Thin Oils Give Extra Power Output and Mileage
If you've noticed an error in this article please click here to report it so we can fix it.
THE increasing use of low-viscosity oils and the more widespread adoption of additive-type oils, marked two readily discernible trends in engine lubrication in recent years. Mr. F. Lawrence, A.M.1.Mech.E., of Shell Mex and B.P., Ltd., told the Scottish Centre of the Institute of Road Transport Engineers.
in bench tests, using a Leland 9.8litre oil engine, it was shown that increased output was obtained when a drop in viscosity was made from S.A.E.30 to S.A.E.5w. The gain in la.h.p. at 85°C. jacket temperature, when dropping from S.A.E.30 to S.A.E.20, was about I per cent. From
S.A.E.20 S.A.E.10w the figure was about 1.5 per cent. and from S.A.E.I0w to S.A.E.5w slightly below 1 per cent.
With the very light oil, some part of the further increase (from S.A.E.10vv to S.A.E.5w) might have been achieved by burning lubricant as fuel. Such factors as increased blow-by, caused by a poorer gas seal with some piston assemblies might tend to operate against the oil under certain service conditions.
Gains in fuel consumption, obtained with adjustment of the fuel-pump rack setting to give the designed power output for the S.A.E.30 oil, at 85°C. jacket temperature, showed a saving of 2.23 per cent, when dropping from S.A.E.30 to S.A.E.20; 3.29 per cent. from S.A.E.20 to S.A.E.10w and ro further saving from S.A.E.10w to S.A.E.5w.
Mr. Lawrence concluded from all the tests conducted that worthwhile improvements in both power output and fuel economy could be obtained in high-speed oil engines with a reduction of lubricating oil viscosity.
Ring-wear tests conducted on a Gardner single-eylindered 1.39-litre oil engine showed that wear increased with straight oils when the viscosity was decreased and the load increased. With an appropriate additive oil, wear was significantly less than with straight oils at all viscosity and load levels.
An S.A.E. lOw H.D. oil at the additive level employed (M1L-0-2104), at normal operating temperature-85°C. —showed less wear than the S.A.E.30 grade of the, same oil, and about one-eighth that experienced with the S.A.E.30 straight mineral-base oil (95/100V.1.). Contrary to expectations, ring wear had been found at least as good, If not better, than with heavier oils, and liner wear had decreased.
Crankshaft, journal and bearing wear, as far as could yet be ascertained, had not been adversely affected. These results had been obtained without any disturbing increase in oil consumption; provided that the engine was initially in good condition.
• Similarly good results had followed the use of low-viscosity oils in petrol engines, the tests being conducted with a six.cylindered 3.52-litre unit which gave a nominal maximum output of 72 b.h.p. at 3.000 r.p.m. when running on S.A.E.30 oil.
Using S.A.E.I0w and 5w oils. improvements in corrected b.h.p. of the order of 2 per cent. at 3,000 r.p.m., with slightly higher percentage increases at lower speeds, were recorded. For a given power output, fuel economy of the order of 2 per cent, could be expected from low-viscosity oils.