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Author Topic:   Smartcraft Gauge
chiefrob posted 04-30-2010 07:43 PM ET (US)   Profile for chiefrob   Send Email to chiefrob  
[I believe this author is trying to convey to us that he has some sort of problem with a Mercury Smartcraft] gauge [that is somehow associated with an] engine-mounted oil reservoir tank running low on oil. [The engine-mounted oil reservoir tank] is full, as is the main engine oil tank. Everything else is fine.
jimh posted 04-30-2010 08:53 PM ET (US)     Profile for jimh  Send Email to jimh     
I am sorry to say that I am at a complete loss to understand the nature of the problem. Please try to explain the problem more precisely. I think you can get some advice on resolving the problem, if we can understand exactly what is malfunctioning.
chiefrob posted 05-01-2010 05:27 AM ET (US)     Profile for chiefrob  Send Email to chiefrob     
Sorry for the lack of detail in original post. My smart craft gauge signals, through a series of beeps, that my engine mounted oil reservoir tank is running low on oil. As stated, that tank and the main oil tank under the deck, have plenty of oil. I took the engine mounted tank off to unscrew and check the probe which is connected to a wire that runs under the engine. I thought it may be a float that was hung up and sending the wrong signal to the smart gauge module. It is not, rather it is an enclosed piston type probe with no apparent float. I am wondering if this "probe" is the issue and has to be replaced. I am sorry for the lack of technical acumen.
jimh posted 05-01-2010 12:15 PM ET (US)     Profile for jimh  Send Email to jimh     
Thanks for the further information.

I am not precisely familiar with the under-cowling oil reservoir in your Mercury motor, but the general arrangement of the tank level sensor used by Mercury in the past has been to employ a magnetically operated switch to sense the oil reservoir level. There typically is a float in the oil reservoir which has a magnet attached. The float moves with the oil level, and when the oil level in the reservoir falls, the float moves away from the magnetic switch, triggering an alarm.

Assuming your system works in this same way, there are several possible causes for a false alarm that indicates the oil level is too low when in fact it is not. I list them in the order in which I suspect most likely to occur:

--the magnet has become separate from the float

--the float has lost buoyancy and has sunk

--the magnetic switch has malfunctioned

--there is a wiring problem in a connector or in the switch circuit

--the magnet, float, switch, and wiring are intact and there is a problem in the alarm module that interfaces to them.

jimh posted 05-01-2010 12:43 PM ET (US)     Profile for jimh  Send Email to jimh     
I am sorry--I did not carefully read your narrative where you exclude the level sensor from being based on a float or on some basis of buoyancy of the sensor in the oil.

I am not familiar with the design of the level sensor used by Mercury for the under-cowling oil reservoir tank as you describe, but we can apply some of the same logic to diagnosis of the problem of the false alarm.

We have an alarm indicating low-oil level but we see visually the oil level is fine. This implies a false alarm. The likely causes of a false alarm are:

--bad sensor

--bad wiring between sensor and alarm module

--bad alarm module

You should first investigate the sensor. Perhaps you can deduce the principle of its operation from inspection of the device. If there is not floatation or buoyancy involved in sensing of the tank level, the operation of the sensor must be based on some other method. One method of detection of oil level might be to immerse two electrical contacts in the oil and monitor for a change in resistance between them. This method does not seem likely, as most oils are not very good conductors of electricity, and the change in resistance (from oil to air) would be hard to detect. Another basis for a sensor might be optical. The sensor reacts to a change in the transmission of light between a source of light and a sensor of light. But this also seems unlikely, as oil is known to cling to surfaces and could make reliable detection of a level drop difficult. This brings us back to buoyancy as being the most common sensor technique with regard to tank level indicators.

I am sorry to say I am not familiar with this level indictor, but I would very much like to learn about it. If you discover the basis on how it detects tank level, please let us know.

To test the sensor you might be able to monitor its electrical properties while changing the sensor input to correspond to different tank levels. You should observe a change in the electrical properties of the sensor. Typically the OEM service manual for your Mercury engine will include a procedure for testing the sensor to establish if it is operating properly.

chiefrob posted 05-01-2010 05:41 PM ET (US)     Profile for chiefrob  Send Email to chiefrob     
I cut the wires to the sensor, and while on the water,Smart Craft Alarm engaged and the engine throttled back. Came home and cut (two)wires to sensor. Engine ran fine all the way up to 3500 to 4000 rpms. I stripped and tied wires together to create a closed circuit. The sensor to the accessory oil tank on the engine has been bypassed pending further investigation and repair. Thanks for all your help. I will post ultimate findings once I get it repaired.

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