Today’s high-viscosity lubricants act fast to protect an engine’s components. John Lewis reports on the bus industry’s unsung heroes
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Modern lubricants look thin to the point of transparency by comparison, yet the technology they contain provides vulnerable moving parts with valuable protection.
Unfortunately, the role they play is regularly ignored says John Walters, Global Fleet Sector Marketing Manager at Shell Lubricants: “Vehicle availability, maintenance costs and fuel expenditure all influence a fleet’s cost per kilometre, but the impact of lubrication on these critical factors is too often underestimated,” he observed.
Lubricants have plenty of work to do. As well as acting as a protective barrier between the piston and cylinder liner they are expected to control sludge, disperse soot, act as a coolant and protect the engine against corrosion as the oil starts to oxidize.
All oil suppliers agree that there is a marked trend in favour of low-viscosity synthetic engine oils as manufacturers concentrate on improving fuel economy, shrinking the carbon footprint of their products, and cutting harmful emissions.
Lubricants have to assist in the achievement of all three goals.
“We’re increasingly seeing fully-synthetic low-viscosity 5W-30 lubricants being specified,” said Rob Lundie, Technical Services Manager at Exol Lubricants.
“They flow quickly around the engine the minute it starts and create less drag, so you get immediate fuel economy benefits.”
The trend seems to be accelerating, he added: “0W-20 grades are now being trialled by Scania.”
Such grades are not new, points out Shawn Whitacre, Senior Staff Engineer, Heavy Duty Engine Oil technology at Chevron Lubricants: “Products such as 0W-20 have been in use for a while, but their ability to perform in a wide range of applications is still not clear so far as durability is concerned,” he said. “As a consequence, the industry is taking a cautious approach towards them.”
Last year saw Chevron launch a new range of lubricants for commercial vehicles, including coaches and buses, under the Texaco Delo banner.
Handy savings
Two major European fleets have reported useful fuel savings after switching to ExxonMobil’s fully-synthetic Mobil Delvac 1 LE 5W-30, says the oil producer.
A German operator with 210 vehicles has notched up an average 2.1% cut in diesel usage, while a French operator has reported a 3.2% reduction after trialling the same lubricant in two vehicles for 12 months.
The duo’s sumps were previously filled with a standard 10W-40 and the change has resulted in an overall fuel bill cut of almost £5,600 says ExxonMobil. It goes on to calculate that the German fleet could potentially save £240,000 a year.
“There are many factors that influence the specific fuel economy advantage offered by lower-viscosity engine and driveline fluids,” said Shawn. “Most notably, the duty cycle of the application greatly affects the percentage improvement that can be expected.”
He goes on to suggest that low-viscosity oils could bring greater fuel economy benefits to vehicles on short-haul stop-start work than to those maintaining a steady speed on inter-urban runs.
Whereas the former could see diesel consumption fall by up to 4%, the latter may see an improvement of no more than 1% to 2%. Even this modest saving is of course still worth having in an era of pinched profit margins.
Low-viscosity synthetics can potentially result in low oil pressure, especially if a vehicle spends a lot of time in stop-start big-city traffic.
“They can also lead to fuel dilution problems,” said Bob Wood, Technical Engineer at Total Lubricants. That is where unburned fuel gets mixed with oil in the engine crankcase.
As a consequence they have to be formulated in such a way that such difficulties do not arise, while at the same time being asked to do more with less.
That’s because sumps are smaller than they used to be, and the oil they contain has to be capable of coping with the higher engine operating temperatures associated with Euro VI.
Downsizing engines with an eye to saving weight and cost is leading to higher oil temperatures too, says Shawn: “There are undoubtedly demands for better high-temperature performance.
Running engines hotter has upped the ante so far as additive performance is concerned, requiring more potent antioxidant chemistry to further enhance product stability and long oil life.
“We have to formulate oils that don’t break down – thicken and become acidic – when exposed to high-temperature operation.
“Products meeting these new specifications, including Delo 400 XLE SAE 10W-30, must comply with the rigorous demands of the high-temperature Volvo T-13 test, introduced as one of the first diesel oxidation tests utilised in a heavy-duty performance category,” he continued. “We expect these demands to be incorporated into next-generation ACEA requirements as well.”
The most common cause of oil degradation, oxidation, is a chemical reaction that occurs when lubricating oil and oxygen combine and is accelerated by high temperatures.
An oil’s oxidation stability is a measure of its ability to resist this reaction.
SAE refers to the Society of Automotive Engineers, which sets standards in a variety of automotive areas. ACEA denotes the European Automobile Manufacturers’ Association.
“New engines tend to produce much less lube oil soot than their predecessors, which has led ACEA to tone down its soot control requirements,” Shawn said.
Longer lasting
Lubricant has to last longer too.
“Drain intervals have gone up by 50% over the past 10 years,” Rob Lundie said.
It is a trend that has benefited coaches as well as buses
If they are on urban work, however, their sumps usually have to be drained twice as frequently as those of vehicles that spend most of their time on dual carriageways and motorways.
Conscious that this is the case, at least one bus manufacturer has come up with oil change intervals that depend on a vehicle’s average speed.
Many operators run Euro V, Euro IV and often even older vehicles alongside their modern Euro VI line-up.
So, can more modern oils be used safely in older engines? In some cases, yes.
Millers Oils has recently introduced a fully-synthetic lubricant called Trucksynth 10W-40 which can be used in Euro IV and V as well as Euro VI diesels.
“Scania recently came up with a new specification – LDF-4 – which allows a 5W-30 to be used in coach and bus engines that go all the way back to Euro I,” Rob Lundie said.
“Manufacturers vary in terms of how they view backward compatibility though,” Shawn pointed out. “Some are very accommodating, but others are much more restrictive.” These restrictions could get tighter in future as the swing towards low- and ultra-low viscosity lubricants gathers pace.
“Looking at potential future standards, it is likely that lower-viscosity HTHS (High Temperature, High Shear) oils will not have backwards compatibility for older engines,” he said. HTHS lubricants are designed to perform well at both high and low temperatures.
“We’ve already begun work on a future generation of products designed to align with future manufacturers’ needs,” he added. “They will go even further in terms of helping to reduce CO2 emissions.”
Modern fully-synthetics are of course comparatively expensive – something that should be taken into consideration if you are going to use them in an older diesel.
“It could mean you get better fuel efficiency though,” Rob Lundie observed.
Cleaned out
“Remember though that a modern synthetic may clean an older engine out so thoroughly that you lose compression and burn more oil,” Bob Wood commented – which could go some way towards defeating the object of the exercise.
The degree to which intervals can be stretched and fuel economy improved is illustrated by a decision made by Bicester, Oxfordshire-based Grayline Coaches back in 2017.
Working with independent lubricants supplier Race Group, it decided to switch away from mineral-based oils in favour of fully-synthetics across its 19-strong fleet.
Grayline began by using fully-synthetic Castrol Transmax Z in an Allison automatic gearbox; the lubricant is suitable for use in both fully- and semi-automatic transmissions in coaches and buses.
It was happy with the results, and Race then recommended the use of fully-synthetic low-SAPS (Sulphated Ash, Phosphorus and Sulphur) Castrol Vecton Long Drain 10W-40 in the fleet’s engines. Fully-synthetic Castrol Syntrax Longlife 75W-90 was recommended for the drive axles.
Average drain intervals have been extended from 8,000km to 24,000km as a consequence and the operator’s fuel bill has fallen by more than £38,000 a year.
It is worth noting that the fleet is made up of vehicles of different ages, makes and models, each of which covers more than 24,000km annually.
Race Group is part of Certas Energy, a major independent distributor of fuel and lubricants. It delivers over 6bn litres of oil to UK customers every year.
Already supplying operators in the Midlands and north of England with Castrol lubricants, Race recently signed a five-year agreement to supply fleets in the south of England too.
At the time of writing it was about to open a new depot in Kingswinford in the West Midlands.
The reference to SAPS is an important one.
“Requirements that have been in place for over 10 years demand a balance between oil performance and emission control system protection,” said Shawn.
“They limit the amounts of sulphated ash, phosphorus and sulphur that can be used in heavy-duty engine oil formulations.
“Our Delo 400 XLE SAE 10W-30 even meets the more restrictive requirements of ACEA E6, which includes a tighter phosphorus specification,” he added.
Chevron is using ash-less non-metallic components in its oils so as not to compromise a vehicle’s emission control system.
“They still give you decent fuel economy and a decent drain interval,” Shawn said.
Final drive
The emphasis placed on the importance of selecting the correct transmission and axle oils by Race and Grayline is well-founded.
The former can make a significant contribution to fuel economy if a vehicle is on stop/start work, says Shawn, while the latter comes to the fore on long-distance motorway runs.
Fuchs Lubricants has not long launched a new transmission oil under the Titan ATF 5500 banner.
It makes the point that in recent years manufacturers have managed to extend transmission oil change intervals from somewhere between 30,000kms and 60,000kms to 120,000kms and even as far as 180,000kms.
Suitable for ZF Ecomat boxes, and part of a family of new lubricants, Titan ATF 5500 can cope with these long intervals says the company.
It can be used in ZF EcoLife boxes for up to 120,000kms, it adds, and in Voith DIWA boxes for up to 180,000kms.
Global lubricants manufacturer Fuchs has been investing heavily in its UK facilities, spending over £10m on manufacturing equipment and a new raw materials warehouse that can hold 4,000 pallets.
It is also continuing to develop its technical centre.
Extending oil change intervals brings environmental benefits, with less waste oil and fewer used oil filters to dispose of.
It is also worth mentioning that used waste oil is a carcinogen and should always be treated with care in a workshop.
Technicians should avoid getting it on their skin and should never make the mistake of absent-mindedly stuffing rags soaked with it into the pockets of their overalls.
The less waste oil there is around, the less likely it is that it will end up in a pool on the workshop floor leading to somebody slipping in it and suffering an injury.
Such spillages should of course always be cleared up immediately.
Stretched drain intervals could prompt some operators to wonder just how well the lubricant they are using is really performing after umpteen thousand kilometres of arduous service.
If they are uncertain, or suspect there may be a problem with the component being lubricated, then having the oil analysed could be a sensible precaution.
A number of oil companies can offer an analysis service including Total under the ANAC (Analysis Compared) banner.
Returning to Trucksynth for a moment, Millers makes the point that it meets the requirements of a long list of vehicle manufacturers and engine suppliers standards, including MAN M 3477, Volvo VDS-3 and Cummins CES 20076 and 20077.
It is clearly important that any lubricant used in an engine has the appropriate approval, and companies such as Millers have technical departments that can advise operators accordingly.
Some buses are in service in the UK that run on compressed natural gas, while last September’s IAA Hanover Commercial Vehicle Show in Germany saw Scania unveil a long-haul coach that runs on liquefied natural gas.
The Interlink Medium Decker offers a claimed range of over 600 miles.
On the face of it, lubricants should last longer in engines that use gas because it burns more cleanly than diesel.
“Gas engines run hotter though, so oxidation stability is more important,” Shawn pointed out. “They also tend to rely on spark ignition, which imposes limits on some of the additives that can be used.”
At least they still use lubricants.
With electric motors rather than internal combustion engines, the demand for them from battery-powered buses is going to be comparatively modest – something which may start to give automotive lubricant industry executives sleepless nights if it isn’t doing so already.
While fully-synthetic oils can bring cost savings, they do not come cheap; and tight constraints on maintenance budgets can sometimes oblige hard-pressed workshops to seek cheaper alternatives to save cash.
That would be a false economy, however, says Shell’s John Walters. “Always remember that the detrimental effect of cheaper oils and greases on equipment can prove more expensive over time,” he observed.
Being forced to replace an engine prematurely because it was run on bargain-basement lubricant can easily wipe out any savings that appear to have been made; and if a coach or bus is off the road having its engine changed, then it is not earning the operator money.
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