Automatic Oiling System: OMC/Bombardier versus Mercury

Two previous articles described the automatic oiling system used in the outboard motors manufactured by OMC/Bombardier for their Evinrude and Johnson brand engines and by Mercury Marine for their Mercury brand engines. This article compares the two systems. It points out areas where they are similar or different in the methods and techniques used to accomplish this function. Observers have often asserted that one oiling system is superior to the other. This article will examine the systems in detail and show where they are alike and where they differ. Observations will be made of the benefits and advantages of various techniques encountered.

Automatic Oiling Systems

The automatic oiling system of an outboard motor stores two-stroke lubricating oil in a reservoir or tank, pumps the oil to the engine, and mixes it with the gasoline in the proper ratio. The operation of the system is monitored by sensors which can trigger alarms if a malfunction occurs.

Components of Automatic Oiling Systems


OMC pioneered the use of automatic oiling systems with their "VRO" or "variable ratio oiling" system introduced in c.1984. Two years later they improved the system and called it "VRO2". In 1993 the oiling system was further improved and called the "OMS" or "oil metering system". It is common for all three of these system to be referred to as simply "VRO" systems. The description herein refers to elements common to all three systems, unless specifically mentioning a particular variation.

The OMC oiling system uses a single reservoir tank located remote from the motor. Oil is drawn by suction from the tank by a lift pump and delivered to the engine, where it is mixed with the gasoline. Three sensors monitor for problems and provide distinctive alarm signals.


Mercury followed OMC's lead in the 1980's and began to offer an oil mixing system of their own. Historical information is not known at this writing. There does not appear to be a particular model name used to describe the system.

The Mercury oiling system uses two tanks: a remote tank feeds an under-cowling reservoir. Oil is pumped under pressure from the remote tank to the reservoir. The reservoir feeds by gravity to a mixing pump. Two sensors monitor for problems and trigger a common alarm signal.

Executive Summary

The two oiling systems have been around for a while. They use surprisingly similar techniques for some parts. The biggest difference is the way their mixing pump is driven: OMC/Bombardier uses an air motor; Mercury uses a plastic gear. OMC/Bombardier has more and better alarms. Who's the best? Read on for more details.


The four main components of the systems will be described in detail: reservoir, transfer pump, mixing pump, and alarm system.


Both systems employ a remote oil reservoir with a capacity of 1.8 to 3 gallons. The OMC/Bombardier tank is available in two sizes, permitting the oil reservoir capacity to be matched to the engine consumption rate. The tanks are molded plastic and have two openings. Each has removable threaded plastic caps to facilitate adding oil. The cap and opening on the Mercury tank is larger than the cap and opening on the OMC/Bombardier tan, although both are suitable for the purpose of adding oil. The OMC/Bombardier tanks have a fixed fitting for admitting a hose connection. The fitting is mounted to the top surface of the tank and sealed with a gasket. Mercury tanks also have a second opening, but it is another threaded cap-type opening. Fittings for admitting hoses to the Mercury tank attach to a quick-disconnect fitting on the cap assembly which threads onto the opening.

Both the OMC/Bombardier and Mercury remote tanks have a pick-up tube which extends to the bottom of the tank to withdraw oil. The OMC/Bombardier pick-up orifice is fitted with a replaceable fine mesh screen to provide a filter. The Mercury pick-up tube has a filter, but the details of it are not known.

The OMC/Bombardier remote oil tank also contains a float mechanism which provides an electrical contact closure when the level in the tank falls below about 1/4-full. The float mechanism is not associated with the cap and is not withdrawn when the cap is removed. There is no float level or electrical contact in the Mercury remote tank.

Mercury employs a second oil reservoir located under the engine cowling which has a capacity of approximately one liter, and can provide oil for about 30-minutes of engine operation after the remote tank is emptied. This tank has an inlet fitting at its top which receives oil pumped from the remote tank. The tank has a threaded opening on the top to which a cap is installed. The cap has an attached float mechanism which provides an electrical contact closure when the level in the reservoir falls below about 7/8-full. An outlet at the bottom of the reservoir permits oil to flow to the oil mixing pump

The single removable cap of the OMC/Bombardier remote oil tank seals the tank but provides a baffled venting of the tank to the atmosphere. To fill the reservoir, the cap is unscrewed and oil is added. A small chain is attached to retain the cap, but there are no hoses or pick-up tubes attached to the cap. The filler cap of the Mercury remote oil tank is similar device, but the opening in the tank is larger. All caps in the Mercury oiling system are designed to seal air-tight, even the caps which contain pass-through fittings for oil or electrical connections.

A comparison of the tanks finds the following differences:

Oil Transfer Pump

It is practically universal that the remote oil tank is located below the level of the engine power head. Thus oil must be lifted from the remote tank and delivered to the power head. This function is provided by the oil transfer pump or oil lift pump. Here we will consider the transfer pump as a system which includes all of the components from the remote oil tank up to the inlet of the next stage of the system, the mixing pump.

In both the OMC/Bombardier and Mercury oiling systems, the energy to power the oil transfer pump is obtained from the mechanical energy available in the outboard motor when running. In both cases, the energy is derived by extracting either pressure or vacuum pulses from the crankcase of the engine. In the OMC/Bombardier system, an "air motor" converts crankcase pressure and vacuum pulses into mechanical movement which operates a diaphragm pump. In the Mercury system, crankcase pressure pulses are accumulated and regulated by a check valve and applied directly to the remote tank via a hose, pressurizing the tank.

In both cases, the fluid oil is pumped from the remote tank to the engine by establishing a pressure differential between the two ends of the system. Because liquids such as oil cannot be compressed, application of pressure to them tends to cause them to flow from high-pressure areas toward low-pressure areas. The principal difference between the two implementations is the use the pressure in the system relative to atmospheric pressure.

The OMC/Bombardier system maintains the pressure at the supply end of the system and throughout the connecting hoses at atmospheric pressure, and it lowers the pressure at the delivery end of the system to below atmospheric pressure. This differential in pressure causes the oil to flow from the tank and be lifted to the engine power head for delivery to the mixing pump. When the pressure differential is lost, oil flow stops.

The Mercury system forces the pressure at the supply end of the system and throughout the connecting hoses above atmospheric pressure, and it maintains the pressure at the delivery end at or near atmospheric pressure. This differential in pressure causes the oil to flow from the remote oil tank and be lifted to the engine power head for delivery to the under-cowling oil reservoir. The under-cowling reservoir is also maintained above atmospheric pressure, and oil flows from the reservoir via an outlet on the bottom for delivery to the mixing pump. When pressure differential is lost, oil from the remote tank stops flowing to the under-cowling reservoir, however oil in the reservoir will continue to flow to the mixing pump due to gravity, as the mixing pump is located below the level of the reservoir tank.

Although the two systems use a differential in pressure to produce flow, they differ slightly in the approach. Most of the OMC/Bombardier system is operating at atmospheric pressure, while most of the Mercury system is operating above atmospheric pressure. In order for either systems to operate, all connections between the oil tanks and the mixing pump must be maintained as both air tight and oil-tight. The effect of any failure in the connecting hoses of either system will result in an eventual failure of the transfer pump to deliver oil from the remote tank to the power head. We examine in more detail.

In order for the transfer pump of the OMC/Bombardier system to develop a pressure differential between the remote oil tank and the pump inlet, all of the connecting hoses, clamps, and connections between them must be maintained with air-tight integrity. If a leak occurs, air will tend to be drawn into the system. The rate at which air will be drawn into the system will be proportional to the size of the opening of the leak and the pressure differential at that point.

In order for the transfer pump of the Mercury system to develop a pressure differential between the remote oil tank and the pump inlet, all of the connecting hoses, clamps, connections, and intermediate reservoir tanks between them must be maintained with air-tight integrity. If a leak occurs, oil will tend to be forced from the system. The rate of flow of oil from the system will be in proportion to the size of the opening of the leak and the pressure differential at that point. A small pin-hole leak in a hose may cause a nozzle effect and produce a spray of oil.

Both pumping systems require "priming" before operation can begin. Air must be evacuated from the system for proper operation of the transfer pump.

The OMC/Bombardier oil system locates the transfer pump at the delivery end of the system (i.e., the output of the transfer pump is delivered immediately to the mixing pump, as the two are part of the same assembly), and thus it requires priming of the INLET side of the transfer pump to purge air. A priming bulb in the connecting hose between the remote oil tank and the transfer pump inlet provides priming. Temporary removal of the supply hose at the transfer pump inlet and operation of the primer bulb result in very effective priming and purging of the hose system between the tank and pump inlet for initial installation. Once primed, the system will retain prime as long as the hose between the pump inlet and the oil tank pick-up remain air-tight and supplied with oil. A sight gauge in the oil line near the inlet of the transfer pimp confirms the system has been primed.

The Mercury oil system locates the transfer pump on the supply end of the system (i.e., the remote tank itself), and thus it requires priming of the OUTLET side of the transfer pump system to purge it of air. The outlet hose can be primed by first manual filling the under-cowling reservoir. Oil will flow by gravity to the outlet of the reservoir. A bleed screw facilitates priming. The outlet hose connection to the next stage (mixing pump) must be loosened temporarily to bleed any air entrapped in the line. Gravity will maintain the prime between the under-cowling reservoir and the mixing pump for indefinite periods, as long as the reservoir supplies oil. With the under-cowling reservoir near full, the system can be temporarily operated with the normally air-tight cap ajar, permitting the remote tank to purge the supply line between remote tank and reservoir of any air. When the connecting hose is purged of air from pumping of oil through the hose, the cap can be tightened.

A comparison of the oil transfer pumps finds many similarities. The principal difference is the location of high and low pressure areas in the system, relative to atmospheric pressure. Both require initial purging in which it may be necessary to temporarily loosen hose connections to obtain proper priming. Both require that the connecting hoses, fittings, and clamps remain air-tight for proper operation. Both use rubber hoses as a conduit for the oil, plastic fittings, and appropriate cable clamps.

A list of the components, connections, and fittings in each system will be illustrative of the differences by which they implement their oil transfer pump system:

The transfer pump system in the Mercury implementation has more components than the OMC/Bombardier implementation. All of these additional components are associated with the under-cowling reservoir tank. Otherwise the two systems are very similar.

Mixing Pump

After oil has been pumped from the remote oil tank to the power head by the oil transfer pump, a mixing pump dispenses oil in proportion to the gasoline being used. This is the essential feature of any oiling system: the oil and gasoline be automatically mixed at a suitable ratio, relieving the operator of having to accomplish this by manual pre-mixing in the fuel tank. The ratio of oil to gasoline is also varied proportional to engine speed. At lower engine speeds the mixing pump output is controlled so as to maintain the ratio of oil to gasoline around 1:100, and as the engine speed increases, the output of the pump increases at a faster rate than the gasoline flow increases so that the ratio of oil to gasoline is varied until it increases to around 1:50. This provides the engine with more lubricating oil as its speed increases. At low speeds the engine can operate with less lubricating oil, and this produces two benefits: less consumption of oil and less smoke in the exhaust. This is the essential feature of a variable-ratio automatic oiling system. All of this is accomplished in the mixing pump. There are considerable difference between the OMC/Bombardier and Mercury implementations of this important function.

The mixing pump requires a source of energy to operate. Both implementations develop mechanical energy from the outboard motor when it is operating. The methods are quite different and require further explanation.

Energy to operate the mixing pump in the OMC/Bombardier system comes from engine crankcase vacuum and pressure pulses. In fact, the same air motor system which drives the oil transfer pump also drives the oil mixing pump (as well as the fuel pump, to be explained later). Indeed, the OMC/Bombardier oil mixing pump is simply another chamber in the assembly that also includes the oil transfer or oil lift pump, as well as the fuel pump.

The Mercury mixing pump is an entirely separate pump which is driven by mechanical gearing operated directly from the crankshaft of the engine. A plastic drive gear on a crankshaft journal rotates at crankcase speed (i.e, up to 6,000-RPM). The plastic drive gear engages a steel long spline driven gear from the mixing pump which extends into the engine block to reach the plastic drive gear.

Now we turn to the actual mixing pump itself. Unfortunately the details of the Mercury pump are not as well-known as those of the Bombardier pump. No exploded view of the pump itself is available.


In the OMC/Bombardier implementation of automatic oiling, the mixing pump is essentially the same pump as the transfer pump. That is, a single pump provides both functions, as well as being linked internally to the same air motor driving the fuel lift pump. (Note: if the air motor fails, both the fuel and oil pumps will stop. Thus you cannot get delivery of fuel without oil as a result of an air motor failure.) For a view of the construction of the pump itself, see the separate article which describes it in detail.

The variable ratio mixing action is accomplished by the action of the crankcase pulses. As the engine crankcase speed increases, the frequency of the pulses increases as well. However, as crankcase speed increases, the pressure of the pulses increases, too, resulting in greater mechanical movement. This is translated into greater volume output from the oil pump, and, as a result, the mixture ratio increases to about 1:50 from 1:100 as the engine speed increases. The precise mixing ratios vary with different models of the pump. The current OMS version (after about 1993) averages a 1:60 ratio, going slightly leaner at idle and slightly richer at high speeds. A VRO2 version made about 1990 to 1992 used a 1:100 lean ratio. Earlier VRO2 and VRO versions (prior to 1990) used an even leaner 1:150 oil ratio at low speeds. All of these pumps made prior to 1993 would enrichen the oil to 1:50 at higher speeds. There is no adjustment available for altering the mixing characteristics of the pump, short of obtaining a different model of pump.

Because the mixing pump is part of the fuel pump assembly, the output flow of oil from the mixing pump is conveyed directly to the fuel pump chamber, and the two streams mix together and are sent to the fuel induction system.


The Mercury oil mixing pump receives oil by hose by gravity or pressure flow from the under-cowling reservoir tank. The rate of pumping is a function of crankcase speed and the position of a control lever which is mechanically linked to the throttle position. As engine speed increase, the pump is driven faster by its geared input shaft, producing more flow. As the throttle position is advanced toward full throttle, a mechanical linkage from the throttle actuator advances a control valve. The output of the pump is thus further increased so as to increase the mixing ratio. The ratio of oil to fuel obtained is specified to be about 1:100 at idle and increases to around 1:50 at wide-open throttle. Adjustment of the linkage and actuator using embossed calibration marks permit proper setting of the pump output to achieve the correct ratio. A bleed screw is provided for priming of the pump and purging of air.

The Mercury mixing pump is believed to be made by Japanese manufacturer Mikuni/Kehin. It has an unusual arrangement in which a moveable cylinder is operated by a cam that varies its stroke over a fixed piston.

The output of the pump is a flow of oil which is connected by hose to a one-way check-valve which connects via a T-fitting with the gasoline fuel line. Thus oil can flow into the fuel system, but fuel cannot flow back into the oil system. The oil joins the fuel system on the suction side of the fuel pump. This further helps to direct the flow of oil and fuel to the proper destinations at the mixing point. The fuel pump delivers the mixture of fuel and oil to the fuel induction system.

In comparison, the two systems are substantially different in their implementation of the mixing pump. The Mercury mixing pump is entirely separate from the oil transfer and fuel pumps, uses a gear drive, and links mechanically to the throttle for control of ratio. The OMC/Bombardier pump is integral to the oil transfer and fuel pump, is driven by the same air motor as the fuel pump, and automatically increases oil flow output with engine speed increase in a non-adjustable ratio built into the pump itself.

Alarm Sensors and System

Operation of the oiling system is crucial to engine operation. Most two-stroke engines will not tolerate operation without lubricating oil being supplied, and great harm can result if the oiling system fails. Accordingly, sensors and alarms are included to detect conditions likely to cause failure of operation of the system. The sensors are typically either level or flow sensors. The alarms are typically audible warnings.

The OMC/Bombardier oil system has evolved over 22 years to include three alarm sensors related to the oil mixing and fuel system. The current OMS system was implemented c.1992 and monitors the following portions of the oiling and fuel system:

When these alarm signals occur, they are indicated by separate LED annunciators, and they also trigger a separate aural alarm. The aural alarm sounds a common warning tone for these three alarms. The alarm system also includes a cylinder head temperature sensor as well as another separate LED annunciator for that condition. This also sounds the same common alarm. This system is part of the OMC/Bombardier SystemCheck system of sensors, alarms, and indicators. The system also performs a self test at start, including testing all visual and aural alarm indicators by illumination or sounding.

The OMC/Bombardier oil system is the ONLY oiling system which has a "no flow" alarm sensor.

Earlier implementations of the OMC/Bombardier oiling system have less comprehensive sensors and alarm systems. All systems after c.1986 have had a flow sensor which compared flow rate to tachometer pulses; system on 1984 and 1985 motors did not, but can be upgraded. Systems without the LED annunciators (i.e., prior to c.1993) still provided a means to differentiate between alarm signals by the cadence of the alarm sounder. Even the oldest motors can be up-dated with new alarm sensors and alarm indicators at relatively modest cost.

The OMC/Bombardier system places the aural alarm and the visual alarm annunciator at the helm position. They will be in clear view and within hearing of the operator.

The Mercury oil system has two alarm sensors. The precise history of the alarm system is not known, but is believed to date back to at least c.1987:

The separate electronic module receives the signals from the two sensors, as well as from a cylinder head temperature sensor and the ignition module. It is presumed the electronic module compares the rate of signal pulses from the mixing pump drive shaft motion sensor with ignition pulses. If the ratio fall below a fixed threshold an alarm is sounded. The module provides a aural self-test-passed signal at start-up to verify functioning of the electronics and the alarm sounder (typically the MORSE CODE signal Dah-di-dit "D" or Dah-di-di-dit "B"). It sounds a built-in aural alarm to indicate an alarm signal. The cadence of the alarm is continuous for engine overhead. The alarm sounds a short BEEP-BEEP cadence to indicate a problem in the oiling system. Unfortunately this does not distinguish which sensor caused the alarm. This ambiguity is resolved by testing and troubleshooting the oil system. See the service manual for details.

There is no sensor in the Mercury alarm system which monitors oil flow or indicates a lack of oil flow.

The Mercury alarm system has no visual indicators. The aural indicator in located under the engine cowling. Its alarm cadence does not differentiate between the level sensor or the motion sensor alarm.

Summary of Description

The four major components of the automatic oiling systems used by OMC/Bombardier and Mercury have been described in detail. As best as can be determined, all of the above description is accurate and based on factual information. We now turn to some further comparisons and conclusions regarding the two oiling systems which may involve more judgement and analysis. A number of persistent rumors or allegations will be investigated and examined for potential truths.


Boaters often allege that one automatic oiling system is better than another, particularly in terms of reliability. Because failure of the automatic oiling system can cause very serious and expensive damage to an outboard motor, the reliability of an oiling system is paramount. Is there any inherent advatange to either system? We examine the major components to see if there is a significant difference between them which could justify a conclusion of superiority.

Remote Oil Tank: Water Contamination

Contamination of the oil contained in the remote oil tank with water is a problem which could cause serious engine damage. Based on the similar materials and construction of the tanks, it is reasonable to conclude there is no significant difference in the two tank designs as far as their ability to prevent water from entering as long as the caps are in place and properly sealed.

If the fill cap is not in place, both systems will continue to function. Due to its wider opening, the Mercury tank will be more at risk for water contamination. A loose cap in the Mercury system will cause a failure of the transfer pump. This will eventually result in an alarm signal from the float level in the under-cowling reservoir when the oil level drops. This should occur in a reasonably short period of time, if the engine is being operated. A loose cap condition will not be detected by the OMC/Bombardier alarm system, and the system will otherwise operate in a normal manner. Note that risk for intrusion of water is independent of the engine being operated, and most boats are only being operated a very small amount of the time.

The vent opening in the cap on the OMC/Bombardier tank is not believed to be likely to allow ingress of water to the tank under normal conditions, such as occasional exposure to spray, and thus it is not judged to place the oil tank at risk for water contamination. It is common for the remote oil tank to be installed in a way that protects it from direct exposure to rain or spray. In open boats it is common for the oil tank to be located inside another enclosure, such as a battery box.

Both tanks are subject to contamination of their oil from water condensing on the inside of the tank. Because the Mercury tank is supplied with warm air from the motor via its pulse hose, it may be at more risk for formation of condensed water on the inside of the tank because air in its tank will vary over a wider temperature range. This may not be a significant difference. Otherwise, both tanks are assumed to be at equal risk for contamination of the oil with water from condensation.

System Integrity

The two system employ similar components such as plastic fittings, rubber hoses, and plastic hose clamps, and these are judged to be of similar quality. There are more components, hoses, fittings, and connections in the Mercury system, and thus there are more opportunities for failures. A failure in a fitting or hose will cause different effects. Because most portions of the Mercury system are operated at an elevated pressure (relative to atmospheric pressure), a leak or failure will likely produce an outflow of oil. This often provides a strong visual indication of the failure. The OMC/Bombardier system is operated at atmospheric pressure or below, and a leak or failure may not produce an outflow of oil. Instead there may be an ingress of air into the system. This may not produce any visual indication of the failure.

The Mercury alarm system will not detect outflow of oil from the system until the loss of oil causes the under-cowling reservoir level to fall. If air enters the OMC/Bombardier oil system, it may reduce the flow of oil. The alarm system will detect loss of oil flow caused by any reason, and an alarm will sound.

The Mercury system requires two hoses between the remote oil tank and the motor. One hose is an oil supply, the other a pulse hose which pressurizes the remote oil tank. The OMC/Bombardier system uses a single hose. These remote hoses are at greatest risk for damage caused by exposure to ultraviolet light, water, or direct physical damage from vibration, contact, being stepped upon, etc.

The Mercury system operates with more components under elevated pressure. This may place its components under more stress. Both system require system integrity be maintained for proper operation.

System Priming

Both the OMC/Bombardier and Mercury oiling systems require priming before operation. The Mercury system can be primed by using a bleed screw on the mixing pump, and by loosening the fill cap on the under-cowling reservoir tank. The OMC/Bombardier system can be primed using its primer bulb. A sight tube insert in the supply hose allows confirmation of oil delivery to the OMS pump. Both systems will tolerate a small volume of air bubbles in the system, and will expel them through the fuel pump and fuel induction system (which is vented to the atmosphere).

The presence of a primer bulb does not constitute a defect or potential point of failure. A primer bulb functions exactly like the diaphragm fuel pump or oil pump found almost universally on outboard motors. It has a pump chamber with check valves on the inlet and outlet sides. The chamber has a rubber diaphragm which moves in and out, alternately squeezing and releasing, creating pressure or suction. In an engine driven pump, the movement of the diaphragm is caused by engine crankcase pressure being applied to one side. In a primer bulb, movement is caused by application of pressure to the bulb or diaphragm itself by a human hand. The pumping action they produce is otherwise similar. The excursion distance in the engine drive pump may be smaller, but the rate of movement is much higher, i.e., occurring in proportion to engine crankcase speed.

The one-way check valves found in a primer bulb are exactly like other one-way check valves. Such valves are used throughout the oiling system in both the OMC/Bombardier and Mercury implementations, and their presence is not a cause for alarm.

Both systems require proper priming for operation. Both provides suitable means to accomplish priming without significant trouble.

Alarm Systems

The OMC/Bombardier system is the only system which monitors for and detects a loss of oil flow. Both systems monitor for oil level in their tanks. The OMC/Bombardier alarm system monitor is better located at the helm position and provides a clear and unambiguous indication of the sensor triggering the alarm.

Pump Drive Mechanisms

Both OMC/Bombardier and Mercury use crankcase driven vacuum or pressure pulses to develop mechanical motion for operation of pumps. Mercury uses them for its fuel pump and oil transfer pump, but changes to a mechanical gear driven pump for its oil mixing pump. OMC/Bombardier use crankcase vacuum/pressure pumps for all three application, as all three functions are built into a single pump.

The significance of Mercury's choice of a gear driven pump for its mixing pump is not known with certainty. The plastic gears can be damaged if the engine overheats. Concern about their reliability caused a motion sensor and alarm to be added to the system. Replacement of the plastic drive gear requires substantial teardown of the engine.

Replacement Costs

The OMC/Bombardier oil transfer pump, oil mixing pump, fuel pump, crankcase pressure regulator and alarm system are contained in a single replacement kit which costs about $275 retail. Installation is straightforward, and can be done without special tools or engine tear down. Repair kits for the pump are also available and cost much less. They provide new internal components for the pump assembly which require tear down and reassembly of the pump itself.

The Mercury transfer pump is just a simple crankcase check valve, and is believed to be inexpensive. Cost of the mixing pump is estimated to be above $250. The cost of the electronics module for the alarm is believed to be about $250. Costs for replacement of the crankcase mounted plastic drive gear are low but labor costs would be substantial.

Costs for the plastic reservoir tanks, caps, and float sensors are believed to be moderate and comparable between the OMC/Bombardier and Mercury devices.

Replacement costs for the Mercury system appear to be higher. This may be mitigated by a greater durability and lack of rubber components subject to decay and replacement.

Anecdotal Reports

There are more anecdotal reports of problems with the older OMC oiling systems than there are for older Mercury systems. This may be due to problems related to a change in gasoline formulation which affected rubber components produced prior to c.1987. Some OMC oiling products pre-date this epoch, and may have suffered from the effects of alcohol-diluted gasoline on their rubber components. The Mercury oil mixing pump may not contain rubber components; its internal components are not in direct contact with gasoline. This may be related to a lower number of anecdotal reports of failure of older Mercury oiling systems.

There are no accurate or reliable data about the comparative rate of failure of the two systems. Such data are seldom available from the manufacturers. Recitations of particular statistics related to numbers of failures are considered unreliable, and are almost universally provided without any reference.

Anecdotal recitations of opinions expressed by others are simply that. First-hand accounts of failures of either the OMC/Bombardier system or the Mercury system are more credible but less often provided.

DISCLAIMER: This information is believed to be accurate but there is no guarantee. We do our best!

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Author: James W. Hebert
This article first appeared April 2, 2006.