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Old 22-10-2021, 06:33   #1
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thermostatand my high heat issue

Dear All ... thanks for previous commentary here. Very useful. Another thing discovered this morn. See pic below. There are 2 wires connected to the thermostat housing. Red and yellow. In pic see the red is disconnected. It was "partially" connected. I can secure it by pushing it manually together although IMHO its not a super tight way to connect that wire. My question is what is purpose of wires. Is it sending of temp to gauge at console or does it have any purpose in controlling the thermostat itself and hence my over heating. fyi I plan to buy a new thermostat today if possible.
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Old 22-10-2021, 06:45   #2
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Re: thermostatand my high heat issue

It appears to be the temp sender and the wire to sender is off that sends the signal to the engine panel.
If the wire clip (inside the black plastic) doesn't hold securely look inside at the clip. It may be broken or most likely just needs to be bent back to its original shape to hold on to the sender properly.
Are you using a IR temp gun to ck. the engine temp and see if the sender is giving you the right info? Would be good to eliminate a bad sender out of the high heat problem.
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Old 22-10-2021, 06:52   #3
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Re: thermostatand my high heat issue

Thanks Billy O ! WIll do as you suggest ... however, does the thermostat use power from those wires to control temp ? Bad data to the gauge on console is one thing over heat is another. In my case for example, I can run around 2000 rpm and the temp remains at 160ish ... ie. normal. When pushed to 2400 temp rises to 179 and may go higher but I backed off. Hope my question makes sense .. thx .... Dennis
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Old 22-10-2021, 07:30   #4
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Re: thermostatand my high heat issue

It is just the sender wiring and a mechanical thermostat.
Sounds like you are depending on the temp sender to give you the correct temp reading. As suggested before, double check the accuracy of the readings from the sender.
If it is accurate, would check the usual suspects:
1. Is the prop fouled?
2. How old is the raw/salt water pump impeller?
3. Is the belt tension correct on the salt water pump?
4. Is your raw water strainer and thru hull clean?
5. Is your exhaust mixing elbow clogged?
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Old 22-10-2021, 08:59   #5
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Re: thermostatand my high heat issue

On my 4.236 the original sender had two purposes and two outputs.
Temp sender for the gauge and overtemp switch for the alarm. Maybe a PO replaced the sender with one with only the output for the gauge.
My original setup had dual purpose oil pressure sender and dual purpose temp sender. Both switches wired to an alarm, each with a separate warning light, and of course a gauge for each.
Alarms worked when I bought the boat but the gauges never did.
I have since replaced all of this an rewired the entire engine.
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Old 22-10-2021, 09:33   #6
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Re: thermostatand my high heat issue

After chasing around after high engine temp problems, and replacing senders, thermostats, wiring, etc.. on more than one engine, I have found that most of the time the problem was with the areas mentioned by other posters with poor coolant flow being #1.

The wiring has nothing to do with controlling engine temp. The fact that your coolant flow seems adequate at low RPM, but not at higher RPM indicates strongly that you have a flow problem. The first and easiest things to check are the hoses (which can look fine but are collapsed internally), strainers, and your pump impeller(s). Dive under the boat with a mask on and make sure your intake isn't clogged with weeds.

If all that looks OK, then you need to get after the harder to fix stuff. Clogged heat exchanger, mixing elbow, and the cooling passages inside the engine.
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Old 22-10-2021, 10:08   #7
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Re: thermostatand my high heat issue

Quote:
Originally Posted by kingofcary View Post
Thanks Billy O ! WIll do as you suggest ... however, does the thermostat use power from those wires to control temp ? Bad data to the gauge on console is one thing over heat is another. In my case for example, I can run around 2000 rpm and the temp remains at 160ish ... ie. normal. When pushed to 2400 temp rises to 179 and may go higher but I backed off. Hope my question makes sense .. thx .... Dennis
Everyone this the OP second post. He is indicating a temp swing from 160 to 179.

I donít believe those are over heating temps!

I would suggest looking for literature on your operating temperate for you engine.

Am I wrong here?!? Maybe Iím reading the post incorrectly.
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Old 22-10-2021, 10:16   #8
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Re: thermostatand my high heat issue

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Originally Posted by Sam Woodbridge View Post
Everyone this the OP second post. He is indicating a temp swing from 160 to 179.

I don’t believe those are over heating temps!

I would suggest looking for literature on your operating temperate for you engine.

Am I wrong here?!? Maybe I’m reading the post incorrectly.
+1.

As posted in previous thread, t'stat full opening temperature is 185F, so 179F does not appear to be a problem. For a freshwater/coolant cooled engine I would expect 185-190 as a normal temp.

And the wires have nothing to do with the thermostat operation, the thermostat (if the original) is a simple wax-pellet thermal/mechanical thermostat.

160F is not generally a good operating temperature for small diesel engines, but it is typical in raw, saltwater cooled engines because above that temperature salt precipitation can cause problems. In an engine with heat exchange higher temperatures are expected and desired.
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Old 22-10-2021, 10:27   #9
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Re: thermostatand my high heat issue

Often there are two thermostats available for an engine typically 160f and 180F. Depending on your engine room temps, water temps where you cruise, etc you pick one that lets your engine run optimally. Many engines are specked out for normal running temp of 180F.
But I choose 160F thermostats here in South Florida. Also if something fails and engine temps soar you get a little more Lea way before going to high.
With 160F thermostats my engines run between 155F - 170F. With the 180’s they ran 165F - 180F. Too close to the overheat temp of 200F for me. If an impeller fails you only have a few seconds before the engines need to be shutdown.
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Old 22-10-2021, 10:31   #10
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Re: thermostatand my high heat issue

The trick will be to remember the past operating temp. 180 is pretty normal operating temp. The thermostat opens and closes on its own no power required. Sometimes the spring gets week or corrodes and a new thermostat is required. Reconnect the wires properly as they go to your panel. The sensor may be off + or - 3 degrees but itís not important as continually running the engine at high rpm it may settle in at 185. At higher temps it will pump more water to cool.
Some advance panels have high temp alarm that is programable.
I would make a note of running temps at RPM. Run 10 min. Monitor .
At intervals 1500,2000,2500.
Sort of establish a base line of normal temps.
All the best.
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Old 22-10-2021, 10:35   #11
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Re: thermostatand my high heat issue

This is really a case of RTFM. 179F is exactly in the middle of the manufacturer's specified normal operating range.

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For the wiring, the tan (not faded red) wire goes to the temperature switch for the buzzer/alarm, the yellow goes to the temperature sender:

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Old 22-10-2021, 17:50   #12
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Re: thermostatand my high heat issue

Sounds to me that the temperatures you have are about right for the RPM.
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Old 27-10-2021, 08:22   #13
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Re: thermostatand my high heat issue

Thanks everyone for the feedback. Wanted to close this out. Net is that I did most of recommendations and the one that completely did the trick was fixing the foul3d prop. Had bottom and prop cleaned and immediately got m3 back to normal and consistent operating temp and no smoke. Appreciate this forum and you folks greatly Ö. Thanks Dennis
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Old 27-10-2021, 10:41   #14
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Re: thermostatand my high heat issue

The thermostat has a little bleed hole in it so some water flows through even with the stat completely closed. Often at low load that little bit of water is enough to keep the engine from coming up to optimum temperature. As load and temp increase, the stat starts to open and let more water through, but not until it hits around 180. So 179 + - a couple is perfectly normal. If it hits 190 you might have a problem, but won't cause damage till above 210 or so. If there is a problem it will cover that distance quick. My truck has a 195 deg stat and runs at that temp all day long, and a little higher if I'm towing or hauling something heavy. No problem. And this whole thing is why it's recommended to let the engine idle for a while before shutting it down. Better to shut the coolant supply off at 160 than 190.
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