Add-On Outboard Motor Overheating Alarm?

minuteman62-64

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Running my boat in San Diego Bay today - focused on staying out of the way of a variety of Navy vessels/Homeland Security Escorts/pleasure boats/etc. Wasn't totally focused on my cylinder head temperature gauge. Water intake blocked by a piece of kelp and the motor overheated.

So, I'm wondering, is there an add-on alarm that will work in conjunction with my cylinder head temp. gauge? Something that will give a loud sound when the temperature exceeds a set level?

The motor is a '82 30 HP Mariner, as noted, equipped with a cylinder head temperature gauge.
 

Chris1956

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Re: Add-On Outboard Motor Overheating Alarm?

I will bet you can buy a system, however, it would be real easy to make one up out of parts. The temp sensor grounds when the heat exceeds 190*F. So wire an alarm with +12VDC from the ign keyswitch, in series with the sensor and you got it.
 

Texasmark

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Re: Add-On Outboard Motor Overheating Alarm?

I will bet you can buy a system, however, it would be real easy to make one up out of parts. The temp sensor grounds when the heat exceeds 190*F. So wire an alarm with +12VDC from the ign keyswitch, in series with the sensor and you got it.

Only question is adaptation. One thought is to get a conventional sensor and just epoxy onto the top of the block with a big blob of epoxy so as to improve the thermal transfer....like bury the sensor in the epoxy, covering it completely up. Cleaning the area down to raw alum would help it to stay in place.

You would want a conductive epoxy, something with metallic particles embedded in it. JB weld is such a critter. The particles are steel, and not the best conductor but since you don't need much current to operate the alarm, and you would have a large mass of epoxy in contact with the block it should work ok.

Considering the alarm might run on 200 milliamperes, with at least 10 volts across it, would allow you a resistance between the case of the sensor and the block of 2/.2 = 10 ohms. That's a lot and you should have no problem getting below that number.

If you use a digital meter in making your ohm measurements, they don't have the zeroing function like the old analog meters and you need to get your lead resistance out of the circuit. So touch your leads together on your lowest scale and get the number then measure your sensor case to engine block resistance once installed and subtract the difference. If less than 10 ohms you should be in great shape.

Mark

After thought. I had a '75 70 hp rude that had a stat that stuck shut. I was running WOT one day not knowing that and seized an engine.....$1000 for machinist block work with new pistons and all, and I did all the rest. Had that engine an alarm, I would not have been out the cash. Great idea of yours.
 

minuteman62-64

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Re: Add-On Outboard Motor Overheating Alarm?

OK, that would be a way to go. Any ideas on a source for a sensor? The only one I can locate (here on iboats) seems to measure 1 1/2" x 3" - no place to fit something that large on the head of my little 2 cyl. 30 HP motor.

I was hoping, since I already have a cylinder head sensor hooked up to a gauge, that I could somehow use that sensor to also sound an alarm. If I could find another sensor of the type you describe, approximately the same size as the one I have (about 3/4" x 1/2") that would be no problem to mount and easy to wire to an alarm. Of course I also have to locate a water proof alarm.
 

Home Cookin'

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Re: Add-On Outboard Motor Overheating Alarm?

I think I'd rig the sensor to the motor, not the guage, so that if the guage fails, the sensor is still viable.

You may research to see if there is a fitting for one; many outboards are equipped with an alarm while few have guages,
 

Texasmark

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Re: Add-On Outboard Motor Overheating Alarm?

Most later model engines have them from the factory. Only problem is getting one that doesn't have a built in bracket for mounting in a conventional fashion which would make for a really big blob.

Temp you want is about 190F with reset around 170F. That's what my '02 Merc uses with a 143 stat.

I pulled up Bimetal Thermostats, Temperature Controls & Thermostatic Switch and went to their thermostats snap disc section and found something that might work. First of all it's $10. Second it is hermetically sealed and it has 2 wires attached so you can just lug one to the engine block and lug on a wire to the other one to go to your horn low side. Makes no difference which is which.

Pull up the site and if they have a search engine, the basic part number is: 2570F068. That is a "close on rising temp" switch. Then you have to select the temp. Once you pull up the picture of that switch, go down the page to a window that allows you to select the temp.

The 180F-214 is what I think you want. It closes at 180F and opens at 165F +/- 5.

You can work through the part number in the checkout section, or give them a call. The part number may come up something like:

2570F068-180F-214

There are 2 ears on it for mounting. The sensor is the round part in the middle. The way I would mount this would be to put a blob of conductive epoxy on your cleaned off block and just push this down into it till it quits moving. With the flange and all you will have plenty of surface area in contact with the block and it should work just fine. It says that overall it's 1" but that surely is the ears. Not too big and the price is right.

Good Luck,
Mark
 

Chris1956

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Re: Add-On Outboard Motor Overheating Alarm?

Mark, The sensor would need to allow all the current running thru the buzzer to get to ground. It will be about 3A I would think.
 

Texasmark

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Re: Add-On Outboard Motor Overheating Alarm?

Most later model engines have them from the factory. Only problem is getting one that doesn't have a built in bracket for mounting in a conventional fashion which would make for a really big blob.

Temp you want is about 190F with reset around 170F. That's what my '02 Merc uses with a 143 stat.

I pulled up Bimetal Thermostats, Temperature Controls & Thermostatic Switch and went to their thermostats snap disc section and found something that might work. First of all it's $10. Second it is hermetically sealed and it has 2 wires attached so you can just lug one to the engine block and lug on a wire to the other one to go to your horn low side. Makes no difference which is which.

Pull up the site and if they have a search engine, the basic part number is: 2570F068. That is a "close on rising temp" switch. Then you have to select the temp. Once you pull up the picture of that switch, go down the page to a window that allows you to select the temp.

The 180F-214 is what I think you want. It closes at 180F and opens at 165F +/- 5.

You can work through the part number in the checkout section, or give them a call. The part number may come up something like:

2570F068-180F-214

There are 2 ears on it for mounting. The sensor is the round part in the middle. The way I would mount this would be to put a blob of conductive epoxy on your cleaned off block and just push this down into it till it quits moving. With the flange and all you will have plenty of surface area in contact with the block and it should work just fine. It says that overall it's 1" but that surely is the ears. Not too big and the price is right.

Good Luck,
Mark

After this posted, the www address changed. In the event of confusion, the company www address for this switch is senasys and then .com.
 

minuteman62-64

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Re: Add-On Outboard Motor Overheating Alarm?

Most later model engines have them from the factory. Only problem is getting one that doesn't have a built in bracket for mounting in a conventional fashion which would make for a really big blob.

Temp you want is about 190F with reset around 170F. That's what my '02 Merc uses with a 143 stat.

I pulled up Bimetal Thermostats, Temperature Controls & Thermostatic Switch and went to their thermostats snap disc section and found something that might work. First of all it's $10. Second it is hermetically sealed and it has 2 wires attached so you can just lug one to the engine block and lug on a wire to the other one to go to your horn low side. Makes no difference which is which.

Pull up the site and if they have a search engine, the basic part number is: 2570F068. That is a "close on rising temp" switch. Then you have to select the temp. Once you pull up the picture of that switch, go down the page to a window that allows you to select the temp.

The 180F-214 is what I think you want. It closes at 180F and opens at 165F +/- 5.

You can work through the part number in the checkout section, or give them a call. The part number may come up something like:

2570F068-180F-214

There are 2 ears on it for mounting. The sensor is the round part in the middle. The way I would mount this would be to put a blob of conductive epoxy on your cleaned off block and just push this down into it till it quits moving. With the flange and all you will have plenty of surface area in contact with the block and it should work just fine. It says that overall it's 1" but that surely is the ears. Not too big and the price is right.

Good Luck,
Mark

Looks like a good option. The Aqualarm site had a complete package for about $80. Looks like I can get the sensor through these folks for about $10 and an alarm from iboats for about $20 - maybe more economic sense for my '82 motor.

Not sure about the best temperature range. The Aqualarm unit closes at 200 F (no info on opening temp.). My gauge indicates a temperature of 180 F at cruising speed (not sure of accuracy, although it tracks w/my HF remote temp. sensing gauge at idle, on the muffs). I've noticed that when my water intake gets clogged (those times when I'm not distracted with challenging navigation so I can monitor the gauge) the gauge reading shoots up very quickly. So, I'm thinking maybe the 200F (closes at 200, opens at 185) would be the way to go.

Anyways, I see a solution. Thanks, guys.
 

minuteman62-64

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Re: Add-On Outboard Motor Overheating Alarm?

Just thought of another question. The sensor that Texasmark referred to me is a two wire sensor. The Aqualarm sensor also appears to be a two wire sensor. For the two wire sensor, wouldn't I be looking for good thermal conductivity instead of good electircal conductivity?
 

Texasmark

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Re: Add-On Outboard Motor Overheating Alarm?

Of course. That's why you use a metal impregnated epoxy. We used to use a silver impregnated epoxy in industry. Then there is alum impregnated, then is JB weld with steel.

Anything you do will beat where you are. Earlier you were begging, now you are getting picky. If you want it done professionally, buy a new engine with one professionally installed!!!!

Mark
 

roscoe

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Re: Add-On Outboard Motor Overheating Alarm?

Before ordering, you might want to take an infrared temp sensor and get some "normal" temp readings off the head, where you plan to attach.

Internal temps, external temps, water jacket temps, will all vary from motor to motor.
Even location on the head will make a difference.

Anyway, my point is, that you may want to use a lower temp switch.
 

minuteman62-64

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Re: Add-On Outboard Motor Overheating Alarm?

Of course. That's why you use a metal impregnated epoxy. We used to use a silver impregnated epoxy in industry. Then there is alum impregnated, then is JB weld with steel.

Anything you do will beat where you are. Earlier you were begging, now you are getting picky. If you want it done professionally, buy a new engine with one professionally installed!!!!

Mark

Nope, not picky, just want to make sure I understand all the input. I was reading some of the above posts as indicating that a good electrical contact is needed between the sensor casing and the engine block. It just seems like with a two wire sensor I wouldn't need any electrical contact with the block - just good heat transfer.
 

Texasmark

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Re: Add-On Outboard Motor Overheating Alarm?

Yes sir. Originally my thoughts were on the OEM installed switch, like in my engine which is a single wire going to a switch embedded in a bracket that is screwed to the rear of the block of the engine. In my OEM engine installation, you need electrical and thermal conductivity.

The switch I researched for you didn't have the electrical conductivity problem since it had an input and output wire that could be electrically secured reliably. My original answer was considering the electrical conductivity of the JB weld to ensure that it could carry enough current to satisfy the circuit but now that is not a concern; you have a separate wire provided for that.

On the remainder, thermal conductivity, you probably won't notice 10 degrees difference, if that much, between the block temp and the sensor on the switch if you mount it as I said: Make a JB puddle on a cleaned down to the alum spot on the block; depress the switch down into the puddle till it stops moving and let it cure.

Mark
 

minuteman62-64

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Re: Add-On Outboard Motor Overheating Alarm?

OK, received my alarm from iboats. I'll hit it w/12 volts tomorrow to see if it will be loud enough. If OK I'll order one of the 2570 series thermostats from Senasys. Looking at either: Close 180 degrees-open 165 degrees or close 200 degrees-open 185 degrees. They are cheap, so I may get both and experiment with locations and thermostats to get the best match.

Mounting on my cylinder head will be a challenge since the thermostat unit is a lot bigger than the sensor for my cylinder head temperature gauge (it's about 1 inch diameter) - I'll probably be back looking for help/advice with the mounting.

Next issue is the wiring. I'll be asking for advice on that in another post.

Thanks, guys.

If
 

Texasmark

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Re: Add-On Outboard Motor Overheating Alarm?

15 degrees won't matter all that much. I picked the one I did as it was closest to the temperatures that my manual says mine operates.

The stat in my engine is stamped 143F. Manual says that opening temp will be within 5 degrees. Obviously, as the temp in the head rises it will open farther and by the time it is fully open the water could be up to 160. That leaves 35 degrees of margin on the closing temp of mine. If your gauge is reading what it is, need to verify if accurate.

Only thing I can think of is your hot water heater. If domestic US, on Normal setting it is usually 140F. You could pull your sensor and put it in a cup of hot water and see what it says.

Wiring is a piece of cake. Series DC circuit. Engine block to sensor lead. Sensor lead to one side of horn. Other side of horn to 12v anywhere you find it. Wire size 16 AWG is common in wiring and will more than handle the current. Crimp on terminals is the easiest. Auto parts store probably has a terminal kit with terminals and crimper. Ask a salesperson how to use it if directions are inadequate. Harbor Freight has them for sure.

On the sensor, makes no difference which is which. On the horn probably not also, but check. If it has a + marked next to a terminal that goes to the 12v.

Good luck,

Mark
 
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minuteman62-64

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Re: Add-On Outboard Motor Overheating Alarm?

15 degrees won't matter all that much. I picked the one I did as it was closest to the temperatures that my manual says mine operates.

The stat in my engine is stamped 143F. Manual says that opening temp will be within 5 degrees. Obviously, as the temp in the head rises it will open farther and by the time it is fully open the water could be up to 160. That leaves 35 degrees of margin on the closing temp of mine. If your gauge is reading what it is, need to verify if accurate.

Only thing I can think of is your hot water heater. If domestic US, on Normal setting it is usually 140F. You could pull your sensor and put it in a cup of hot water and see what it says.

Wiring is a piece of cake. Series DC circuit. Engine block to sensor lead. Sensor lead to one side of horn. Other side of horn to 12v anywhere you find it. Wire size 16 AWG is common in wiring and will more than handle the current. Crimp on terminals is the easiest. Auto parts store probably has a terminal kit with terminals and crimper. Ask a salesperson how to use it if directions are inadequate. Harbor Freight has them for sure.

On the sensor, makes no difference which is which. On the horn probably not also, but check. If it has a + marked next to a terminal that goes to the 12v.

Good luck,

Mark

Yeah, I'm leaning to the lower temperature range - figure it's better to have the alarm kick in a little too early than a little too late. Plus, I'm not sure if I'm going to be able to get a great heat transfer with my potential sensor/thermostat mounting locations.

On the wiring, I'm thinking pretty much as you mentioned. Only thing different is the addition of a test switch - probably mounted near the ignition - for a pre-start buzzer test. See attached schematic. Only thing I'm not sure of is the advisability of switching to ground for the test. Appreciate any thoughts.
 

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Texasmark

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Re: Add-On Outboard Motor Overheating Alarm?

Excellent schematic. Assume the test switch is a momentary on, SPST (push button or spring loaded toggle) Looks like you "got-r" covered.

Mark
 

minuteman62-64

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Re: Add-On Outboard Motor Overheating Alarm?

OK, received the thermostatic switch (good response from those folks). Going to be a bit of a challenge mounting it on my little cylinder head. See attached photo showing thermostatic switch dangling in front of head. Upper right you can see the sensor for my temperature gauge (with the yellow wire coming from it) - quite a bit smaller than the thermostatic switch.

I appreciate the suggestions about using a heat transfer epoxy to fasten the element. However, I'm kind of anal in that, when I put something together I do it with the thought that, someday, someone (probably me) is going to have to disassemble it :( So, I'll be trying a few ideas and running them before you guys for input. I'll start by getting out my trusty HF remote temperature sensor, running the motor and "mapping" the cylinder head to see where potential hot spots are.
 

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