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  #1   IP: 207.118.20.35
Old 05-15-2013, 07:57 PM
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capnward capnward is offline
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temperature gauge and alarm sensors on same fitting

Esteemed a-fourians,
I have a temperature sensor for the temperature gauge, and a sensor for a new temperature alarm buzzer, on opposite ends of a t-fitting mounted on the front of the head, where the gauge sensor used to be by itself. The alarm buzzer now buzzes when the engine is warmed up, i have turned it off, and turn the ignition switch to restart it again. It doesn't alarm when the engine is running, only when I turn it on again when it's warm. Apparently the water gets hotter in the engine when it stops flowing through it. Although the alarm sensor is supposed to activate at 200 degrees, when it does activate, the temperature according to the gauge is only 170 degrees. Since the two sensors are 2 inches away from each other on the same t-fitting,why does this happen? I was expecting the temperature gauge to read a little cooler because it is no longer attached as close to the engine coolant flow as it was, and I think it is reading cooler, not much, maybe 10 degrees. I was not expecting the alarm to go off when the gauge shows the temperature is ok. The alarm sensor is by Aqualarm, part #20118. I did not purchase the moyer temperature and oil warning kit, because I just wanted a temperature alarm, but the fitting for the temperature sensors on the front of the engine is very similar. I disconnect the alarm when it goes off, and keep running, and all is well according to the gauge, so I haven't yet tried leaving the engine running with the alarm going to see if it the buzzer eventually turns off as the coolant flows through the block again. It probably would. I suspect I bought a temperature alarm sensor that is not accurate, and triggers the alarm before it should.
I just thought of another possibility; the t-fitting is mounted vertically, with the alarm sensor on top, so it doesn't interfere with the oil fill port. I see in the image of the moyer kit that the fitting is turned so it's horizontal. Maybe heat rises to the top of the fitting, creating a significantly higher temperature for the alarm sensor than for the gauge sensor. Does this sound likely? Or should the orientation of the t-fitting not make any difference? I could try reversing the sensors, or turning the fitting so that it's horizontal, but it could be a waste of time. I think more likely I need to get a Cole-Hersee sensor like the one in the Moyer kit, and see if it's any more accurate than the one by Aqualarm. The engine is fresh water cooled with the heat exchanger sold by Moyer. Your thoughts, please?
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  #2   IP: 96.229.18.9
Old 05-16-2013, 09:18 AM
Dave Neptune Dave Neptune is online now
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Question Be sure

capnward, first welcome to the Afourian forum. Are you sure of your temp gage? It may be off and the alarm is fine.
When the engine is shut down all of the "heat" that has been radiating into the cooling water and carried away is now trapped inside the engine. When the engine is shut off the "heat" has nowhere to go so the temp of the engine rises as the "heat" in the core of the beastie radiates into the rest of the block.

Dave Neptune
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  #3   IP: 207.118.20.35
Old 05-16-2013, 02:40 PM
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I'm kinda sure

Hi Dave, thanks for the reply. I bought the temperature sensor and gauge from Moyer last July. I assume it's good, but how do I know? The needle goes up and down like it should. Lately it stops going up at 170 degrees or so.
I've never noticed it climbing into a higher temperature after I shut down, because it's disconnected when the ignition switch is turned off. I do know that the buzzer goes off when the gauge is reading nowhere near 200 degrees. This hasn't happened when engine is running, only when I restart it when it's warm. Maybe the alarm sensor takes longer to revert to it's original position as the engine cools than the gauge sensor does. If the alarm sensor is accurate, and engine temp is actually exceeding 200 degrees with the engine shut down, is this damaging to the engine? Do I have some kind of cooling restriction? When I'm out on the boat today, I will let it run at lower rpm and in neutral for a few minutes before shutoff, and see if the buzzer still goes off with the gauge reading low. Someday when there are no customers aboard I will keep it running with the buzzer on to see if it stops as coolant flows again, but that is a little scary to do if I'm not sure the gauge is reading right. I was trusting the gauge reading until I saw your post.
This could be related: There has been no regular thermostat in the engine for 15 years or so, the people who rebuilt it didn't recommend one. Instead I installed a Thermostatic Mixing valve, it think i bought it from Indigo, it's a Honeywell AM Series, and allows me to adjust the engine temperature as well as act as a thermostat. It's mounted next to the heat exchanger. It has always worked fine. I have noticed, when the engine shuts down, that coolant flows up the hose into the overflow tank above the heat exchanger. I assumed this is normal, because the heat exchanger is filled to the top and the water has nowhere else to go when it's hot and expansive.
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Old 05-16-2013, 02:54 PM
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will try turning fitting horizontal

After finding the forum thread entitled 'installed alarms now engine temp not right', I see that the t-fitting should probably be horizontal, or air may get into the top end where the alarm sensor is. I will try that.
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  #5   IP: 71.118.13.238
Old 05-16-2013, 05:27 PM
Dave Neptune Dave Neptune is online now
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Lightbulb Checks!!

capnward, try turning the ignition back on after the engine has sat for a few minutes after running and see what the temp gage reads then, it will probably read much higher (10~15 degrees or more)!!
If the gage is fairly new it is probably fine.
Your dual port set-up may read a bit cooler however because of the lack of a lot of air moving aroung the sensors they probably read pretty close.
Keep- in mind a temp rise after shutting down ir NORMAL! This "rise" may be setting off the alarm.

Dave Neptune
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  #6   IP: 128.183.140.38
Old 05-17-2013, 10:33 AM
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Quote:
Originally Posted by Dave Neptune View Post
Keep- in mind a temp rise after shutting down ir NORMAL! This "rise" may be setting off the alarm.

Quite right. I have the same thing happen on my FWC A-4. It is easily avoided by running at idle in neutral for a few minutes before suntting down.
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