When Oil Cracks

NZ Truth, Issue 1080, 12 August 1926, Page 16

When Oil Cracks

', An oil 'which will cause, rapid car.-jj bonization is a mixture of light, anc}' heavy fractions blended' to obtain .'.ia, suitable viscidity. „: „ . ;f It is obvious that m this class 'tHe lighter constitutent will be volatilised and burnt at a. lower temperature .than the heavier oil with wliich it is nijxed with the l-esuit that a-residue : of this viscuous lubricant will remain in| t)ie combustion chamber until prolonged exposure to heat causes "cracking" pf the oil, with the formation- of ajcoiisiderable quantity of carbon- > Fatty oila such ns ' castor, rape and t lard are frequently; incorpora^ted in.small percentages with thbse" of mineral origin and enormously, 'improve the lubricating value. v : f Contrary to the opinion of many . motorists, these! fatty pi lsj ( -if pres- . ent m small .proportions vonly, dp' not affect; the rate of carbon formation; it, is not advisable, how- : ever, to use lubricants I high percentages ,of these oils m. engines other . than <i 'tho.se designed for high speed, and ■> then only \ with the approval of the manufacturers. ,