H.D. Oils Lengthen Engine Life L.T.E. Experiments Prove Higher Cost
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of Detergent Oils is justified HEAVY-DUTY oils were proved in a three-year test conducted by the London Transport Executive with oil-engined vehicles to increase mean engine life by 7.7 per cent., compared with the use of plain oils, and more than to justify their higher cost. This was revealed by Mn Wilford in a description of three tests with heavyduty oils made by the Executive from 1944 onwards.
At the outset, he pointed out that the early objections to heavy-duty oils— their higher price, the difficulty of determining the proper oil-change period, the removal of the additives by certain types of filter and reclaiming processes, and the reintroduction of a "mystery element "—remained. " But," he said, "the evidence in their favour is such that bus and coach operators cannot afford to overlook them. On the other hand, the change from plain oil to H.D. oil is not one that should be lightly undertaken."
Ash Content
Because of the metallic constituent of the additive, an H.D. oil left an appreciable residue after ignition. In oils of the American specifications 2-104B or M1L-2104, the residue (ash content) might be as much as 0.4 per cent. Although this amount of ash was larger than in a plain oil, it did not cause trouble in use.
An H.D. oil was, said Mr. Wilford, claimed to clean the engine by preventing deposits from accumulating. It would also dislodge existing deposits. If a detergent oil were introduced into an engine which had been running for some time with a non-detergent oil, there was a risk that deposits might be carried into the circulating system, and block oilways and choke filters. Engine seizures might, therefore, be caused.
Care was required in changing over from plain oil to a detergent type. Briefly, the procedure followed by the L.T.E. was: (a) To drain the engine base while the oil was hot, preferably c16 immediately the vehicle ran in after a period of service; (b) remove and clean the oil-filter element; (c) refill with RD. oil; (d) mark " HD." on the filler cap and on the engine casing; (e) top up as necessary with HD. oil; (f) after not more than 1,000 miles, drain the base while the oil was hot and remove and clean the filler element; (g) refill with H.D. oil; (b) continue to top .up with H.D. oil; (i) after draining for a second time (after maximum of 1,000 miles) change the oil at the normal periods, also cleaning the filter elements.
Describing the three tests, Mr. Wilford said that the first was started in August, 1944, and was continued until 1947. It involved a garage fleet of about 120 oil-enginecl vehicles.
During the first year of the test, engine bases were drained at 12,000-mile intervals. Afterwards, oil changes were made every 6,000 miles. Engines put into service after the introduction of H.D. oil and removed for overhaul during 1948, were found to have yielded a life of at least 15 per cent, greater than that obtained after their first overhaul and when lubricated with a non-detergent oil.
It seemed fair to conclude that this minimum increase in life of 15 per cent. was attributable to the use of H.D. oil as lubricant," said Mr. Wilford.
Meanwhile, another test had been put in hand with 24 newly overhauled A.E.C. 7.7-litre direct-injection engines. Twelve of the units, all at one garage, were lubricated with H.D. 30 oil, and the other 12, based on another garage, employed non-detergent oil.
' The engines lubricated with H.D. oil yielded a mean life 33 per cent, greater than that of the 12 units using plain oil. The mean rate of cylinder-liner wear was also significantly lower in the engines using H.D. oil than in those lubricated with non-detergent oil.
Cost Calculations
At this stage, calculations were made to determine the minimum extension in engine life that would have to be obtained to compensate for the increased price of H.D. oil, compared with plain lubricant. It was first assumed that "engine lubrication cost" consisted of the total cost of the oil used and the cost of overhauling the engine at the end of its life. From these data, an "engine lubrication cost" figure per week or per 1,000 miles, or on any other basis, could be derived.
For example, with engine oil at 4s, a gallon, a mean oil-consumption rate of 500 m.p.g. throughout the life of the unit (assumed to be 100,000 miles) and with an overhaul cost of £100 per engine, the "engine lubrication cost" per 1,000 miles would be £40 (200 gallons of oil at 4s. per gallon) plus £100 (overhaul cost), giving the total of £140. Dividing 100 into £140, the "engine lubrication cost" per 1,000 miles would be LI 8s.
To justify the adoption of the more pensive lubricant the "engine lubrition cost" per 1,000 miles must main equal to or less than the hypo• etical figure of Li 8s, fin his paper, r. Wilford gave the formuhe em' oyed in arriving at the figure.] In the Executive's case, the calculams were a little complicated by the et that plain oil drained from engines is being recovered, and the cost of e mixture of fresh and reclaimed oil ed at garages was less than the purase price of the fresh oil. Moreover. was uncertain whether H.D. oil could ; reclaimed.
In one set of calculations, it was surned that the used H.O. oil would disposed of in heating boilers, and it is valued at the current price of Ymestic fuel oil.
Overall Saving
These calculations showed that at 48 prices (when H.D. oil cost the cecutive about Is. 6d. a gallon more an plain oil), and assuming a mean 1-conUmntion rate of 300 m.p.g. and e disnosql of used HD. oil as boiler el. engine life would have to be creased by only 8 per cent, to "break en." If the used HD. oil could be covered, an extension in engine life of ay 6 per cent. would be adequate. was found, however, that H.D. oil irld be reclaimed.
Towards the end of 1948, the chief echanical engineer (road services) cided that H.D. oil should be adopted ✓ all compression-ignition engines in e fleet.
Late in 1947, a third service test was irted and continued until 1949. This nbraced . all oil-engined vehicles )eralsog from three garages. A fferent make of H.D. oil was used by ch depot. The engines concerned were A.E.C. 7.7-litre direct-injection toroidal-headed types of various ages.
For comparison, the vehicles at six other' garages were selected to provide data on the use of plain oil.. Information was obtained relating to 484 engines lubricated with H.D. oils and 1,24) with plain oil. The mean life of an engine from the H.D. oil group was found to be 73 per cent, greater than that of engines from
the " " garages. At prices ruling at the end of 1950, it was established that an engine-life increase of 2.7 per cent. was sufficient to give an "even break." H.D. oil was yielding a net saving equal to an extension of 5 per cent. of engine life.
Mr. Wilford explained in detail why the two earlier tests produced so much greater increases in engine life than the final test, which was regarded as conclusive.
The first test was based upon a comparison of the mean life of engines removed during 1948 with that of units removed in 1943 to 1944. The second test was far too small to yield a conclusive result. The favourable result obtained in it arose partly from the fact that among the 14 experimental and comparison engines concerned, only one was removed after a mileage of less than 42,500.
A 'Critical Mileage
"This mileage of-42,500 (or 50 weeks in service) is a critical one, in that from the analysis of data relating to the 484 engines involved in the final test with HD. oil, it was established that the benefit of the detergent lubricant was apparent only in engines which survived for 50 weeks or more," said Mr. Wilford. "If, therefore, mean engine life is estimated from mileages of all engines removed for whatever cause, it is evident that the fewer engines that fail below 42.500, the greater will be the percentage extension of mileage attributable to the use of H.D. oil."
Mr. Wilford thought that the sulphur content of fuel was another important factor to be taken into consideration. Up to about the end of 1947, the Executive was receiving a fuel having a maximum sulphur content of 0.5 per cent. During the final test, the sulphur content was increasing and sometimes reached 1 per cent., and in one instance 1.06 per cent.
" It seems not unlikely, therefore," Mr. Wilford commented, "that the less favourable result yielded by the test which was completed in 1949, is at least partially accounted for by the increase in sulphur content of the fuel."
New Additive Oils
Two new types of additive oil had been developed in the U.S.A. for use in conjunction with low-quality road oil fuels. One of them, designed to meet the specification requirements of the U.S. Ordnance Supplemental List I, was already in limited supply in the United Kingdom, and was advocated for use with straight distillate fuels containing up to I per cent, of sulphur.
Fuels with this content were now in fairly common supply and, said Mr. Wilford, "it would seem that, having worried for years about the desirability, or otherwise, of adopting the ordinary H.D.-type oil, and perhaps having already taken the plunge, operators he got to start thinking about Supplement 1 oils. This is certainly what London Transport are doing, and by the time this paper is presented, we shall have commenced a test involving about 500 engines, spread amongst three garages."
The experiment was being planned on the lines of the 1947-49 test, with certain improvements.