JimMcNeely
New member
I have a 2004 30' with twin Merc 5.7L Carb'd w/B2 drives.
Last spring I installed a custom alarm panel that shows which engine is alarming and also has alarms for the bilges. The input circuit for the engine alarms circuit draws about 35 milli amps when the alarm is sounding this is the same as the original Merc alarm buzzers.
I have been getting a intermittant alarm on one engine at about 3200 - 3300 RPM after running for three or four miles. If I come down to a slower speed or speed up I do not get the alarm.
My engine temp gauges remain steady at 175 +/- a few degrees.
My engine oil pressures runs between 40 to 55 depending on RPM.
My drive lube is full.
Engine temps measured with an IR gauge are virtually identical between the engines.
There is a single wire sensor on the thermostat housing. If I pull the wire the helm temp gauge falls to the stop.
I unplugged what I understand to be the overtemp sensor (two wires on the port side of the thermostat housing) the alarm did not re-occur. So I purchased a replacement overtemp sensor. With the new sensor I still get an alarm.
At my wifes urging I disconnected the alarm panel and reinstalled the original buzzers. I made sure the overtemp was reconnected and the alarm did not reoccur.
This got me looking at the sensors why would one system trip and the other not ?
My understanding was that the overtemp , oil pressure and drive lube are all on/off switches. But when I test the overtemp sensor it is a variable resistance 2400 ohms at 70F and about 400 ohms at 160F. This I do not understand.
The Merc circuit diagram shows the alarm which is connected to 12V when the key is on , the three sensors in parallel are potential paths to negative which can cause the alarm to sound when they complete the circuit.
So here is the point.
So why would one alarm system alarm sound and the other not when the control is simply a on/off circuit and the impedence of the two alarm systems is virtually identical ?
Why is the sensor a variable resistance and not on/off ?
Am I looking at the wrong sensor ?
Am I misunderstanding the circuit ?
I would like to disconnect and test each sensor but I am not sure about the overtemp sensor and I really do not know where the oil sensor for the alarm is at. Is the oil sensor for the alarm the single wire sensor on the Stbd side of the engine block below the exhaust manifold about center front to back ?
I am sorry for so many questions and I appreciate your help.
Jim
Last spring I installed a custom alarm panel that shows which engine is alarming and also has alarms for the bilges. The input circuit for the engine alarms circuit draws about 35 milli amps when the alarm is sounding this is the same as the original Merc alarm buzzers.
I have been getting a intermittant alarm on one engine at about 3200 - 3300 RPM after running for three or four miles. If I come down to a slower speed or speed up I do not get the alarm.
My engine temp gauges remain steady at 175 +/- a few degrees.
My engine oil pressures runs between 40 to 55 depending on RPM.
My drive lube is full.
Engine temps measured with an IR gauge are virtually identical between the engines.
There is a single wire sensor on the thermostat housing. If I pull the wire the helm temp gauge falls to the stop.
I unplugged what I understand to be the overtemp sensor (two wires on the port side of the thermostat housing) the alarm did not re-occur. So I purchased a replacement overtemp sensor. With the new sensor I still get an alarm.
At my wifes urging I disconnected the alarm panel and reinstalled the original buzzers. I made sure the overtemp was reconnected and the alarm did not reoccur.
This got me looking at the sensors why would one system trip and the other not ?
My understanding was that the overtemp , oil pressure and drive lube are all on/off switches. But when I test the overtemp sensor it is a variable resistance 2400 ohms at 70F and about 400 ohms at 160F. This I do not understand.
The Merc circuit diagram shows the alarm which is connected to 12V when the key is on , the three sensors in parallel are potential paths to negative which can cause the alarm to sound when they complete the circuit.
So here is the point.
So why would one alarm system alarm sound and the other not when the control is simply a on/off circuit and the impedence of the two alarm systems is virtually identical ?
Why is the sensor a variable resistance and not on/off ?
Am I looking at the wrong sensor ?
Am I misunderstanding the circuit ?
I would like to disconnect and test each sensor but I am not sure about the overtemp sensor and I really do not know where the oil sensor for the alarm is at. Is the oil sensor for the alarm the single wire sensor on the Stbd side of the engine block below the exhaust manifold about center front to back ?
I am sorry for so many questions and I appreciate your help.
Jim