1. Cooling and Lubrication Systems Chapter 8

2. Cooling Systems

3. Introduction
Internal combustion engines use heat to convert the energy of fuel to power.
Not all of the fuel energy is converted to power.
Excess heat must be removed from the engine.
In engines, heat is moved to the atmosphere by fluids--water and air.
If excess heat is not removed, engine components fail due to excessive temperature.
Engine temperature is not consistent throughout the cycle.
Heat moves from areas of high temperature to areas of low temperature.

4. Engine Construction
Engine components are constructed of aluminum and cast iron alloys, steel and non-metallic materials.
The physical properties of these alloys determines the physical characteristics of the engine components.
Desirable cast iron properties.
Greater density
Structural integrity when mechanically or thermally stressed.
Porous surface--improved lubrication.
Graphite enhanced lubrication.
Less dimensional changes when heated.
Undesirable properties of cast iron:
Increased weight
Propensity for oxidation/corrosion
Difficulty machining
Relative poor heat conductivity.

5. Engine Construction-cont.
Desirable properties of cast aluminum:
High strength to weight ratio.
Lower production cost
Excellent heat dissipation
Undesirable properties of cast aluminum:
Higher raw material costs
Less resistant to wear.
Greater thermal expansion
Aluminum is the material of choice for modern small gas engines.

6. Cooling Terms Thermal Conductivity Thermal expansion
Ability of a material to conduct and transfer heat
Thermal expansion
Expansion of a material when it is heated.
Thermal growth
Increase in size caused by heating.
When cooled does not return to normal size.
Thermal distortion
Asymmetrical or nonlinear thermal expansion.
Three means of heat transfer:
Conduction
Convection
Radiation

7. Heat Movement Conduction Convection Radiation
Movement of heat through materials.
Convection
Movement of heat by fluids.
Radiation
Heat movement by transfer from one body to another.

8. Two Cooling Systems Small engines use two cooling systems;
Air
Liquid
Both systems have two common features.
Heat is transferred from the combustion chamber to the crankcase by the oil.
A large portion of the excess heat is removed with the exhaust gases.
The difference is in the medium used to move the heat from the engine to the atmosphere.

9. Air Cooled Heat Movement
In air cooled engines the excess heat in the combustion chamber moves through the cylinder walls by conduction.
The heat transfers from the engine parts to the air at the exterior surfaces and into the atmosphere by convection.
The air fins increase the surface area between the engine and the air--increasing heat transfer.
The heart of the system is the fins on the flywheel which pumps the air around the engine.
The air flow is directed by the air shrouds.

10. Water Cooled Heat Movement
Water cooled engines transfer the excess heat from the combustion chamber through the cylinder walls by conduction.
Water flowing past the exterior cylinder walls absorbs the heat and transfers it to the radiator.
Air flowing through the radiator absorbs the heat and transfers it to the atmosphere.
The system relies on a water pump to circulate the water through the system and a fan to move air through the radiator.

11. Lubrication System

12. Introduction
The lubrication system provides oil to appropriate areas of the engine to maintain a film of oil to separate bearing surfaces.
Oil also transfers combustion heat to the crankcase.
An important characteristic of oil is the viscosity.
Viscosity is the internal resistance to flow of a fluid.
The SAE rates the viscosity of oils.
Low viscosity means a high volume of oil flows through a specific orifice at a specified temperature, atmospheric pressure, and time period.
Multi-viscosity oils are popular because they offer low viscosity characteristics in low temperatures and high viscosity characteristics with higher temperatures.

13. Oil Standards Service Categories--Gasoline Engines
SA, SB, SC, SD, SE, SF, SG, SH are obsolete.
SJ: 2001 and older automotive engines.
SL: All automotive engines manufactured after July 2001.
Service Categories--Diesel Engines
CA, CB, CD, CE are obsolete.
CF: Off road, indirect-injected manufactured after 1994 and with fuels over 0.5% sulfur.
CF-2: Severe duty, two cycle engines.
CF-4: High speed, four cycle engines.
CG-4: Severe duty, high speed, four stroke, with fuels less than 0.5% sulfur.
CH-4: High speed, four stroke engines designed to meet 1998 exhaust standards.
CI-4: High speed, four stroke engines designed to meet 2002 exhaust standards.

14. Lubrication Systems
Small engines use one of three lubrication systems.
Splash
Pressure filtration
Pressure