increasing ones . meanwhile , at running kilometers more than 2000 , the increasing factors such as heavy contamination of the oil by soot , polymerization , vaporization losses , and emulsions due to water contamination and/or oxidation of the oil are overcome to decreasing agents . since there is no signal of fuel dilution , decreasing of viscosity can mainly attributed to water contamination and shearing of the vi improver . on the other hand , absence of 2000  cm band in ir spectrum of used oil ( figure 1 ) which is an important sign of soot formation [ 18 , 19 ] , as well as , lack of satisfactory reasons for vaporization losses and formation of emulsion , verify that polymerization and oxidation are the major motivation of viscosity increase .   the observed bands in the ir spectrum of used oil ( figure 1 ) can be assigned to ch stretching ( 2924  cm ) , carbonyl ( 1714  cm ) , ch2 scissoring ( 1460  cm ) , symmetric bending of ch3 ( 1376  cm ) , and aromatic compounds ( 970  cm ) . the observation of recent bands can be attributed to the existence of aromatic , naphthenic , and aliphatic compounds , which are constituents of employed mineral base oil ( sn-500 ) . in addition , the observation of carbonyl band indicates that some oxidation has been occurred . the low intensity of the observed peak means that the degree of oxidation is low . the flash point is the lowest temperature at which an ignition source causes the vapors of the specimen ( lubricant ) to ignite under specified conditions . like viscosity , the flash point test has always been a standard part of a lubricant 's specification . because of the low - flash points of most fuels , a sudden drop in flash temperature in crankcase oil , localized temperatures can lead to thermal cracking within the oil . as no variation of flash point the fixation of pour point , which is the normal result of thermal cracking , is a further confirmation of the absence of thermal cracking . if both of increasing and decreasing factors exist simultaneously , the final situation will be determined by the preference factor . observation of increasing trend ( table 1 ) , beside the absence of fuel dilution or contamination indicates that oxidation is the main reason of the raise in specific gravity .   the total acid number is a measure of the acidic constituents in petroleum products . the acidity of unused oils and fluids is normally derived from the type and concentration of specific additive material , whereas the acidity of used oil is of interest to measure the degree of oxidation of the fluid . the total base number ( tbn ) it is particularly used for engine oils , where by acidic combustion products use up the alkaline reserve . the plots of tan and tbn versus kilometers of operation are shown in figure 2 as it can be seen upon increasing the running kilometer , the tan increases continuously . the rising trend of tan can be attributed to oxidation of some of the lubricant constituents and subsequent formation of carboxylic acids . in fact , upon increasing the operation time of the oil , the antioxidant additives will deplete gradually . the depletion of antioxidants beside the high temperature of engine and presence of oxygen provides suitable circumstances for oxidation . the appearance of carbonyl band in ir spectrum of used oil ( figure 1 ) is a further evidence of oxidation . in contrast , to tan a lessening drift is observed for tbn ( figure 2 ) . this decreasing trend can be assigned to depletion of additives , which mostly do have basic character . this is in accordance with the results of elemental analysis ( table 1 ) which fairly confirms the depletion of additives .   considering that , tbn is a measure of alkaline reservation of lubricant . it is expected that after complete consumption of alkaline materials the neutralization to be stopped completely and sudden elevation of tan to be observed . obviously , after this point , the destructive effects of acidic products will be very high and further usage of the oil is not wisdom . upon extrapolation of tbn and tan curves , it can be predicted that approximately at 23000  km these two recent values will be equal . therefore , it can be concluded that 23000  km is a critical value and the time of oil replacing . water can be present in three forms of dissolved , emulsified , and free in lubricating oils . the concentration of dissolved water is less than 100  ppm and is not harmful nor does it affect the appearance or performance of the lubricant . emulsified water exists in more than 150  ppm and causes milky appearance of the oil . this form of water in oil is also very harmful to lubricated parts but is also the easiest to separate . as it can be seen from the table 3 , despite increasing trend of water content , its concentration has not reached to critical value . consequently , in present oil , water can not be regarded as an important harmful factor and its contribution in damages is negligible . based on the observed results it can be concluded that through different operation kilometers the following changes are happened : the additives depletion ; increase and decrease in rheological properties ; increase of tan and decrease of tbn due to oxidation ; a few water contaminations ; not many coolant leakage .
physicochemical properties of a mineral - based gasoline engine oil have been monitored at 0 , 500 , 1000 , 2000 , 3500 , 6000 , 8500 , and 11500  kilometer of operation . 
 tracing has been performed by inductively coupled plasma and some other techniques . at each series of measurements , 
 the concentrations of twenty four elements as well as physical properties such as : viscosity at 40 and 100c ; viscosity index ; flash point ; pour point ; specific gravity ; color ; total acid and base numbers ; water content have been determined . 
 the results are indicative of the decreasing trend in concentration of additive elements and increasing in concentration for wear elements . 
 different trends have been observed for various physical properties . 
 the possible reasons for variations in physical and chemical properties have been discussed .