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Old 17-08-2019, 23:02   #1
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Raw water cooling trap

Hi all,

Just had a close one, thought I would share it here in the hope it saves someone else from what could have been a costly mistake.

I haven't started the boat engine for over six months, so today I figured I should give it a run while I was working.

I did all the usual stuff, check fuel filter sight glass, check coolant, check oil, check raw water feed is on, check there is water in the strainer. All good. Press the glow button for four seconds, turn the key and the engine fired up on the first revolution. Put it in gear and brought it up to 1150 rpm, the usual cruising speed.

Glance at the gauges, oil pressure good, 24 volts and engine bank taking 50 amps of charge. Nice.

So far so good.

It was raining cats and dogs, so I rushed up on deck, looked over the back and checked to see that I was getting cooling water out the exhaust.

Check! Usual excellent flow, rushed back under cover.

Feeling good, I went below, put the ear muffs on (yes, the engine really is that noisy) and got to work on the galley build.

It took me maybe two minutes, but a little subliminal alarm bell was going off in my head. Something did not sound right. I pulled the ear muffs off and listened hard. The engine sounded fine.

Good clean purring engine note, the lovely sound of a low revving 3.3 litre diesel right on it's sweet spot.

That ain't right! Should not sound lovely. Should not purr. Should sound muffled and erratic with the giant pulses of water through the 7 meter long, 3 inch rubber exhaust pipe. Should sound like something is broken. It should NOT, repeat NOT purr like a big kitten.

No bloody water! Shut it down in a hurry and checked the exhaust temperature. Hot, but not dangerously so.

So, twenty minutes later I had removed the barnacle that was completely blocking the raw water intake, and scratching my head about how I could miss that. Then, as the system refilled I realised what had happened. There is SO much raw water in the cooling loop that it was still being processed by the cooling system when I checked over the stern. If I'd waited another moment, I probably would have seen the flow stop.

So, from now on, I don't care how much it is raining, I'm watching that exhaust water flow for a good minute or two.

Matt
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Old 17-08-2019, 23:14   #2
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Re: Raw water cooling trap

Lucky, that could have cost you 7m of new hose as a minimum if run for a few moments longer.

How about an exhaust temperature alarm? Its one of those things somewhere down my list to investigate.

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Old 17-08-2019, 23:49   #3
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Re: Raw water cooling trap

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Lucky, that could have cost you 7m of new hose as a minimum if run for a few moments longer.

How about an exhaust temperature alarm? Its one of those things somewhere down my list to investigate.

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Old 18-08-2019, 00:11   #4
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Re: Raw water cooling trap

A problem I have pondered on many times and have yet to come up with a good solution.
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Old 18-08-2019, 00:30   #5
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Re: Raw water cooling trap

Good catch - good ears!
I have (at times) considered putting a simple water flow meter/alarm in the raw water circuit - so far never got around to it.
I did fit a exhaust temp gauge and during testing, it would alarm after several minutes of running with a closed seacock. IIRC, I set the alarm point 4 or 5 degrees C of "normal".

I used the Engine Watch Dog - easy to fit. ENGINE WATCHDOG Audible Engine Overheating Alarm, Gauge & Sensor
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Old 18-08-2019, 01:16   #6
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Re: Raw water cooling trap

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Originally Posted by Wotname View Post
Good catch - good ears!
I have (at times) considered putting a simple water flow meter/alarm in the raw water circuit - so far never got around to it.
I did fit a exhaust temp gauge and during testing, it would alarm after several minutes of running with a closed seacock. IIRC, I set the alarm point 4 or 5 degrees C of "normal".

I used the Engine Watch Dog - easy to fit. ENGINE WATCHDOG Audible Engine Overheating Alarm, Gauge & Sensor
Interesting... what temperature did the exhaust alarm need to be set to?

... I'm having an idea...
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Old 18-08-2019, 01:21   #7
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Re: Raw water cooling trap

I just happen to have some spare picaxe chips and ds18b20 temperature sensors hanging around... I reckon I just strap the sensor to the exhaust somewhere near the water lift muffler on the output side. That would pick a temperature increase very easily.

I could just observe the recorded temperature under normal running conditions for a couple of days then program it accordingly. There's no way the wet exhaust hose gets even close to 100 degrees C in normal running, feels like about maybe 35 to 40 degrees when I think about it.
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Old 18-08-2019, 01:36   #8
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Re: Raw water cooling trap

We have a water flow alarm. It fires off long before any overheating occurs. It catches potential overheating problems before engine gets hot. https://www.aqualarm.net
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Old 18-08-2019, 01:51   #9
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Re: Raw water cooling trap

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We have a water flow alarm. It fires off long before any overheating occurs. It catches potential overheating problems before engine gets hot. https://www.aqualarm.net
Yes, that's a nice way to catch the problem early. I can make a temperature sensor out of bits I have spare already, so no cost to me, but I prefer the flow approach. Like you say, faster to spot problems.

I've put it on my wish list, the prices quoted are very reasonable. In the interim it's soldering iron time. I'll do the same as Wotname and test it by shutting down the cooling flow, just to make sure it works.
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Old 18-08-2019, 01:59   #10
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Re: Raw water cooling trap

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Interesting... what temperature did the exhaust alarm need to be set to?

... I'm having an idea...
Going on memory here - normal temp was around 35C and as the alarm is user set, I think I set to 40C initially. Later on I found the normal temperature was very stable under a variety of running conditions so I set the alarm point a bit lower (perhaps 38C).
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Old 18-08-2019, 02:28   #11
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Re: Raw water cooling trap

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Going on memory here - normal temp was around 35C and as the alarm is user set, I think I set to 40C initially. Later on I found the normal temperature was very stable under a variety of running conditions so I set the alarm point a bit lower (perhaps 38C).
Feels right, thank you. I'll rig a temperature probe and chip for the interim, until I can afford a fancy flow meter type, which do look pretty good.
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Old 18-08-2019, 03:38   #12
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Re: Raw water cooling trap

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Yes, that's a nice way to catch the problem early. I can make a temperature sensor out of bits I have spare already, so no cost to me, but I prefer the flow approach. Like you say, faster to spot problems.

I've put it on my wish list, the prices quoted are very reasonable. In the interim it's soldering iron time. I'll do the same as Wotname and test it by shutting down the cooling flow, just to make sure it works.
If you are familiar with a shuttle valve you could use a magnet in the shuttle to trigger a hall effect switch to hold the alarm off when the shuttle was pushed up near the HE switch. Loss of cooling water flow would allow the shuttle to sink away from the switch triggering the alarm.
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Old 18-08-2019, 04:30   #13
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Re: Raw water cooling trap

Interesting good idea water flow alarm
I did create a water pressure circuit to turn off my heat pump compressor if the cooling water flow quits, it turns off a contactor (big relay) instantly.
If water flow restarts, the compressor would come back on.

I used an analog GE 3 position washing machine water level switch. It is highly sensitive to water pressure. Its been working great. Prevents the head pressure of compressor from soaring to 400 psi and turning off. I have it set to the highest setting, and there is also an adjustment screw on top where you can modify it more.

The same type switch could be used on the raw water flow. Sound an alarm, or maybe turn off engine if you contrived a delay circuit. The switch has been very reliable.

PART# WH12X10065 was the one I used, but any analog 3 level washing machine switch will work. Analog switch typically has only 3 contacts, NO, NC, C.
Side of switch I used is NO and closes under pressure is the setup I used to connect relay. Terminal are all labeled on the switch.

You can even rig an indicator green light to show you have water pressure, and a red light and alarm when you don't.

With this on the heat pump, I dont even look at water flow, I just turn it on, if it comes on, I know the water is flowing.
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Old 18-08-2019, 04:53   #14
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Re: Raw water cooling trap

I am going to do the same thing for my generator. Detect water pressure off the raw water pump. Wred in series with the overheat temp cutoff switch.
My gen is an old MCCK very analog type machine so easy to do this.

I do not like the idea of a generator running with no one really paying attention to it, and then it overheats or burns the exhaust tube up or WORSE.

this switch is sensitive enough to detect water flow from a cranking water pump before it has started. Much less than a pound of pressure can click it off-on on the low setting.
I noticed it would detect (could feel switch click on and off) being raised or lowered when the tube was full of water on its lowest setting, so that must be very low pressure indeed.

My main engines, I would only setup as a light and alarm, if I did this.
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Old 18-08-2019, 04:56   #15
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Re: Raw water cooling trap

Quote:
Originally Posted by sdowney717 View Post
Interesting good idea water flow alarm
I did create a water pressure circuit to turn off my heat pump compressor if the cooling water flow quits, it turns off a contactor (big relay) instantly.
If water flow restarts, the compressor would come back on.

I used an analog GE 3 position washing machine water level switch. It is highly sensitive to water pressure. Its been working great. Prevents the head pressure of compressor from soaring to 400 psi and turning off. I have it set to the highest setting, and there is also an adjustment screw on top where you can modify it more.

The same type switch could be used on the raw water flow. Sound an alarm, or maybe turn off engine if you contrived a delay circuit. The switch has been very reliable.

PART# WH12X10065 was the one I used, but any analog 3 level washing machine switch will work. Analog switch typically has only 3 contacts, NO, NC, C.
Side of switch I used is NO and closes under pressure is the setup I used to connect relay. Terminal are all labeled on the switch.

You can even rig an indicator green light to show you have water pressure, and a red light and alarm when you don't.

With this on the heat pump, I dont even look at water flow, I just turn it on, if it comes on, I know the water is flowing.

Well.... Bugger! Seriously. That's really clever and just last week I THREW OUT a water level sensor from a LG washing machine from which I'd scavenged the direct drive motor for a generator.



But hey, that really IS clever.
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