ENGINE OIL TESTS
LOW TEMPERATURE OPERABILITY STARTABILITY & CHARACTERISTICS The ability of an engine oil to flow or be pumped at low temperatures especially at start up is critical to the life of an engine. Failure of the engine oil to flow or be pumped to critical areas of the engine at start up can result in catastrophic engine failure. Two ASTM tests used to measure an engine oils low temperature operability are: - Cold Cranking Simulator ASTM D-5293D - Mini Rotary Viscosity TP-1 1 Engine Oil Pumpability Test ASTM D-4684D
COLD CRANKING SIMULATOR ASTM D-5293D The Cold Cranking Simulator Viscosity Test Method is used to measure an engine oil s s ability to permit a satisfactory cranking speed to be developed in a cold engine at startup. The viscosity of the engine oil in engine journal bearings during cold temperature startup is a key to determining the lowest temperature at which an engine will start. The Cold Cranking Simulator viscosity is determined under conditions similar to those experienced in engine bearings during startup. The SAE has established maximum limits for each multi-grade engine oil.
COLD CRANKING SIMULATOR ASTM D-5293 D LIMITS SAE GRADE COLD CRANKING VISCOSITY @ TEMPERATURE C 0W-XX 5W-XX 6200 @ -35 C 6600 @ -30 C 10W-XX 7000 @ -25 C 15W-XX 20W-XX 7000 @ -20 C 9500 @ -15 C
MRV TP-1 1 ASTM D-4684D This test method is used to measure an engine oil s ability to flow to the engine oil pump and provide adequate oil pressure during the initial stages of low temperature operation. At low temperatures an engine oil can gel to a semi- solid state or be so high in viscosity that it fails to flow to the oil inlet pump when the engine is started after standing at low temperatures If the oil pump pumps air instead of engine oil both the oil pump and other engine parts can be damaged due to lack of lubrication.
MRV TP-1 1 ASTM D-4684D The MRV TP-1 1 Viscosity is determined under low temperature cooling conditions similar to those experienced by an engine during actual field conditions. The SAE has established maximum limits for each multi-grade engine oil.
MRV TP-1 1 ASTM D-4684 D SAE GRADE LIMITS SAE GRADE PUMPING VISCOSITY, Cp with no Yield Stress 0W 5W 10W 15W 20W 60,000 @ -40 C 60,000 @ -35 C 60,000 @ -30 C 60,000 @ -25 C 60,000 @ -20 C
HIGH TEMPERATURE HIGH SHEAR VISCOSITY ASTM D-4683D The High Temperature High Shear Viscosity Test is used to measure an engine oil s s ability to provide an effective adequate viscosity in high shear components such as the journal bearings and between the piston rings and cylinders under severe operating conditions. The values obtained in this test provide an indication of the temporary shear stability of the viscosity index improver used in the formulation of multi-grade engine oils. If an engine oil is not able to maintain an adequate viscosity when high engine operating temperatures and high shear rates are encountered wear to critical parts will occur.
HIGH TEMPERATURE HIGH SHEAR VISCOSITY ASTM D-4683D To ensure that an engine oil provides the proper viscosity in order maintain engine durability in high load, severe service applications the SAE and different OEMs have set the following minimum high temperature high shear rate viscosity limits: SAE 15W-40 Limit 3.7 minimum SAE 5W-40 Limit 2.9 minimum SAE 5W-20 and 5W-30 Limit 2.9 minimum SAE 10W-30 Limit 2.9 minimum SAE 20W-50 Limit 3.7 minimum Mack EO-N N Premium Plus-03 4.2 minimum Detroit Diesel Power Guard 4.2 minimum
SHEAR STABILITY All multi-grade engine oils contain some percentage of polymeric viscosity index improvers. When the multi-grade engine oil is subjected to high shear rates, its polymeric viscosity index improvers are either squeezed to a more compact form or align themselves in the direction of motion, reducing the resistance within the oil film. This temporarily brings the viscosity of the engine oil to that of the starting base oil viscosity, thereby reducing fluid friction for better fuel economy or power output.
SHEAR STABILITY When the engine oil leaves the high shear zone, the polymers revert to their former arrangements and the oil recovers its higher viscosity. High shear rates can cause some permanent viscosity loss to take place, when the polymeric molecules are broken into smaller ones which are less viscous. Resistance to this breaking can vary with the type of viscosity index improver used. Some types are more shear stable than others; but there will always be some loss in viscosity.
SHEAR STABILITY Therefore, a multi-grade engine oil should exhibit very little viscosity loss in order for the engine oil to stay within its designated viscosity grade during its useful life. If viscosity losses are too great and the engine oil does not stay in grade due to poor shear stability this can result in: * Increased Oil Consumption * Increased Oil Leakage * Increased Engine Noise * Improper Fuel Injection, Precision and Timing (HEUI) * Increased Friction and Wear
ORBAHN SHEAR TEST ASTM D- D 6278 The Orbahn Shear Test is used to evaluate the percent viscosity loss of multi-grade engine oils resulting from degradation of the engine oil s viscosity index improvers. The engine oil is passed through a diesel injector nozzle at a shear rate that causes the engine oil s viscosity index improvers to degrade. Typically in this test the engine oil is cycled through the diesel injector for 30 cycles in order to closely represent the severity that is seen during engine operation.
ORBAHN SHEAR TEST ASTM D- D 6278 However in the real world there has been a growing concern among OEM s, especially those that produce heavy duty diesel engines that this 30 cycle limit is not severe enough to protect equipment in the field. It has been observed that certain products meeting the 30 cycle limit have been shearing out of viscosity grade during service. Because of this aspect an engine oil that meets API CI-4 4 Plus, Mack EON Premium Plus-03, Detroit Diesel s s Power Guard Engine Oil Specification 93K214 and ACEA E7-04 must stay in grade (Kinematic Viscosity of 12.5cSt @100 C C minimum) after 90 passes.
VOLATILITY CHARACTERISTICS NOACK VOLATILITY ASTM D-5800D When an engine oil comes into contact with the high temperature zones in the engine such as the turbocharger, cylinder walls, valves and the under- crown and ring belt area of the pistons it can begin to evaporate. Evaporation of the engine oil can contribute to oil consumption in an engine and can lead to a change in the properties of the engine oil and the formation of deposits on critical engine parts. An engine oil s s volatility characteristics are directly related to the type of base oil used in the formulation of the engine oil.
VOLATILITY CHARACTERISTICS NOACK VOLATILITY ASTM D-5800D The volatility characteristics of an engine oil as measured by the ASTM D-5800 D Method has been found to correlate with oil consumption in passenger cars and heavy-duty diesel engines. Many OEMs, API and ACEA specifications specify a maximum allowable evaporation loss limit.
NOACK VOLATILITY ASTM D-5800 D LIMITS SPECIFICATION API SL AND SM ILSAC GF-4 MAXIMUM LIMIT % EVAPORATIVE LOSS @ 250 C, 1 HOUR 15% API CI-4 15% API CI-4 4 PLUS 13% Mack EO-N N Premium Plus-03 13% Detroit Diesel Power Guard 93K214 Specification 13% ACEA E7-04 13%
INCREASED OXIDATION PROTECTION MHT-4 4 TEOST (ASTM D-7097) D The MHT-4 4 TEOST Test (ASTM D-7097) D is a laboratory bench test that measures the passenger car engine oil s s ability to prevent the formation of high temperature deposits in the piston rig belt area. In the MHT-4 4 TEOST Test a 10 ml sample of engine oil is continuously passed over a pre-weighed steel Depositor Rod for 24 hours at a test temperature of 545 F F (285 C). The increase in the weight of the rod caused by deposits is used as a measure of oil performance. The pass/fail limit for ILSAC GF-4 4 is 35mg, while the pass/fail limit for API SM is 45mg.
INCREASED PROTECTION AGAINST OVERHEAD CAMSHAFT LOBE WEAR. SEQUENCE IVA TEST METHOD The Sequence IVA test evaluates an engine oil s performance in preventing camshaft lobe wear in overhead camshaft engines. The test simulates taxicab, light-duty truck or commuter service. To pass this test an engine oil must not exhibit no more than average cam wear of 90 micro meters at the end of 100 test hours that consists of 100 hourly cycles consisting of two operating modes that simulate start-stop stop short cycling high idling driving conditions.
INCREASED PROTECTION AGAINST ENGINE CORROSION AND RUST BALL RUST TEST (ASTM D-6557D 6557) The Ball Rust Test (ASTM D-6557) D is a laboratory bench test that evaluates the ability of an engine oil to prevent engine corrosion, particularly the formation of rust under short trip conditions. The test fixture is a custom built bench rig based on a temperature controlled shaker table. A syringe pump is used to inject acid into the oil being tested, while compressed air manifold system supplies clean dry air into the oil at a controlled rate. To pass this test an engine oil must exhibit an average grey scale discoloration value on the hydraulic lifter balls used in the test rig should be rating of100 minimum at the end of 18 test hours and a test temperature of 118 F F (48 C). The higher the average grey scale value the greater an engine oil s s ability to protect against the formation of rust under short trip conditions.
Viscosity The most important physical property of a lubricant. Viscosity is responsible for the formation of lubricating films. Defined as the resistance to flow or deformation. Slower the flow the higher the viscosity. Faster the flows the lower the viscosity.
Importance Of Viscosity Should be high enough to maintain a fluid film The correct viscosity is crucial for optimum performance and extended equipment life. Too low a viscosity: High wear rates High operating temperatures Too high a viscosity: energy is wasted, poor flow characteristics high operating temperatures
Factors Affecting Viscosity Selection OPERATIONAL CONDITION vs. VISCOSITY NEEDED HIGHER LOAD HIGHER TEMPERATURE INCREASED SPEED
Influences On Viscosity Temperature Pressure Shear effects Flow rate Contamination Oxidation Surface roughness
Surface Roughness All metal surfaces no matter how finely machined and polished are covered with a random distribution of peaks and valleys and are rough. Some of the peaks are steep and jagged, other are low and rounded. Some are close together and some far apart. Surface roughness has an effect on friction and wear.
Viscosity Measurements Two common measurements of viscosity are: Absolute viscosity Fluid s s internal resistance to flow and shear caused by internal friction. Kinematic viscosity Fluid s s resistance to flow and shear by the forces of gravity.
Absolute Viscosity Absolute viscosity is the ratio of shear stress by shear rate. The basic unit of measure is the poise (P). The common unit of measure used for expressing absolute viscosity is the centipoise (cp). 1cp = 0.1p. Generally performed by the use of a rotary viscometer. Can be used to readily obtain measurements at very low and very high temperatures. The torque of a spindle determines viscosity in centipoise. Used to determine viscosity where shear rate control is critical. (Brookfield, cold cranking simulator, mini-rotary viscosity and high temperature high shear viscosity).
Kinematic Viscosity Time is takes the oil to travel through the orifice of a capillary tube at a specific temperature. Converted to kinematic viscosity by multiplying the time by the tube calibration constant. Unit of measurement centistokes (cst). ISO, AGMA and SAE grades are based upon kinematic viscosity, Temperatures used are 40 C C and 100 C. cst = cp/ specific gravity (at the temperature determined).
SAYBOLT Universal Viscosity Older measure of viscosity, still used in the united states. Measured as the amount of time in seconds for a specific volume of oil to flow from a reservoir through and orifice of specific dimensions. Units are Saybolt universal seconds (SSU) or (SUS). Typical temperatures used are 100 F F and 210 F. To converts SUS to kinematic viscosity at 100 F F divide by 4.664. To convert SUS to kinematic viscosity at 210 F F divide by 4.632. To convert SUS to ISO grade divide by 5 (i.e.. 500sus/5 = 100 ISO).
Other Viscosity Measurements Engler widely used in Europe. Test method is similar to the Saybolt method but viscosity values are reported as Engler degrees(e ). the test temperature used is 50 C C (125 F). Saybolt Furol the Saybolt Furol operates on the same principle as the Saybolt universal viscometer except that it is designed with a larger orifice to facilitate the testing of very viscous oils such as fuel oil and petroleum resins. Units of measure are Saybolt seconds Furol (SSF). Redwood method used in Europe. Redwood viscometers are similar to Saybolt viscometers. Units of measure redwood seconds. Test temperature used is 60 C C (140 F).
ISO Viscosity Grades (ISO 3448) ISO GRADE MID-POINT VIS @40 C, CsT KINEMATIC VIS RANGE @ 40 c, CsT ISO GRADE MID-POINT VIS @ 40 C, CsT KINEMATIC VIS RANGE @ 40 c, Cst 2 2.2 1.98 2.42 100 100 61.2 74.8 3 3,2 2.88 3.52 150 150 90 110 5 4.6 4.14 5.06 220 220 198 242 7 6.8 6.12 7.48 320 320 288 352 10 10 9 11 460 460 414 506 15 15 13.5 16.5 680 680 612 748 22 22 19.8 24.2 1000 1000 900 1100 32 32 28.8 35.2 1500 1500 1350 1650 46 46 41.2 50.6 2200 2200 1980 2420 68 68 61,2-74.8 3200 3200 2880-3520
R&O AGMA GRADE EP AGMA GRADE ISO GRADE VIS cst @ 40ºC VIS SUS @ 100ºF 1 46 41.40-50.60 193-235 2 2EP 68 61.20-74.80 284-347 3 3EP 100 90-110 417-510 4 4EP 150 135-165 626-765 5 5EP 220 198-242 918-1122 6 6EP 320 288-352 1335-1632 7 COMP 7EP 460 414-506 1919-2346 8 COMP 8EP 680 612-748 2837-3467 8A COMP 8A EP 1000 900-1100 4171-5098 9 9EP 1500 1350-1650 10 10EP 2200 1980-2420 11 11EP 3200 2880-3520
Viscosity Index Viscosity changes due to temperature are expressed as viscosity index. The higher the viscosity index, the less it changes with respect to temperature. All oils increase in viscosity with decreasing temperature and decrease in viscosity with increasing temperature. Change in viscosity with respect to temperature does not respond in a consistent manner.
Typical VI Range For Different Types Of Base Stocks BASE STOCK TYPE VISCOSITY INDEX RANGE Some phosphate esters -20 to 0 Naphthenic petroleum base oils and some types of diesters Paraffinic petroleum and synthetic blend base oils VI Improved oils and synthetics 0 to 70 80 to 135 100 to >200