LubricantConsumption

Every day thousands of vehicles undergo a check for engine lubricant levels. There’s much wastage out there, magnified by ignorance, fraud and with an environmental impact. Let’s clean up! Dave Scott, FleetWatch Technical Editor reports. 

Checking engine lubricant consumption is monitoring engine life – it starts at the dipstick. What appears to be a simple, menial task is important, requires both training and understanding, and must be executed in absolute cleanliness. Cummins engine guru, Marius de Lange, observes that premature engine failure has been tracked down in some instances through grime introduced through a dipstick, and this especially in the Middleburg area where coal-haulage road conditions leave everything coated with sticky muck. 

DIPSTICK AND FILLER NECK  A typical dipstick and engine-lube filler neck are located next to each other. It's right here that untrained dipstick readings are taken and contaminants - just plain road dirt or cloth lint - are unwittingly introduced into an engine. This area must be inspected for cleanliness

CHECKING THE LEVEL The moment of truth and accurate judgement - what is the engine capacity in this dipstick between low and full - is it as much as five litres? How much should be topped up? Should it be left for another trip to get to the low level? Is it increasing due to fuel dilution? Was the 'cleaning' rag lying on the floor?

A line-haul truck tractor in SA operating conditions is expected to achieve no less than 850,000km prior to first engine overhaul and overfilling engine-oil or sloppy dipstick hygiene can easily drive this down to 600,000km or even less than that. 

Motorists pride themselves on the fact that their car ‘doesn’t even use oil’. Any engine is expected to use lubricant. According to the owner’s handbook, a 1,5 litre Honda petrol engine that equips the Jazz model can use up to one litre of oil in 1000km. And a hard-working truck diesel will consume more than that as top-up litres can match fuel consumption at a ratio of up to 0,5% of total fuel used – 5 litres to 1000 litres of diesel which in long-distance haulage means one-way to Cape Town from Mussina on the Limpopo border. High lube consumption matches high fuel consumption. Exceeding the 0,5% benchmark on a truck means there’s something seriously mechanically wrong, or either negligent dipstick-level reading or fraudulent ‘skimming’ is occurring, such as: 

• Deliberate over-filling – to increase lubricant turnover.

• False reading of dipstick levels to ‘skim’ the extra lubricant left when a dipstick indicates the correct level. 

PATRICK SWAN Failure analysis expert Patrick Swan - "Always ensure a dipstick is clean and lint free. Dipsticks that have a measuring notch can snare cleaning cloth that goes unobserved and are reintroduced into an engine via a dipstick. For example, addition of lint through daily lube checks into a CAT D9 bulldozer engine blocked the oil supply to one main bearing causing serious engine failure. And then there's just plain dirt that forms a grinding paste while lint blocks oil galleries."

Technical reasons for engine damage

Too high a level of lubricant in an engine sump, by overfilling or incorrect calibration of the level indicator (dipstick), causes the crankshaft and connecting rod big-end caps to whip up the lubricant into all-pervading foam where damage ensues. An aerated-oil mixture is forced into the bearings and as air is not a lubricant, the foam has a low load-carrying ability. Excessive foam build-up in a reservoir or sump rapidly leads to excessive wear and catastrophic system failure. Air leaks into the oil flow or an open drop from a supply pipe into a hydraulic fluid reservoir can generate foam. Operationally, engines must never be overfilled, the level indicator must be accurate, leaks stopped, and supply pipes extended to deliver return lubricant below normal liquid surface level in a sump reservoir. 

On the other hand if the lube level is too low then low oil pressure may be encountered and this would result in engine damage to the main crank, big ends and crankshaft. 

JOHN FITTON John Fitton, fuels specialist - "Froth control is critical - carefully formulated engine oils are designed to release the entrapped air from the engine oil, but it is formulated for normal operation where the air entrapment is limited. Excessive "beating" of the lube by the crankshaft in the sump due to over-filling will result in the anti-foam additive not being able to cope."

The overlooked engine breather’s role

A crankshaft creates a heavy oil mist that leaves through a breather that on modern engines exits into the airflow before the turbocharger – if it entered after the turbocharger the turbo would pressurize the sump! Abnormal lubricant volume in the turbo will deposit on the impellor blades, unbalancing the turbo and resulting in failure. Extra oil can also partially block the intercooler leading to lack of power and increased fuel consumption. Excessive lubricant can also enter the combustion chamber where it burns and the engine can run on or run away. Worse still the excess pressure created can blow an oil seal. 

A hot truck engine cylinder head holds many litres of lubricant when switched off – in some cases the recommended wait period prior to checking the engine sump dipstick is at least 10 to 30 minutes depending on engine design and sump capacity. 

It sounds almost too basic to be true but engine lube levels must be checked when a vehicle is on a level surface. Also some systems, such as automatic gearboxes require the lubricant level to be checked while the engine is running. 

But what happens when a dipstick indicates an increase in engine lube levels? Does this get noticed and reported? When this is noticed, action must be taken to determine the root cause of the high level – was it due to the over filling of the sump with engine lubricant or is it possibly fuel dilution in which case the sump should be drained and the problem determined. 

CLEANING RAG Here's a typical fuel fill point where a cleaning rag for fuel cap and dipstick is left on the ground to introduce contamination and wear into an engine.

The dipstick that was too short

A new truck was measured as using too much oil. Before the engine was to be stripped down a visiting service manager asked for a spare dipstick from the parts division to be compared to the dipstick already in the engine and used as the measuring device for excessive oil consumption. The wrong dipstick was present in the motor and being too short, the engine was overfilled every time while blowing out the excess oil on every trip - the correct dipstick solved the problem without a costly, and fruitless, engine teardown. 

The difference between the low and full mark on the dipstick of a Cummins ISX line-haul engine is as much as eight litres, after waiting for 10 minutes for a hot engine to settle down. What yardstick measurements will a driver or pump jockey use to top up – will it be to overfill to be on the perceived ‘safe’ side? Very few drivers or pump jockeys really know the consequences of their actions. Overfilling is a national truck fleet evil and an environmental problem. It’s time for executives to leave their computers for a moment and walk around during ‘top-up time’. You might get a nasty surprise!