Campbell Boat Owners Website

Motor Oil

Article by Campbell Boat Owner Ron Fasola, owner of "Strange Brew"

In November 2004, a rather unique situation took place in that when the API, (American Petroleum Institute), came out with their latest motor oil rating designation of SM for 2005 and newer engines, there was controversy. The API service rating is always shown on the API "Service Symbol Donut" along with a motor oil's viscosity in the familiar circular ring on the oil container. In the past, each time the API came out with a new designation, (old obsolete designations include SH, SG, SF, SE, etc.), the oil meeting the new designation was "better" in some way. The new spec had better performance regarding either anti-wear additives, oxidation stability, foaming control, detergency, etc. SOMETHING was better, or there wouldn't really be a need for a later API designation. Also, it was always the case that the new designation was "backwards compatible", meaning the newer designated oil could always be safely used in older motors. The opposite was not true, however; older obsolete service classifications may not meet the lubrication requirements for newer engines.

The problem is that the new SM designation has much lower levels of anti-wear additive, or zinc Dialkyl Dithio Phosphate, (ZDDP), than the older designation it replaced, because it was designed to accommodate late model, (2005 and newer), engines and their systems. SM oils are down to 0.08% ZDDP. There are two reasons for this.

1.      These late model motors all have roller lifters, some have roller rockers, some have roller everything. Rolling contact is much easier on the lubricant than flat tappet camshafts, (like the cams in most of our older marine engines). So there is less need for the prior high levels, (0.12%), of anti-wear in the new SM oil.

2.      ZDDP shortens the life of catalytic converters, so this was another huge reason to reduce its levels in motor oils.

For 2005 and newer automotive engines, the lower levels of ZDDP do not present a problem. But for us boaters with older pushrod motors, the problem is major. The interface between a camshaft lobe and a lifter is the highest pressure mating surface junction in an engine. It gets even worse for high performance engines that have higher lift cam profiles, (sharper ramps), and stronger valve springs to prevent valve floating and allow higher rpm service. Then there's the fact that marine engines work way harder in their environment than automotive engines. Boat motors are subject to much greater loads and higher rpm operation, which make the demands on boat motor oil much tougher.

The bottom line here is that SM oils are NOT the oil to use in older boat motors; higher levels of ZDDP are needed. Racing oils do not have to meet OEM specs, and typically have the higher levels of ZDDP needed. There are a variety of racing oils in various viscosities available, and their specs, which include their zinc content, can be researched on the internet. Racing oils are usually intended for race engines, (duh!), and race motors get their oil changed usually each race. Therefore, race oils are usually a little shy on the amount of detergency they contain because there's not much need for detergency in a race motor that gets constant oil changes and gets rebuilt frequently. So if race oil is used in a boat motor, it would be a logical idea to shorten up the oil change frequency just because of the lower detergency factor.

RELATED NOTES

         If your motor was not specifically built with bigger than stock clearances, don't waste horsepower and impose poor cold oil temp lubrication by using high viscosity lube oils like straight 50W. There's no good reason for increased clearances anyway. 90 psi oil pressure is a waste.

         50W oil, being more viscous or "thicker", can indeed reduce oil consumption in a worn out motor. It's rather like adding sawdust to a gearbox to quiet it down. When increased clearances result from wear, high vis oils can be a band aid method of controlling high oil consumption. However, it is assumed you know that the real solution to a worn engine is a rebuild or a replacement.

         Synthetic oils have their place, but with a few exceptional applications, they are usually not worth their price. They have great oxidation stability, (i.e. they can withstand higher temperatures than conventional oils can), so if your boat does not have an oil cooler and/or your motor oil in the summer typically runs at oil temps over 220 degrees F, then synthetics might be for you. Synthetic oils' cold temp properties are truly wonderful, but not needed for most boating applications, (unless you boat in Alaska).

         Multi-viscosity oils like 10W-30, are generally not a bad idea for boat motors because typically, a boat is idled off the trailer and gets hit rather hard shortly thereafter to get on plane. Some boaters get on plane and immediately run right up to a high rate of speed, which is tough on a cold motor with cold oil. The first number, the "10", in 10w-30 or 10W-40 will help in these situations because the low temp property of the lube oil meets 10 "weight" spec, and flows more easily to critical engine parts when cold. Be aware, however, that the greater the viscosity spread, like 10W-40 and 20W-50, the more "VI" (viscosity improver) additives are used. This is not a good thing, because the more VI in the oil, the higher the tendency for the oil to "shear down" to lower viscosity under high heat or high shear. A 20W-30 can quickly become a 10W-20. There is more sludging with multi vis oils also. So if you tend to run consistently at high, (over 220 F), oil temps, straight grades may be better for you; but take it easy on the motor until it's warmed up a little.