Forget Making a Coolant Leak Alarm
As noted in our April 2018, "Loss of Coolant Alarm" posting, we were pleased that we installed a switch that will alarm if we have a major coolant leak, protecting us from a catastrophic engine failure.
A new pressure switch triggers the alarm if coolant system pressure falls below 3 psi. Initial testing around town showed the alarm idea is a practical inexpensive simple idea. After all, since our radiator cap opens at about 12 psi, it should be a problem if the sealed coolant system pressure falls below 3 psi.
WRONG...
We left San Diego heading east on I-8, drove up the mountain and while driving down the other side, the pressure alarm sounded off. This was our first highway drive since installing the alarm, and figured we have a coolant loss. After much examination and further driving we learned something new about coolant systems:
Driving up mountain caused engine to work harder, heating coolant, which expanded coolant, which increased system pressure above the radiator cap setting, which allowed coolant to leave flowing into overflow container.
We know that when the system cools, coolant 'shrinks' causing a vacuum that sucks fluid from overflow back to sealed coolant system.
With our wonderful over-size radiator & fans quickly removing heat, with engine load reduced, the pressure drops below radiator cap setting and the sealed system pressure quickly drops.
Moving coolant to overflow leaves less volume in sealed system, also lowering pressures. Coolant is not returned to system until pressures drop below zero and a vacuum is formed.
Who would think that with the water pump flowing coolant to remove engine heat that our internal coolant system pressures would mostly be very low. And only occasionally going over 3 psi. Seeing the overflow container fill, we knew that the system does reach 12 psi.
A well-designed coolant system maintains temperatures but at pressures from below zero psi to around 12 psi.
I tried to learn more about coolant system operating pressures, but could not find any meaningful info, other than radiator cap settings. And how increased pressure, increases the boiling point.
So, coolant system leaks cannot be measured by system pressures.
A coolant level sensor does protect computerized engines. But those of us without computers will have to find a way to measure levels if we want a coolant loss alarm.
Back when the Chevrolet Vega's were burning up from coolant loss they gave away a kit to sense the liquid level. Looks like some are still around
NOS 71-74 CHEVROLET VEGA LOW COOLANT LEVEL INSTALL KIT GM 364002 | eBay (https://www.ebay.com/itm/NOS-71-74-CHEVROLET-VEGA-LOW-COOLANT-LEVEL-INSTALL-KIT-GM-364002/351600457750?hash=item51dd053816:g:jd4AAOSwuMFUh1b9)
Barry,
You could use a Murphy L-150 or EL-150 switch gage. I have used them for years and they should still be made.
Mike
Yes, You have to have a 10 or 13# cap to keep the fluid in. 3-6# will not work with a 3# switch IMHO. Also if you release the pressure after start the light stays on.
Many Auto have an electrolysis /PH readers.
IE 1996 VW Golf has a probe that gets/gives a signal when covered. I can look at the FSM to see how it works if you want.
FWIW the Vega kits looks easy and cheaper.
Barry,check out the FW Murphy site like the above post mentions,low coolant shutdowns are common on just about every
stationary engine out there from generators to gas compressors,was going to mention it before but seemed like you wanted to make your own.
Looks to be a solid solution. Plentiful on ebay.
The Murphy level shutdowns are well made and will work within the radiator cap pressures.
We still have the analog pressure gauge in place , and days after engine is off, the system is so well sealed that ambient air temps, etc expand the coolant to around 6 psi without the engine running. It does vary.
Have not yet decided on what alternate coolant level sensor to use. Thanks for the recommendations.
We have the audible alarm off, but the LED still turns on at about 6 psi and above.