cooling system alarm

[Sangster21]

I am nearly finished with transom/stringer/deck replacement on my Sangster 21 project. I am planning the electrical re wire and am thinking that I would like to rig up some sort of alarm for the sea water side of the cooling system. Engine is I6 with MC1 outdrive. I don't know a lot about boats, but I do know it is common for the intakes on the leg to get covered up with kelp or refuse. There will be of course a temp sending unit in engine water jacket and a gauge in instrument panel. Good, but it would be nice to find out a cooling issue before an overheat occurs.
Can I plumb in a flow or pressure sensor/sender in the raw water line from the outdrive? I believe the unit is called a Hobbs pressure switch. Where would the best location be to install the unit? I think a buzzer or bell would be the best output for such a device. Any advice would be much appreciated.
Thanks
Alan

 

[HT32BSX115]

Re: cooling system alarm

Howdy up north!

I have been thinking about something similar. You'll want to put a low pressure gage on the raw water supply line from the transom (raw water pump) and measure the pressure range (Idle to full throttle) you have under normal operation.

You don't want the "tattle-tail" yelling at you when you're idling around.

I haven't measured mine but I am guessing somewhere around 10 psi at idle. Mercruiser uses a similar system for temp, oil pressure, and drive lubricant level all connected to the same "buzzer" using a common single wire circuit. I decided to wire mine to individual (labeled) lights.....doing it this way requires a wire for each sensor and light. and individual buzzers (which you can get at radio shack for a few dollars)

The current system just buzzes when any one (or more) of the three sensors detects a fault (or the single wire shorts someplace!)

Having a separate wire and llight/buzzer, identifies the problem immediately.

 

[Sangster21]

Re: cooling system alarm

Thanks for the reply HT32BSX115. Looking around the internet how about something like a 4lb normally closed switch. I would power it from the Run circuit of the ignition switch. Hopefully by the time the engine starts there is enough pressure to open the switch and you would only hear it if pressure drops below 4lbs. It could also function as a telltale for leaving the ignition on after shut down. Sound OK?
Thanks
Alan

 

[Don S]

Re: cooling system alarm

At idle, you will be lucky to see 1 or 2 lbs of pressure with those pumps. Just not enough output of the pump at idle with the flow of water out of the engine to really build up much pressure. You would need a sender that shows flow, not pressure.
All the newer engines just use a temp switch that goes off when the engine gets around 200 to 210 degrees.

 

[Sangster21]

Re: cooling system alarm

OK good to know. Thanks Don. Any idea if there is such a thing as a flow sender/switch?
Alan

 

[Don S]

Re: cooling system alarm

https://www.aqualarm.net/comerus/store/comersus_listItems.asp?idCategory=67

http://aqualarm.net/datasheets/save_your_engine_kit_one_inch_to_one_and_one-half_inch.pdf

 

[Sangster21]

Re: cooling system alarm

Ta Da!! Looks great, thank you Don. To me this looks like a smart thing to incorporate into a system. I imagine this could also indicate when an impellor was getting tired as flow would reduce particularly at low RPM. Cool.
Alan

 

[achris]

Re: cooling system alarm

The current MPI engines use a pressure sensor in the incoming water line. It's signal is fed to the ECU and if the pressure drops too low the alarm fires.... (I thought of doing this back in the late 80's but never got around to actually doing something about it) This is a sensor, not a switch and is only useful for running a gauge, but it could be useful for you...

The part number for the pressure sensor is -881879010... He's no cheap cap't....

Chris.........

Next time I have the boat out I'll take the laptop with me and let you know what the pressure readings are from idle to WOT....

 

[achris]

Re: cooling system alarm

Ta Da!! Looks great, thank you Don. To me this looks like a smart thing to incorporate into a system. I imagine this could also indicate when an impeller was getting tired as flow would reduce particularly at low RPM. Cool.
Alan

And when the elbow or manifold is starting to block up, as the pressure will rise.

Chris.....