Checking the water temp sender

[RAD88]

This applies to a Yanmar YSB12.

Anybody have an idea how to trouble shoot the water temp sender on a boat with no gauge and only idiot lights?

What is the proper way to winterize this small engine ?
How do you know when the thermostat has opened when you have no gauge?

I have done a bit of research but am interested in some input.

 

[All U Get]

Try this Rad88:
http://www.pbase.com/mainecruising/engine_temp

All U Get

 

[Ian McGain]

I have spent 10 years on the hard at my marina in the middle Chesapeake Bay. To winterize my YSM12, I pull the hose after the raw water filter and place a funnel in the hose. I hold the hose as high as it will go, and fill with -100 degree anti-freeze from West Marine. I have considered the less expensive pink but my peace of mind is worth another $15.00. I have another person start the engine and pour in two gallons into the funnel. When two gallons have been pulled into the engine, the person in the cockpit pulls the stop leaver and I pull the funnel, placing my thumb over the hose, reattach to the raw water filter. This is while the boat is in the water prior to pulling. To stop the engine you may also use a spray fog is you wish. After this excercise, I change the oil.

I beilieve the water temputure does not go over 100' F so I do not know if temputure guage will be of any help. The red light and buzzer will give you a warning and also I allways check that I am pushing water out the stern everytime i start the engine and also when underway.

If you sail May through November, you do not require a thermostat, and may consider removing since this is a raw water system.

Hope this helps

Ian
Meant to Be
1979 Hunter 30'

 

[RichH]

Checking the operation of the simple idiot light sensor used on most Yanmars is quite easy. These devices are simple 'thermo-switches' .... when the switch reaches its set point (typically near the boiling point of water 100°C/212°F) the switch 'closes' and current flow in the entire circuit including the idiot light and the 'buzzer'. When the device is at less than the set point temperature the switch is 'open' and no current flows.

How to check the temperature idiot light:
1. Remove the wire from the screw-in plug AT the engine. Touch the bare wire (connector actually) to a clean bare spot on the engine. If the buzzer and the light comes on, the circuit to the switch is intact, If not you have a faulty circuit and need to make repair.
2. Remove the thermoswitch and check its 'continuity' with an 'ohm' meter. If near zero ohms, when the switch is near ambient temperature the switch is 'shot' ... but if reading zero ohms it would have caused the buzzer and the light to come on at all times .... if not, ..... put the switch in BOILING water and let 'soak' for a time then quickly remove and measure ohms across the insulated wire post and the 'body' of the switch, if you read ZERO ohms the switch is OK, if 'much' less than ZERO ohms the switch is 'shot'.

Simple to remember ... the thermally HOT switch becomes 'closed' = zero ohms and the circuit is energized allowing the circuit to be 'grounded' through the engine. To check the set point (can be either 150F, 180F or 212+F° depending on the engine - read your engine specs. , the thermoswitch usually has the same set point as the thermostat plus ~10-20 degs.), use an indirect infrared thermometer and simply read the IR thermometer for at which temperature the 'switch' allows the circuit to 'ground' through the engine.

Always check the integrity of engine to battery ground for 'continuity' (zero ohms resistance) **first**, before doing such ohms/resistance testing, as if that engine ground circuit has high resistance, the switch wont work and the testing will be for 'nothing' .... and this includes testing the oil pressure switch and the alternator switch idiot light circuits ... they all 'ground out' through the engine-to-battery ground connection).

 

[kloudie1]

Quick note.. Since that engine is raw water cooled, the temperature set point on the alarm switch is 140F .. The thermostat on the engine should start to open at a little over 100F and be fully opened around 125F.. As rich says both these components are easy to test using a thermometer and hot water and an ohm meter..

 

[Rob19574]

I have a very similar YSM engine - its the YSM12. Do as described above. In addition, I let the engine run for about 10-15 minutes to warm up first using fresh-water to run thru the system. This ensures the thermo is open and you flush out all seawater / salt. Then I shut her down and open the drain-valve located under my block / head. This drains all the water out of the block and head. After its drained, rig the raw-water intake line such that the anti-freeze can enter the system and restart the engine. Once I see the pink-stuff come out of my exhaust system I wait about a minute and shut everything down. I have a zinc plug on the top of my block I open it to ensure anti-freeze is inside the block (meaning the termo opened and safely filled the block) - perhaps the YSB has one too? If not, try the thermo and check for anit-freeze on both sides.

Then change the oil and spray down the block with CRC or WD40 -- your set for the winter.

- Rob