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Topic: Loss of Coolant Alarm (Read 886 times) previous topic - next topic

Loss of Coolant Alarm

Special thank-you to Barndog-Rick and ProTech-Mike. . .

We wanted to prevent damaging our engine if a freeze-plug or coolant-hose let go, allowing all coolant to exit causing a disastrous engine failure.  One coolant loss engine damage for our Forum is one too many.

We now have a "Loss of Coolant Alarm" for our non-electronic Cummins C8.3.

Installed oil-pressure switch and pressure gauge with inside audible alarm when coolant system pressure is too low.  Thanks again Mike.

Our oil pressure switch of choice had FNPT-male DrySeal threads that are a little different than MPT-male.  F in 'FNPT' stands for 'Fuel' and is interchangeably called NPTF.  Sometimes F is used for Female (M for male) on standard NPT which only adds to the confusion about the uncommon DrySeal type.

I learned that NPTF thread roots are designed to interfere with crest of the mating thread, which creates a mechanical seal through thread form deformation at assembly and does not call for sealant at first use.

We did manage to get a leak-tight seal with the FNPT into a standard NPT Tee.  Motorhome's coolant pressure tank had a plugged NPT port and our meter also had NPT so it all fit together ok.

The oil-pressure switch has normally-closed contacts to which we wired a piezo-sounder.  The switch also has normally-open contacts to which we wired a LED.

Our test drive showed the N/C contacts open about 3 psi with an alarm below 3 psi.  The N/O contacts close about 5 psi turning on the LED indicating the coolant system is pressurized.  So while driving, no-sound with LED-on indicates all is normal.

There are many oil pressure switches available, with different mounting threads, some metric, various pressure settings, resistance and number & type of electrical contacts.

Our switch is Kemparts PS128 from RockAuto.com $1.43 + $2.99 shipping. 

Decided to add a pressure gauge to learn about our coolant system normal working pressures.  Gauge is Winters PEM136, 2", 0-15 psi, Amazon $7.49.


Re: Loss of Coolant Alarm

Reply #1 –
And here are switch and meter packaging . . .

Re: Loss of Coolant Alarm

Reply #2 –
Barry,

So, your alarm sounds until the engine/coolant is warm enough to generate 3 PSI of pressure in the cooling system?
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Loss of Coolant Alarm

Reply #3 –
Quote from: wolfe10 –
Barry,

So, your alarm sounds until the engine/coolant is warm enough to generate 3 PSI of pressure in the cooling system?
That is probably where the toggle switch comes in. Wait an see.
1999 40 ft. U-320 wtfe build 5563 Chuck & Lynda's "Rollin' Inn"  2030 watts solar
prev. mh's 71 GMC 5 yrs. 73 Pace Setter 1 yr. 78 Vogue 5 yrs 81 FTX 40ft all electric 18 yrs. 1996 Monaco Signature 3 yrs.
2014 Grand Cherokee Overland
Dream as if you will live forever. Live as if you will die today.  James Dean

Re: Loss of Coolant Alarm

Reply #4 –
Yes and Yes to alarm sounding until coolant warmed up with switch. 

But found that within a minute or so, coolant system pressure increases to turn alarm off, but takes a little longer to turn LED on.

This project was sort of trail blazing for me, with FNPT research, not knowing if FNPT inside NPT will leak, and not knowing how this oil pressure switch works, and not being sure of engine coolant psi.  So I sourced the 12v from a hot source, not ignition so I could watch results after engine shutdown.  As noted, I put a switch on the 12v so I could control the sound. 

BTW, having the LED turns out to be security, assuring that coolant system is sealed and pressurized.  And lets us know we did not forget to turn power switch on.  Many oil pressure switches are just N/C single contact to switch's threaded ground.

After finishing the plumbing part of the installation, the wiring side was not as polished, and over time may be enhanced with ignition source, but for now it is what it is.  Time to move on to installing a new Windows computer  and fixing a slow to let-down outside motorhome step.

Hope this idea can help another, and maybe Rick will add for his new engine.

Of  course, it is still not known if the alarm will save an engine, as will psi quickly drop to almost zero if a coolant hose lets go, and it takes a manual shutdown when alarm goes off.

Re: Loss of Coolant Alarm

Reply #5 –
Just wondering if my coach has a loss of coolant alarm. Is the sensor located on my fill tank?  How can I test the system to make sure it works?
John & Carm Morales

"We travel not to go anywhere, but to just go.  We travel for travel's sake.  Our great desire is to move."

Re: Loss of Coolant Alarm

Reply #6 –
Rigged up a similar oil pressure alarm on a Baja bug I built in the early 80's had a oil line rupture while passing a Sunday driver Corvette. Buzzer went off, killed the engine and coasted to a stop. Oil covered Vette owner was not happy, but settled for 10 bucks. Quite frankly, even though no drugs or booze was involved I don't recall how I got 45 miles back home.
Old Phart Phred, EIEIO
89 GV ored 36' #3405 300 hp cat 3208 ATAAC side radiator, mountain tamer exhaust brake

Re: Loss of Coolant Alarm

Reply #7 –
Thanks Barry...still counting my lucky stars that we have the same coach!
George and Steph
1997 U270 36 Build 5081 "Honu"
1180w Solar 400A lithium all Victron house system
Motorcade 17670, SKP 128300, FMCA F459019
73 VW Camper, 79 VW Camper, 2363 Sunline, and an Arctic Fox 25P

Re: Loss of Coolant Alarm

Reply #8 –
This is a cool idea, but of course I have to think up ways to make it more complicated.

Perhaps a 3 switch setup, coolant pressure, oil pressure, and engine temperature in series.  If the coolant pressure is under 3 PSI, and the oil pressure is over say 30 psi, and the engine temperature is over say 100 degrees, then the alarm sounds.  Minus any of the three, it stays silent.  That way if the engine is off and the ignition is on it stays silent.  If the engine is on but has not yet warmed up, it stays silent.  If the engine is on, and warmed up, but the coolant pressure is over 3 psi it stays silent.
Mike & Lilli
1991 GV U280 36' SBI, 3208 Cat, Build #3825
4320 Watts Solar
Kansas City, MO

Re: Loss of Coolant Alarm

Reply #9 –
Stop the Press. . .

Our coolant loss alarm with a pressure switch does not work.


See May 22 2018 topic,  "Forget Making a Coolant Leak Alarm"