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Discussion Starter · #1 ·
I have an M25XP, panel has an oil pressure alarm but no water temperature alarm. There is only one place in the thermostat housing for a sender and that is used for the water temp gauge.

I have seen a replacement housing for lots of money that will allow for a second sending unit (switch) for an alarm. But there must be an easier way...

Anyone know one? Some sort of peel and stick or clamp on solution? :)
 

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Sounds like you are referring to the temperature of the coolant inside the engine. However, most would test the exhaust temp on a marine engine, which can be done with a simple band around the exhaust. If the exhaust temp is too high, it suggests that raw cooling water isn't circulating properly. This does not guarantee that internal cooling temps are proper, but it addresses 99% of the issue.
 
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My M25 had a T fitting where the water temperature sender was mounted. I didn't like this because it always read low. Here is a pic;


I fixed the problem by replacing the thermostat (among other things), and; while I had the thermostat housing off, I drilled and tapped a new sender hole in the thermostat housing. Like this;


Sorry, I don't remember the drill or tap size, but if you can't figure that out, perhaps you should not attempt this upgrade.
 
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Discussion Starter · #5 ·
Some fascinating and diverse answers here. More than one way to skin a cat. I have also found the Aqualarm #212 Engine Overheat Detector which bolts somewhere on the block. Thanks all.
 

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BTW - the reason that it read low is that I believe that an air bubble would get trapped in the T fitting... Also, the T was not in the flow of water through the system.
My M25 had a T fitting where the water temperature sender was mounted. I didn't like this because it always read low. Here is a pic;
My drill and tap fix addressed these issues.

Finally, you should know that the thermostat housing is aluminum, and therefore is very easy to drill and tap.
 
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The exhaust sensor is to detect loss of raw water injection into the exhaust. Without this the water lift muffler and other components will see exhaust temperatures and melt or otherwise fail. Sensing engine cooling water temp tells you what the engine is seeing, which a different thing. For example it would show you if the freshwater side cooler was plugged up or if the fresh water pump was failing. I think you need both.
 
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