Make your own temp alarm?

[Kman]

As our boat’s lower unit seems to be a trash bag magnet (and I’m an inveterate tinkerer) , it would seem prudent to put some sort of high temp alarm on the motor to give us a warning that something is amiss. Those lightweight outboards heat up FAST when they are starved for water. Ya, there are water temp and pressure gauges, but what are the chances you'll scan them during the 30 seconds or so it takes to fry the motor?

The motor is a dinosaur (1980s Japanese-made 40HP Mariner), so there’s no built-in warning system of any kind—other than seize, that is. If you have a good ear (which I don’t), you can hear a change in the exhaust note when you wrap a bag or kelp leaf. It sounds more “throaty”. We've had a couple close calls in the last boat and one so far on this one—anyone else heard that “crinkling paint” sound and see only steam coming out the pisser?

Doesn’t look like making a temp alarm it is that hard to do. Digi-Key sells a sealed TO-220 packaged temp switch with preset operating temperatures and normally open contacts. You could JB Weld one of these rascals to the head and wire it to an alarm. The contacts are good for 1 amp--plenty of juice to make noise and light LEDs.



Anybody else tried this? Just might save a motor, especially for us guys based in trash bag heaven--Long Beach, Ca.

Kurt

[Bobber3]

I installed one on my fan cooled enclosed generator to shut it down if over heats Normally open, closes to ground the ignition. My yamaha is supposed to go to safe mode and sound its own alarm I trust.

[Kman]

Seems like it would be worth a shot. Shoot, the parts can be had for ~$25.

[baypro21]

sure, go for it. If you know what normally open and normally closed means you will have no problem wiring it up. Sounds like a good idea.

[Kman]

baypro21 - 1/21/2007 6:04 AM

sure, go for it. If you know what normally open and normally closed means you will have no problem wiring it up. Sounds like a good idea.

I was a motor control electrician back in college, so no problem with the NO/NC thing. Need to do some WOT driving and zap the head with an IR thermometer, then do the same while slow driving when the thermostat is controlling things (there's a poppet bypass for high rpm), and buy sensors 10 or so degrees above the max reading. Prolly should consider that today's water temp (54 deg) is ~ 20 degrees less than I will encounter in the Summer.

What I'd really like to build is a pressure switch, hooked up to the cooling system that would alarm when the pressure dropped below some level. I'm sure the parts are out there, but I bet they're more $$$ and the acid, er, saltwater will eat the sensor in no short order.

Edit: Doesn't have to be temp. How about pressure? Pressure switches are all over.