ON THE JOB
Motor Oil Is Hydraulic Fluid
All of today’s police engines (all of them) have a variable valvetrain or lifter-controlled cylinder deactivation. The Charger’s 5.7L V8 and the Tahoes 5.3L V8 have both. All these engines depend on the motor oil to act like hydraulic fluid…and the two are not the same!
All of this places great importance on the oil. Motor oil has always been used to lubricate and to cool the engine. Variable valvetrain systems, and that especially includes MultiAir, place a third demand on motor oil: It must now also act as a hydraulic fluid.
On any engine with a variable valvetrain or cylinder deactivation, the wrong weight of motor oil, or dirty oil that has consumed its anti-foam additives, can throw a Diagnostic Trouble Code or Malfunction Indicator Light. That is because the hydraulic oil properties are not what the powertrain control module (PCM) expects them to be.
The PCM expects the variable valvetrain to respond in a certain way. If the oil has mini-bubbles in it, or is too thick or too thin, the valvetrain will not do what the PCM tells it to do and when it tells it to do it. The PCM will sense trouble…and let you know about it.
The advantages of synthetic oil in police work are clear. Synthetic oil offers better engine protection during a cold start, when 60 percent of engine wear takes place. Synthetic oil also offers better protection in extreme cold, extreme heat, and during periods of extended idling…you know, routine police work.
Synthetic oil increases the oil change interval to between 10K and 12K miles. Synthetic oil costs more than conventional petroleum oil. However, with the extended drain interval, synthetic oil is actually a cost savings of around $110 per vehicle per year.
Get up to speed on synthetic oil because most 2011 and new GM vehicles require the use of dexos™ motor oil. Oil meeting the GM dexos oil spec is essentially synthetic oil. In some cases, the synthetic motor oil already meets the dexos spec. Think Mobil 1. In other cases, a tiny amount of expensive molybdenum needed to be added for increased anti-wear control. This element may be in addition to, or in place of zinc, the most common anti-wear compound.
The GM dexos spec is merely a year or so ahead of the oil industry’s new GF-5 oil spec. GF-5 will replace GF-4. These specs are developed by the International Lubricants Standardization and Approval Committee (ILSAC) with input from automakers, oil refiners and additive makers. For those more familiar with the American Petroleum Institute (API) rating system, the new ILSAC GF-5 will carry an API “SN” label.
The move to synthetic oil was coming anyhow. GM dexos just got the jump on the rest of the industry. The new GM dexos, ILSAC GF-5 and API SN oils are superior in almost every way to conventional, non-synthetic motor oil.
The GM dexos oil has one spec that ILSAC and API labeled oils do not have. This is quite important! That dexos requirement is for better resistance to aeration, which is the whipping of air bubbles into the oil. Engines with variable valvetrain (variable camshaft timing) technology use engine oil as a hydraulic fluid to move components in the engine, i.e., hydraulic lifters.
If air bubbles are in the oil, the lifters will not act as fast as the engine controllers expect. On the mild end, this can limit engine performance and economy. On the extreme end, this slow response can throw a MIL or DTC check engine code. Chevy, Dodge and Ford police vehicles all use engines with a variable valvetrain timing!
For all practical purposes, put Mobil 1 in all GM police vehicles. The use of synthetic oil has always been a good match for how we use our vehicles. Now, according to GM, it is a requirement.
Oil change intervals must be followed on any engine with a variable valvetrain. The exact oil on the filler cap must be used, both weight and blend (petroleum, synthetic blend, and full synthetic). Motor oil is responsible for 100 percent of the engine lubrication, 40 percent of the engine cooling, and 100 percent of the hydraulic action. Use the right oil. Change it on time.