See full version: A quick and dirty guide to gear oil
So a 75W-140 gear oil has similar performance to an SAE 75 gear oil while at 0°C. The single grade oils performance would only be measured at 100°C. Gear oils can get remarkably close to performing almost uniformly across the spectrum, with grading like 75W-85 gear oil being fairly common. more
ISO grades are internationally agreed upon standards for oils used in industry. ISO 68, for instance performs at 67.5cSt at 40°C. ISO grades tend to be much easier to read, since they’re tied to the centistokes of viscosity of a substance at 40°C. They’re not an exact measurement but they’re close. more
This doesn’t mean much to most end consumers, who’ll simply want to match off with their owner’s manual for the vehicle. more
Low viscosity oils, on the other hand, are best for high speed systems with lower load. They provide a thinner film and better cooling to match the higher speed of the gearbox in question. here
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There are gaskets under inspection plates, which leak occasionally if the plate has been removed and refitted badly. Some plates can be reached only by removing the gearbox, a task best left to a garage. Other plates are more easily reached. [links]
If it is too low, top up to the upper limit with the correct grade of oil — as specified in the car handbook.
If the drain plug has a washer, fit a new one. Replace the plug firmly, but do not overtighten it. here
A leak at the front end of the gearbox may come from damaged seals in either the engine or the gearbox, or a gasket between the gearbox and the clutch bell housing . Such a leak often drips from the bottom of the bell housing.
The oil seal where the speedometer cable enters the gearbox sometimes fails. Fit a new one (See Fitting a new speedometer cable ).
The lubrication is designed to prevent metal-to-metal contact, between teeth on gears , for example. The type of oil used depends partly on the type of gears the manufacturer has designed into the gearbox.
The original "bullet-shaped" units require 17.5 oz of OMC Type "C" lubricant in the lower gearcase. The "bullet-shaped" lower units were offered on 1962 - 1968 OMC/Evinrude/Johnson 14-ft and 16-ft boats with the "DU" sterndrive model prefix.
"Bullet drives" would also see OEM-duty behind OMC Chevy II 153 (110 - 120 hp) fours (CU). The OMC V-4 (DU) was last offered in 1968 and was replaced starting in1968 with the Ford (UK) cross flow "Kent" OHV fours of 80 and 90 hp (NU) through 1971.
OMC Electric-shift Stringer Precautions:
OMC stern drives were usually painted white and had a large circular rubber surround seal or boot in the transom, although later (post-1968) a rectangular boot was used. The single transom mounting ring or boot accommodates all cooling, exhaust, control and steering elements, meaning no other through-transom openings were required (very unusual for the early sixties). Propellers were pin drive and the exhaust was not through the hub, but exited behind the propeller via a port that doubled as a cooling water inlet and adjustable rudder trim tab. The "Electric Stringers" are infrequently referred to as the "Model 14-family" of stern drives, probably named so for the introduction of their 14-inch diameter props.