fisherman
Well-Known Member
How can I test my engine overheat alarm? Siren sounds at switch on, but that's oil as well.
Test engine alarm?
- Thread starter fisherman
- Start date
rob2
Well-Known Member
When you switch on, the oil pressure alarm will sound because there is no pressure. Depending on the wiring of your panel there may also be an alarm as there is no charge current. The overheat alarm should not be sounding as the engine is cold.
Usually all the alarms share a return to earth through the siren, so you can't tell which is sounding it. If the sender type is suitable, you could disconnect the other alarms and play a blow torch over the temperature sensor - but I wonder if there is any risk to the sensor from such abuse?! Do you know what temperature it is supposed to sound at? It may be enough to dunk it in boiling water...
Rob.
Usually all the alarms share a return to earth through the siren, so you can't tell which is sounding it. If the sender type is suitable, you could disconnect the other alarms and play a blow torch over the temperature sensor - but I wonder if there is any risk to the sensor from such abuse?! Do you know what temperature it is supposed to sound at? It may be enough to dunk it in boiling water...
Rob.
fisherman
Well-Known Member
I think it will have to be boiling water, was hoping for some way to avoid removal.
rob2
Well-Known Member
Sadly to test in situ you'd have to forcibly overheat the engine! Also note that the temperature alarm assumes that there is coolant in the system which transfers the heat to the sensor. It is possible that if you lose the coolant, the engine could overheat and seize before the sensor gets up to its switch temperature!
For starters, though, if the alarm stops sounding when the engine starts (removing any input from the charge circuit and the oil pressure sensor) then at least you know that the sensor is not permanently alarming. Most sensors simply unscrew from their housing and can then be dipped in boiling water to test them. During such a test, you can either disconnect the other alarms to silence them or you could block off the mounting hole and run the engine to silence the alarms. It's probably easier and safer to disconnect the alarms from the buzzer so as to test the whole circuit through the buzzer for the function on test. I guess it sounds more complicated than it really is - I'd think the greatest risk is scalding yourself when you dip the sensor!
Do you have the circuit for your panel?
Rob.
For starters, though, if the alarm stops sounding when the engine starts (removing any input from the charge circuit and the oil pressure sensor) then at least you know that the sensor is not permanently alarming. Most sensors simply unscrew from their housing and can then be dipped in boiling water to test them. During such a test, you can either disconnect the other alarms to silence them or you could block off the mounting hole and run the engine to silence the alarms. It's probably easier and safer to disconnect the alarms from the buzzer so as to test the whole circuit through the buzzer for the function on test. I guess it sounds more complicated than it really is - I'd think the greatest risk is scalding yourself when you dip the sensor!
Do you have the circuit for your panel?
Rob.
Grinder
New Member
Earlier I used to work with electronics and designing of monitoring systems on MAN marine diesel engines. And one of the things we did most often when we were on the boats, was to test the sensors/alarms on big complicated monitoring system and also on simple circuits like you have described.
If you want to boil the sensor, that is a good solution. Unfortunately on many engines you'll then need to drain all the fresh water from the engine before you remote the sensor, to avoid spilling water all over your engine room.
On these types of simple monitoring systems that you describe here, I guess you have one coolant water sensor for you're analogue gauges, and one coolant water alarm sensor for the alarm. The alarm sensor is often equipped with 3 connections (1. Common, 2. Normally open, 3. Normally closed), but if you have negative(-) to ground (like in a car) then the engine itself will be common.
If you have an alarm switch on the coolant water, do the following to test the alarm:
1. Put the ignition on and start the engine. This is to clear out all the other alarms that will be activated when you only have the ignition on.
2. Remove the plug(s) from the coolant alarm sensor. If it is several contacts on the alarm sensor, remember which cable/plug is connected where.
3. If the alarm sounds when you remove the alarm sensor, then you know the alarm itself is working! If not, put a piece of wire between the two plugs that was connected to the alarm sensor. Now the alarm should sound.
If you have a combined coolant water sensor which both shows the temperature on the analogue gauges and controls the alarm indication, this is not the way to do it. Then you can find out what type of sensor you have, and find a data sheet for this sensor on the internet. Normally you'll find a table that shows which temperature values that relates to which resistance values. So instead of putting a wire between the plugs that you have disconnected, you can put a resistor that matches for example the resistance value you need to have 100 degrees celsisus water temperature. When you simulate 100 degrees water temperature, the alarm should sound!
Hopefully this was of any help! Please ask if you need more help.
If you want to boil the sensor, that is a good solution. Unfortunately on many engines you'll then need to drain all the fresh water from the engine before you remote the sensor, to avoid spilling water all over your engine room.
On these types of simple monitoring systems that you describe here, I guess you have one coolant water sensor for you're analogue gauges, and one coolant water alarm sensor for the alarm. The alarm sensor is often equipped with 3 connections (1. Common, 2. Normally open, 3. Normally closed), but if you have negative(-) to ground (like in a car) then the engine itself will be common.
If you have an alarm switch on the coolant water, do the following to test the alarm:
1. Put the ignition on and start the engine. This is to clear out all the other alarms that will be activated when you only have the ignition on.
2. Remove the plug(s) from the coolant alarm sensor. If it is several contacts on the alarm sensor, remember which cable/plug is connected where.
3. If the alarm sounds when you remove the alarm sensor, then you know the alarm itself is working! If not, put a piece of wire between the two plugs that was connected to the alarm sensor. Now the alarm should sound.
If you have a combined coolant water sensor which both shows the temperature on the analogue gauges and controls the alarm indication, this is not the way to do it. Then you can find out what type of sensor you have, and find a data sheet for this sensor on the internet. Normally you'll find a table that shows which temperature values that relates to which resistance values. So instead of putting a wire between the plugs that you have disconnected, you can put a resistor that matches for example the resistance value you need to have 100 degrees celsisus water temperature. When you simulate 100 degrees water temperature, the alarm should sound!
Hopefully this was of any help! Please ask if you need more help.
fisherman
Well-Known Member
No, its a standard Mermaid loom, I can ask them. Thinking about it I'm guessing the oil sender is close circuit at rest, so sounding the alarm, and the heat sender will be open circuit at rest, so no alarm. I can disconnect the oil sender, but to stop the 'switch on' alarm I would have to short the wires, then I could take out the heat sender and boil it.
