posted 09-26-2007 05:50 AM ET (US)            

CONTINUOUS BEEEEEEEEEEP ALARM = overheat condition

BEEP BEEP BEEP ALARM = oil system problem

OIL SYSTEM PROBLEM DIAGNOSIS

In the oil system there are two sensors which monitor the oil system. One sensor detects the level of oil in a reservoir tank. The other sensor monitors the operation of the drive shaft of the oil mixing bump. If either of these sensors detect a problem, the same alarm signal cadence is produced. Therefore the alarm signal is now ambiguous. In order to resolve the ambiguity of the alarm signal, the operator must investigate the problem. Let us explore this problem solving.

RESOLUTION OF AMBIGUITY IN MERCURY OIL ALARM

If a Mercury engine sounds an alarm with a cadence of BEEP BEEP BEEP, it is indicative of a problem in the oil system. There are several conditions which could have produced the alarm. At the first level of investigation there is an assumption made that the alarm signal is a valid alarm condition. Proceeding on that basis, the alarm could be caused by two conditions:

--OIL RESERVOIR LEVEL LOW
--OIL MIXING PUMP MOTION FAILURE

To determine which condition is present, the operator must remove the cowling from the engine and observe the level of oil in the reservoir. If the level of oil in the reservoir is low, this condition is assumed to have caused the alarm. The remedy for this problem is to locate the cause of the low oil level in the reservoir tank. There are several possible causes:

DIAGNOSIS OF LOW OIL RESERVOIR LEVEL

If a low level of oil is seen in the under-cowling reservoir, the cause of this could be due to:

--low oil level in the upstream tank which feeds the reservoir; the oil system has run out of oil and needs to be replenished;
--failure of the oil system to pump oil from the upstream tank to the reservoir; the oil system has sufficient oil but it is not being pumped from the main tank to the under-cowling reservoir
--failure of the reservoir tank to maintain oil; the tank has a leak

In either case the next step is to examine the level of oil in the main oil tank. Observation of this oil tank level will help to further deduce the problem. There are two possible situations:

--the main oil tank has been emptied of oil
--the main oil tank has not been emptied of oil

If the main oil tank is empty, the oil system is about to run out of oil. The remedy is for the operator to add oil to the main oil tank, add oil to the under-cowling reservoir tank, bleed air from the oil system, and resume operation. This should terminate the alarm condition.

If the main oil tank is not empty, this is indicative of a problem in the transfer of oil from the main tank to the under-cowling reservoir. The operator must investigate this system further to determine the cause of the problem. There are several possible causes:

--loss of pressure in the main oil tank
--leak in oil hose delivering oil from main tank to reservoir tank
--leak in the reservoir tank
--obstruction in flow between main and reservoir tank

A loss of pressure in the main tank can be caused by several failures. The most likely failure is a loose cap on the tank or a failure of the tank-cap seal. The main tank must be sealed and maintained at a higher pressure than atmospheric pressure. Inspect the cap and its seal. A loss of pressure can also be due to a failure in the pressurizing system. Check the hose which pressurizes the tank and its connection to the tank. A loss of pressure could also be due to the special check valve and regulator which accumulates engine crankcase pressure pulses.

A leak in the oil hose between the main tank and the under-cowling reservoir can also cause failure of oil to transfer between the two. Inspect the hose. A leak should be fairly easy to locate due to flow of oil from the hose.

A leak in the reservoir tank can also cause a low level in the reservoir tank. Inspect the reservoir tank for indications of a leak.

Failure to transfer oil between tanks can also be due to an obstruction in the hose between tanks. In some installations there may be an in-line oil filter which can become blocked

DIAGNOSIS OF OIL PUMP MOTION FAILURE

If the oil tank levels are normal, the operator must then proceed to resolve the ambiguity of an oil alarm by assuming there has been a failure in the oil mixing pump motion. The oil mixing pump is a mechanical pump whose motion is driven by a shaft. The drive shaft is driven by a gear which engages a matching gear on the engine crankshaft. The crankshaft gear is a steel gear. The drive shaft gear is made of plastic. The most likely cause of lack of motion in the oil pump is failure of the plastic drive gear.

The tear down and inspection of the oil pump drive system is typically beyond the level of problem solving performed by an operator. At this point the operator should stop operation of the engine on regular gasoline fuel and switch to a fuel which contains oil and gasoline pre-mixed in the proper ratio, normally 1:50. This will not stop the alarm from sounding, however, but the engine will be able to be run so that the boat can be moved to a repair facility. Once the boat is at a repair facility, the oil mixing pump can be torn down and inspected.

INVALID ALARM

If investigation of the oil system as described above does not produce a clear indication of a failure, or if remedy of any of the above conditions does not produce an end to the alarm condition, the operator must investigate further. There are at least two possible causes:

--there are multiple problems causing the alarm; although one problem has been remedied, there is a second problem which is still signaling an alarm
--there is no actual alarm; the alarm system has failed and is signaling a false alarm

If the persistent alarm is due to another actual problem, return to the diagnosis procedure above and look for the cause. If the persistent alarm is due to a failure in the alarm system, check the alarm system

DIAGNOSIS OF ALARM SYSTEM MALFUNCTION

The alarm system may produce an aural alarm signal when no valid alarm condition exists. The alarm system is electrical in nature. To diagnose an alarm system malfunction, the operator has to investigate the electrical inputs to the alarm system. If the electrical inputs to the alarm system are valid, but the system is producing an alarm, then the likely cause is a failure of the alarm system.

ELECTRICAL INPUTS TO ALARM SYSTEM

There are six electrical inputs to the alarm system which should be checked to verify they have proper input signals:

--electrical ground or battery negative
--positive 12-volts or battery positive
--input from float switch in oil reservoir tank
--input from thermostatic switch in cylinder head
--input from motion detector in oil mixing pump
--input of a tachometer signal (which is used to provide a comparison for the mixing pump signal)

The electrical power inputs, battery positive and negative, are easily checked with a voltmeter. The two switch inputs can be disconnected and checked for continuity or open circuit conditions with a continuity tester or ohmmeter. The input from the motion detector is more difficult to assess. (Advice is needed on how to assess the electrical condition of the input from the motion sensor. If readers have knowledge of how to perform this assessment, please advise the author.) Input of the tachometer signal is also difficult to assess with a simple voltmeter. (Again, advice is sought on how to assess this signal.)

posted 09-26-2007 06:07 AM ET (US)            

The conditions described in the owner's narrative of the Mercury outboard motor alarm are unusual. The pattern of the aural alarm is not consistent with the either of the two cadences of alarm signal which are described in the Mercury literature. According to the owner's manual (as described by the owner above), the aural alarm signal is possible only in two distinct cadences:

--CONTINUOUS BEEEEEEEEP
--BEEP BEEP BEEP (repeating)

Yet the owner describes a third cadence, a sporadic and intermittent single BEEP. Such an alarm cadence is not described in the owner's manual.