Oils & lu­bri­cants

Motor Equipment News - - CONTENTS -

New Zealand has a grow­ing num­ber of oil com­pa­nies, both in­de­pen­dent and part of global conglomerates, and all of them are com­pet­ing for your busi­ness, or more to the point, the busi­ness of your work­shop cus­tomers.

So first up, how do you de­cide what’s the best oil to use? Do you just look at the rat­ings given in the hand­book or on a chart, or do you look at other fac­tors, such as av­er­age out­side tem­per­a­tures, or the way the ve­hi­cle is going to be used?

The In­sti­tute of Ma­te­ri­als (IOM) is an in­de­pen­dent or­gan­i­sa­tion that con­ducts re­search on oil sam­ples from around the world, and then pro­vides the re­sults to mo­tor man­u­fac­tur­ers, oil com­pa­nies, and fleet man­agers.

IOM has also set down ba­sic terms which make it eas­ier to un­der­stand the na­ture of en­gine lu­bri­cat­ing oil, and how they es­tab­lish each clas­si­fi­ca­tion.

The first term, and one we are prob­a­bly all the most fa­mil­iar with, is vis­cos­ity. This is the most im­por­tant con­sid­er­a­tion when choos­ing an oil, since it’s what de­cides how fast an oil flows. The vis­cos­ity of an oil must be thick enough to lubri­cate and pro­tect, but thin enough to flow through oil gal­leries and spread evenly over all bear­ing sur­faces at low tem­per­a­tures.

Next up is the oil grade. This is as­so­ci­ated with vis­cos­ity in that it’s a mea­sure­ment estab­lished by the As­so­ci­a­tion of Au­to­mo­tive Engi­neers (SAE) to in­di­cate how fast an oil flows. The higher the SAE num­ber, the thicker the oil – and thick oils flow slower than thin oils.

How­ever, oil tem­per­a­ture in an en­gine varies. At low tem­per­a­tures, es­pe­cially when first start­ing up, you need a thin oil that flows bet­ter when the en­gine is cold. But once the en­gine is run­ning you want a thicker oil that gives bet­ter pro­tec­tion to the bear­ings.

For this rea­son multi-grade oils were de­vel­oped, and they have two SAE grades, in­di­cat­ing low and high tem­per­a­ture char­ac­ter­is­tics.

For in­stance a typ­i­cal SAE 10W30 oil (W stands for win­ter) in­di­cates good flow char­ac­ter­is­tics when the en­gine is cold, while the sec­ond num­ber refers to the oil film strength – its lu­bri­cat­ing power – at 100 deg. C.

In colder ar­eas, such as in the bot­tom of the South Is­land, for in­stance, it might be prefer­able to use an oil with a lower start­ing tem­per­a­ture, such as a 5W20, whereas Auck­land weather wouldn’t re­quire such a low ini­tial “start” num­ber.

And now here’s where it starts to get a bit com­pli­cated. Orig­i­nally all oils were min­eral oils, pumped out of the ground from pe­tro­leum de­posits, and these oils vary in qual­ity, in the amount of sul­phur they con­tain, and how cleanly they burn in the en­gine – as hap­pens in the com­bus­tion cham­ber – and in the amount of car­bon de­posits they leave be­hind on in­ter­nal en­gine parts.

Then, led by the ex­tra load on oils found in mo­tor sport, air­craft en­gines, and space ex­plo­ration, new oils were needed that would con­tinue to pro­tect the en­gine in ex­treme con­di­tions. So syn­thetic oils were de­vel­oped, with re­sis­tance to high tem­per­a­ture break­down and de­posit for­ma­tion, cou­pled with ad­di­tives to im­prove their lu­bri­cat­ing power.

Many mod­ern en­gines are de­signed to only use syn­thetic oils, es­pe­cially to­day’s small turbo units with their tight tol­er­ances and higher com­bus­tion tem­per­a­tures.

Sim­i­larly, diesel en­gines, which have higher in­ter­nal op­er­at­ing tem­per­a­tures than petrol en­gines, re­quire their own oils.

Syn­thetic oils are gen­er­ally more ex­pen­sive than or­di­nary min­eral oil, but a new class of oils has been de­vel­oped which com­bines both to give bet­ter pro­tec­tion than pure min­eral oil, but at lower cost than pure syn­thet­ics.

Fi­nally, there’s ser­vice clas­si­fi­ca­tion, which is set by the Amer­i­can Pe­tro­leum In­sti­tute, and com­prises letters which ap­pear in the dough­nut-shaped ring on oil con­tain­ers.

The sys­tem rates an oil’s abil­ity to control wear, sludge, var­nish, thick­en­ing, rust, cor­ro­sion, and pis­ton de­posits.

The API ser­vice classes have two gen­eral clas­si­fi­ca­tions: S for “ser­vice/spark ig­ni­tion” (typ­i­cal pas­sen­ger cars and light trucks us­ing petrol en­gines), and C for “com­mer­cial/com­pres­sion ig­ni­tion” (typ­i­cal diesel equip­ment). En­gine oil which has been tested and meets the API stan­dards may dis­play the API Ser­vice Sym­bol (also known as the “Donut”) with the ser­vice des­ig­na­tion on con­tain­ers sold to oil users.

The lat­est API ser­vice stan­dard des­ig­na­tion is SN for petrol car and light-truck en­gines. The SN stan­dard refers to a group of lab­o­ra­tory and en­gine tests, in­clud­ing the lat­est se­ries for control of high-tem­per­a­ture de­posits. Cur­rent API ser­vice cat­e­gories in­clude SN, SM, SL and SJ for petrol en­gines. All pre­vi­ous ser­vice des­ig­na­tions are ob­so­lete, although mo­tor­cy­cle oils com­monly still use the SF/SG stan­dard.

There are three diesel en­gine ser­vice des­ig­na­tions which are cur­rent: CJ-4, CI-4, and CH-4. Some man­u­fac­tur­ers con­tinue to use ob­so­lete des­ig­na­tions such as CC for small or sta­tion­ary diesel en­gines. In ad­di­tion, API cre­ated a sep­a­rated CI-4 PLUS des­ig­na­tion in con­junc­tion with CJ-4 and CI-4 for oils that meet cer­tain ex­tra re­quire­ments, and this mark­ing is lo­cated in the lower por­tion of the API Ser­vice Sym­bol “Donut”.

It is pos­si­ble for an oil to con­form to both the petrol and diesel stan­dards. In fact, it is the norm for all diesel rated en­gine oils to carry the “cor­re­spond­ing” petrol spec­i­fi­ca­tion. For ex­am­ple, API CJ-4 will al­most al­ways list either SL or SM, API CI-4 with SL, API CH-4 with SJ, and so on.

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