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The missing coolant gauge

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TL;DR: It's time for us to make a gauge to monitor our coolant recovery tank level and let us know as soon as the levels indicate a leak or air incursion into the cooling system. Here's an article on different ways to measure coolant level. Let's noodle on how to do this, and build the missing coolant gauge. Below is a discussion of what the coolant tank does, how the level changes, and why this guage is important.


One of the insidious issues that seems to be emerging with this car are coolant leaks. We had a rash of reports lately. The leaks are small, weeping from the coolant block, old radiators, etc. The problem is that it seems that you can lose quite a bit of coolant, to the point where there is air in the head and it needs to be burped. The coolant temperature gauge is noted for being insensitive, so this can go unnoticed. Finally, there is a theory that a cylinder head with air in it can lead to overheated cam bearings, galling and eventual seizure and snapping of the camshaft - at least, that is one theory about camshaft failure. It seems that no one will be immune to this - they seem to be an eventuality, can go unnoticed, and potentially result in the end of an Insight's life.

The thing is, you can get advanced warning of this simply by checking the coolant recovery tank. This is not some "boilover" or arbitrary tank - it actually is a simple, clever but necessary piece of engineering. It's purpose is to permit a cooling system to be almost completely free of air and completely sealed.

The problem with a sealed system is that the coolant and any residual air expands as the temperature rises and contracts as the temperature falls. For an example of this, don some oven mitts and pour an ounce or two of boiling water into a coke bottle, swish it around for a few seconds, dump it out and quickly cap the bottle. Within a few seconds the hot air inside will cool and by the time it has reached room temperature, the bottle has collapsed.

The same problem happens in a sealed cooling system. What the overflow tank does, then, is when the engine gets hot, the little bit of trapped air expands, as does the coolant to a much lesser extent. The trapped air increases in pressure. Eventually the pressure opens a valve in the radiator cap and coolant in the radiator is pushed into the overflow tank. That's why it's good to put a sticker on the overflow tank and mark the level when it's hot - it's going to be highest when the engine is hottest and that air pocket has expanded the most.

As the engine cools the pressure drops as the air takes up less space and sucks in coolant from the expansion tank, like sucking soda from a straw. That's why it is SO IMPORTANT to make sure that straw is attached and well-secured and there is no leak where it attaches to the cap. I have seen and read about several of these fallen off and when they do, only air gets sucked in and since air expands much more than coolant, next time around a lot more coolant is pushed into the tank! Anyhow, when the engine is coolest the pocket is smallest and the most coolant has been pulled back into the car and a second mark is placed on the tape.

This is also why if you ever find that tank empty, GULP! the cooling system is sucking in air! Refilling it is not enough - Time to burp the car!

With the two marks we can now see the range of coolant being drawn into and out of the car on each cycle. But what a PITA to lift the hood and check the tank every time you start and finish a drive to check those two levels, especially when the high and low points change very little over months of driving! What we need is a something to do this automatically, that makes sure that the coolant never goes too low when cold, too high when hot, and that the distance between high and low does not grow too large, indicating an incursion of air in the system.

I've put an order into Amazon for some stuff that I think will work, but before I discuss it here, let's see what ideas people can come up with for measuring and reporting the coolant recovery tank level.
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· Linsight Designer
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I'd recommend a capacitive liquid level sensor. No moving parts. Unless the tank gets too full or empty, you'd only need to log the delta between keyON and keyOFF.
 

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Discussion Starter · #3 ·
I'd recommend a capacitive liquid level sensor. No moving parts. Unless the tank gets too full or empty, you'd only need to log the delta between keyON and keyOFF.
Yes, the capacitive method looks quite interesting. I will have to look at some circuits and try some experiments. I suppose the simplest approach would be to put the cap into an oscillator circuit, use sufficiently fast Arduino or whatever to sample it and take an FFT.

So what I bought on Amazon was a module with a VL6180 time of flight distance sensor for about $12. I found a $15 ovreflow tank on eBay so I figured I would drill a hole in the top for the sensor. Of course, the TOF sensor will get filthy. In that respect the capacitive sensor has more promise.

Agreeed on key measurements being at key on and key off to determine if air has entered, with periodic measurements in case of other issues.

I realized that sensing is probably not the hard part. For presentation, one of those tiny narrow displays would be pretty neat; show the high and low levels and where the car is. But where to put it?
 

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Interesting idea.

Are we trying to resolve/ascertain the level of the liquid at all times or just sense when it goes above max or below minimum.

I would say just when high/low and a simple beeper.

I suggest drill two holes in expansion tank just above and below high/low marks and fit two of these sensors.
(See attached pdf)


Minimal electronics. 12v supply, piezo beeper and maybe a latch as the sensors can switch ~100ma .
 

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Discussion Starter · #6 ·
I suppose the simplest approach would be to put the cap into an oscillator circuit, use sufficiently fast Arduino or whatever to sample it and take an FFT.
Or not... measuring capacitor charge time would be simpler. but...
it needs to fit in the hole. A 3D printed holder would maintain plate separation. I used this Google-sourced arbitrary calculator to calculate the capacitance of two plates a mm apart (maybe that's too close?) with 2 sq inch area. Comes out to 10 pF. Capacitance Calculator

and with a 100K resistor the time constant is 1 ms. Which requires a sampling rate that's quite high. The ADC in the AVR128DA28 apparently can do 130Ksps so maybe that can handle it.

The optical solution seems simpler from a programming and mechanical engineering perspective compared to the capacitive solution. I have not thought about conductivity of the coolant and the possible need to waterproof the plates.

I don't see any reason to add a display... maybe just add a beeper, or you could add it as I/O to Pegasus.
Definitely Peter's solution would be most compatible with an indicator. If you can't show trend information there's no point in collecting it.

I want a display because I would like to know trend information, so the capacitance and optical methods are in the game for my car. It will tell me whether a leak is sudden and I need to deal with it right away or has been progressing slowly over some time.

Of course, I could log to an SD card and write a small app to examine the log on the PC when the idiot light comes on.
I suggest drill two holes in expansion tank just above and below high/low marks and fit two of these sensors.
Well those seem like the simplest solution for 90% of users. I personally want to know how much the level swings between cold and hot which tells me how much air is in the system (actually, I need to test that theory by intentionally introducing a fixed amount of air into the head.)

Problem is that you have to figure out how to put the nut on from inside the tank! I can barely reach the high level with one finger only. If only you could put the nut on from the wire side. Then just fish the wire through the hole and tighten the nut from the outside.

Also, $30 each, but still, better than nothing. So does a competitor make one in the style needed?

OR maybe just get a bunch of panel mount LED holders, seal them internally with HondaBond HT, make a small gasket, and using infrared LEDs/photodiode, just build your own, kind of like how a remote control works. Look for a change in signal level.

I found these small float switches but one wonders how long they will last constantly moving in a car, and not sure if there is a place to install them with enough clearance. Still, I ordered a few to add to the water heater leak catch pans in my house:

https://www.amazon.com/Anndason-Pie...ref=pd_day0fbt_img_sccl_2/132-0313008-5727233

This is the tank I bought on eBay for experimenting:
19101PHM000 HO3014127 New Coolant Reservoir For Honda Insight 2006 2005 2004 | eBay
I suppose stock of these is not unlimited.
 

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Discussion Starter · #7 ·
The distance sensors and another coolant reservoir arrived.
Font Telephone Office equipment Wood Gas


Hand Gadget Nail Font Electronic device

Above: likely will drill hole under sensor and coat everything with HondaBond. Actually could use a suggestion for a conformal coat spray.

Might use a float switch as a backup. Yeah. That's a good idea.
 

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What about putting the tank inside the car to visually monitor it? 😀
A coolant pressure drop warning could be useful too. Like if a hose bursts or pops off.
 
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y2k silver'sight, hch1 5spd, snow tires
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What about putting the tank inside the car to visually monitor it? 😀
A coolant pressure drop warning could be useful too. Like if a hose bursts or pops off.
i laugh because when i first read this thread the relocate coolant tank to cabin crossed my mind, i can use every bit of heat in there that i can get for the next few months.
i really like the pressure sensor idea, could be useful in diagnosing a blown head gasket (over pressure) condition as well as a low-pressure condition(y)
 

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Discussion Starter · #10 ·
What about putting the tank inside the car to visually monitor it? 😀
A coolant pressure drop warning could be useful too. Like if a hose bursts or pops off.
I did pick up some strain gauges that are very tiny. Perhaps the rubber cap on the bleed tube flexes enough under pressure to warrant glueing a strain gauge onto it. We are only looking for a sudden change from pressurized to not.
 

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y2k silver'sight, hch1 5spd, snow tires
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I did pick up some strain gauges that are very tiny. Perhaps the rubber cap on the bleed tube flexes enough under pressure to warrant glueing a strain gauge onto it. We are only looking for a sudden change from pressurized to not.
hey you should pull out the bleeder next to that tube and measure the threads, might be easy to adapt a sender in that location
 

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another simple solution would be to glue a bimetal 'snap switch' like the ones they use to turn on the electric fans without a cpu, could wire it to the door buzzer circuit
 

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Discussion Starter · #13 ·
hey you should pull out the bleeder next to that tube and measure the threads, might be easy to adapt a sender in that location
That's a great idea; the sensor should read pressure or vacuum to whatever the radiator cap specs are x2. However, gotta leave that project to someone else, the mechanical part at least. If someone can identify the hardware, the Arduino code will be easy. The only concern is that this sensor now becomes a new point of failure. A cheap sensor that breaks can cause the very loss of pressure that is being monitored for.
 
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