Sep

Lubrication… less is better

2010-09-12 16:24

When it comes to lubrication, the attitude is that ‘˜more is better’. Nothing could be ‘˜more’ technically incorrect writes our technical correspondent Dave Scott who urges operators not to just ‘˜throw’ lubricants at a truck.

There is a distinct lack of training and information when it comes to lubricating a truck. How often have you seen excessive greasing of fifth wheels leaving lumps of grease spattered all over the chassis and on the road , a hazard to other road users and a blot on the environment? And while you may think that overfilling engine oil levels is a good thing, not so. It will damage the engine. In the driveline, gearbox and differential, similar problems occur.

One glance at chassis springhangers, where excessive grease is forced out beyond the seals and revealed, is enough to tell you that the whole truck has also been abused in this way. The consequence is that seals are damaged and attract contamination. Other visual evidence of overfilling is found in breathers that are discharging excessive lubricant.

So what’s the technical reason for strictly observing the correct lubricant levels in engine gearbox and differential sumps? Tribology & Lubrication Technology magazine carried a clear answer in the April 2010 issue. “When the sump level is too high, the oil can be churned and aerated by themoving components, leading to air entrainment…and air contamination warrants immediate attention.’

Here’s the crunch: “Air has no load-bearing capability and when compressed, air creates tremendous heat. For a machine serviced by an oil bath, the collapse of the oil film as bubbles pass through the component interfaces causes surface wear and destruction and sets components on a path to failure. For circulating systems, as an air bubble passes through the pump, the bubble is compressed to system pressures. As the bubble collapses, it creates enormous heat, potentially causing flash vaporization of the oil around the super-heating bubble.’ Phew! And you thought you were building in a safety margin by overfilling.

Whose job is it to check engine oil levels in the morning? The only time for this is when the engine is cold and has not been started as reading a dipstick when the engine has already run may give a false reading as lubricant is trapped in the top of the engine and takes time to drain down. It seems natural for this check to be left to drivers but do drivers ever report that a dipstick records overfilling? Most likely never!

Do drivers ever report that engine oil levels are rising on an engine dipstick? This is really serious as engines do not ‘˜manufacture’ oil and it could mean there is contamination and dilution from either the coolant or diesel fuel. It would seem that multiple drivers on one truck would confuse responsibility for this task. So who really carries out the check and how well trained are they?

This industry needs to raise expectations for lubricant applicators and ban the term ‘˜grease monkey’. Training also needs to be introduced as an on-going issue. The problem is that fleets have many different lubrication requirements and it’s an exact science.

Finally, measuring oil consumption is not negotiable – per vehicle and in relation to fuel consumption. Hard-working engines use fuel and will use oil. It’s not a question of one-size-fits-all. Reading a dipstick has become so subjective that it’s time for the electronic age to take over as electronic sensing seems a far more attractive proposition than someone using poor judgement and overfilling. A dipstick reading three-quarters full is far better than overfull.

Remember – less, not more, is better!

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