to full operating temperature in cold weather. As a point of reference, Mercedes restricts engine · performance at oil temperature

to full operating temperature in cold weather. As a point of reference, Mercedes restricts engine performance at oil temperatures below 20°C (68°F) on AMG models.60 Just as Al-Si engines can be negatively affected by cold weather operation, at higher engine temperatures the minimum oil film thickness (MOFT) required varies depending on the regime of lubrication (hydrodynamic, mixed, or boundary) as well as the oil used. The struggle for engineers seeking higher fuel economy is that higher viscosity oils cause higher viscous power losses, requiring either higher operating temperatures or thinner oils to reduce these losses. Higher oil temperatures resulting in lower lubricant viscosity help to reduce oil intrusion into the combustion chamber as well as evaporation and consumption, reducing the likelihood of low speed pre-ignition (LSPI) in direct injected, forced induction engines. Controlling liner temperatures have a direct effect on surface lubricant temperature, HC, and NOx emissions, so an optimal temperature has to be found to balance emissions as well as thermal and frictional losses. Frictional losses from the piston rings are at their lowest with a liner temperature of 80°C (176°F)., but at higher temperatures, MOFT may transition lubrication from mixed to boundary layer, causing increased friction due to asperity contact, such as the plastic deformation of the aluminum matrix of Al-Si bores. A temperature increase of the liner from 80-120°C (176-248°F) can result in a 40-55% reduction in MOFT mid-stroke, in areas where bore scoring can occur. In fact, once operating in boundary lubrication regime, an increase of temperature has little effect in the MOFT, and it is the anti-wear additives like ZDDP and moly that provide the needed wear protection for these surfaces in the cylinder system.61 With both extreme hot and cold operation, driving short distances, as well as mixed city and highway driving, determining oil change intervals (OCI) is quite the challenge. With modern synthetics, most manufacturers have extended their OCI to multiple years and 15,000 miles or more. GM in conjunction with their DEXOS oils that are calibrated to their oil life monitoring system, utilize an oil health monitoring system that continuously monitors engine-operating conditions.62 The system has proven itself to be very accurate at estimating the remaining life of the engine oil to determine when to change oil. However, most manufacturers still utilize time or mileage limits, whichever comes first. Some provide severe service intervals, typically three to six months and 3,000 to 5,000 miles, and is especially important for vehicles operated in colder and hotter climates alike.63 Even with a system as advanced as GM’s oil life monitor, the only way to accurately measure an oil’s performance for a given application and the component health lubricated by an oil is with regular used oil analysis. In Al-Si engines, knowing the primary wear metals from the cylinder bores would be comprised of aluminum and silicon, regular testing can provide a baseline wear profile for a given lubricant and engine combination. Not only is it possible to validate changes to OCI and the effectiveness of lubricants used, but also to detect accelerated wear of the aluminum matrix and silicon particles that support the Al-Si cylinder system. 60 2015 Mercedes S-Class Sedan Operators Manual. Driving - pg 189. Mercedes Benz USA. 61 The effect of cylinder liner operating temperature on frictional loss and engine emissions in piston ring conjunction. R. Rhamani, et al. Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, Loughborough, Leicestershire, UK. 62https://assets.cobaltnitra.com/teams/repository/export/975/c7820afba1004895010145efa6b30/975c7820af ba1004895010145efa6b30.pdf 63http://www.hastingsfilter.com/Literature/TSB/94-1R1.pdf LN Engineering Technical Library. Copyright ©2019 LN Engineering LLC