MD2010/2020/2030/2040 high temperature alarm switch

[MikeBz]

Subsequent to my engine throwing out a litre of coolant some time before the high temp alarm sounded, I removed the switch (Volvo Penta Shop £60.72!!!) and stood it upright in pan of water, immersed to halfway up the hex/nut section. Heated it up to simmering point, after 10 minutes it was still open circuit. Bought a replacement from a well-known online engine parts retailer (£25) and ran the same experiment with the same result. In both cases they remained completely open circuit. I thought these were supposed to switch at 92C - am I wrong? Is my testing methodology wrong (it's hard to see how)?

 

[Bilgediver]

Maybe you are testing the temperature gauge sensor. Check if the resistance varies with temperature.

 

[MikeBz]

There is no temperature gauge sensor. (If fitted then it’s a different part). It’s completely open circuit (20M Ohm range!).

 

[Alex_Blackwood]

Subsequent to my engine throwing out a litre of coolant some time before the high temp alarm sounded, I removed the switch (Volvo Penta Shop £60.72!!!) and stood it upright in pan of water, immersed to halfway up the hex/nut section. Heated it up to simmering point, after 10 minutes it was still open circuit. Bought a replacement from a well-known online engine parts retailer (£25) and ran the same experiment with the same result. In both cases they remained completely open circuit. I thought these were supposed to switch at 92C - am I wrong? Is my testing methodology wrong (it's hard to see how)?

How did you measure the water temp? What was it?

 

[MikeBz]

With a cheap digital meat thermometer, but given that the water was boiling and I’m close to sea level then it’s guaranteed to be within a gnat’s of 100C anyway.

 

[VicS]

Subsequent to my engine throwing out a litre of coolant some time before the high temp alarm sounded, I removed the switch (Volvo Penta Shop £60.72!!!) and stood it upright in pan of water, immersed to halfway up the hex/nut section. Heated it up to simmering point, after 10 minutes it was still open circuit. Bought a replacement from a well-known online engine parts retailer (£25) and ran the same experiment with the same result. In both cases they remained completely open circuit. I thought these were supposed to switch at 92C - am I wrong? Is my testing methodology wrong (it's hard to see how)?

95C according the the W/S manual ........... but certainly should have closed in boiling water !

£25 is a lot less than VP's list price but if your supplier is who I think it is they are generally considered to be reliable. I think I would contact them.

 

[MikeBz]

I contacted the supplier, they agree that if it stays open circuit in boiling water then it's likely to be faulty and have asked if I would like a refund "... as it wouldn't be a good idea to send you a replacement". I'm not sure whether that's implying they are all likely to be faulty or whether they don't trust me with a replacement! I've accepted the refund.

I'm considering fitting a NASA EX-1 exhaust gas temperature gauge/alarm - the only snag is that according to the instructions "The display unit is not watertight and must be mounted in a dry area" so really it needs to mounted down below, in which case the alarm won't be heard from the cockpit. Hmmm.

 

[rogerthebodger]

If its just an over temperature switch I used one of these connected to a LED and buzzer with the 12 Vdc taken from the ignition / run switch

https://www.amazon.com/Hilitchi-The...fix=bimetal+temperature+switch,aps,531&sr=8-3

 

[BabaYaga]

If its just an over temperature switch I used one of these connected to a LED and buzzer with the 12 Vdc taken from the ignition / run switch

https://www.amazon.com/Hilitchi-Thermostat-Temperature-Assortment-Appliances/dp/B07KF3KN18/ref=sr_1_3?crid=2WNHOMKM0UGZI&keywords=bimetal+temperature+switch&qid=1689606905&sprefix=bimetal+temperature+switch,aps,531&sr=8-3

I use the same type of switch placed on the exhaust elbow, wired in parallel with the ’normal’ temp alarm switch on the engine block. So if either of them trips, the ’normal’ warning light and buzzer on the engine control panel will activate.