Popular Science Montlih/ 



265 



TEMP OF CYLINDER 

 WALLS l90-350°-F. 



/HEAT OF EXPLOSION 

 ,/ 2000''-30OO°-F. 



^^,^TEMP. or PISTON- 

 HEAD 300°-I000-F 



tpiSTON SURFACES 

 2OO°-4O0°-F 



iiCRANKBEARINGQIL 

 TEMP. 140°- 250F 



TEMP. OF SUMP OIL lOO - 150 F. 



In many cars the Splash Lubricating System is employed. Oil is supplied to the crankcase. 

 The connecting rods dip into and splash the oil to all other parts of the engine. The tem- 

 peratures of the various parts are indicated in the diagram and show the heat to which 

 the lubricating oil is subjected. The parts that are lubricated are indicated in white 



water and has a curdled appearance; but 

 good oil shows a clean line between the 

 oil and the water. The test indicates 

 whether or not the refiner has removed 

 harmful acid compounds and other im- 

 purities. 



Of all these tests those which indicate 

 an oil's viscosity and heat-resisting 

 qualities are the most significant, be- 

 cause they show whether or not an oil is 

 able to form and maintain the film that 

 separates the friction surfaces and i)rc- 

 vents the escape of gases past the piston 

 during the compression and power 

 strokes. 



The accompanying pictures .show what 

 happens when poor, clieai) oil is used 

 in a motor car — an oil which fails to 

 meet the tests mentioned. If the oil 

 has insufficient body ami cannot stand 



heat, metal rubs on metal ; piston rings . 

 break; the cylinder walls arc scratched 

 anil scored. 



.'\n oil of low \iscosity is easily sucked 

 past the piston rings into the explosion 

 chamber. That means compression losses, 

 because of the poor gas seal formed by 

 the oil. What is more, the carbon of the 

 oil — the carbon which is an indispensable 

 chemical constituent of every oil — is 

 deposited in a more or less thick coat. 

 Subjected to the heat of thousands of 

 exjilosions in a few minutes, this carbon 

 acts like so much coal. Parts of it be- 

 come incandescent. Hence, mixtures are 

 prematurely exploded. "Knocking" of 

 the motor results, which means that the 

 glowing carbon ignites the mixture before 

 the piston has reached the top dead 

 center, thus giving rise to powerful blows 



