Coolant Level Sensor

[Pjf]

Gday,
I'm hoping you guys can give me a hand here, I'm trying to diy a coolant level sensor for my 4wd, and this is what I've got so far, just using a normal T5 dash light bulb and a buzzer, also using a WS-03 water level sensor.

Specs
Bulb
T5 12V 1.2W

Buzzer
Hyt-3015D
Voltage : 8-15V
Current : 15mA

WS-03
Working voltage: DC5~24V
Output current: 300mA
Response time: 30 seconds
Output voltage: 0.5V
Current consumption: 5mA

Any help would be greatly appreciated.

[BrokenYugo]

Should be powered from the key on power, not directly off the battery.

[Pjf]

Yes it will be, I've just simplified it for the purposes of this diagram.

[Benta]

From what I see, it's only capable of sensing the level in the reservoir, not the cooling system. The reservoir is normally semi-transparent, so a short glance under the hood is enough.
Useless to my mind, but it's your money.
Coolant temperature is much more important for engine health monitoring.

[james_s]

From what I see, it's only capable of sensing the level in the reservoir, not the cooling system. The reservoir is normally semi-transparent, so a short glance under the hood is enough.
Useless to my mind, but it's your money.
Coolant temperature is much more important for engine health monitoring.

Looking at the reservoir requires stopping the car, getting out, popping the hood and taking a look, how often do you think most people do that? If you have a hose failure or other serious leak that dumps your coolant you're not going to know until the car already starts to overheat, and that assumes you notice the gauge in time (like my brother didn't). Coolant temperature is indeed the critical factor, but a warning that the level in the expansion reservoir is low would be very useful to provide an early warning.

Personally I think all cars should have an obnoxious audible warning buzzer for both high coolant temperature and low oil pressure but I've never seen one that did.

[Benta]

I said it was her/his money.
If soneone likes to stick alarms, lights, blaring horns, beepers and so on all over the car; well, it's a free world.
I only said I find it useless. That's a personal opinion, nothing else. And which is why I drive a '97 stock Miata. No nanny gimmicks.

[Pjf]

My car is a Japanese import (Delica) that has a pressurized expansion header tank, by the time you see any temp change, it's usually too late, they are also very prone to killing cylinder heads with the slightest overheat, so no not a waste in time and effort.

EDIT: this is also the 2nd time I've had to replace the head, so honestly it's cheap insurance.

[Pjf]

Ok, moving on, from what I've been looking at I can do what I'm wanting with a mosfet, and I'm guessing n channel, but beyond that I'm clueless, so if you guys could advise me if my diagram is correct and will work, also what mosfet would do the job for me, thanks again.

[james_s]

I said it was her/his money.
If soneone likes to stick alarms, lights, blaring horns, beepers and so on all over the car; well, it's a free world.
I only said I find it useless. That's a personal opinion, nothing else. And which is why I drive a '97 stock Miata. No nanny gimmicks.

That seems like an awfully negative attitude. I also drive an old car, 1990 in my case and I think modern cars have far too many useless gadgets, however even my car has a warning light for low brake fluid and low window washer fluid but there isn't one for low coolant. Personally I think a simple indicator light to warn you that critical fluids like engine oil and coolant is far from a useless gimmick and an alarm horn that goes off at the point that engine destruction is imminent if not shut down immediately seems like another good idea. I mean it's not as if it would cost much, and it really should never trigger. It's a bit like a smoke alarm, it will just quietly sit there until there is a *really* good reason to get your attention. Coolant temperature and oil pressure alarms are nearly ubiquitous on marine engines so it has always seemed strange to me that I've never seen one on a car. I have seen several engines damaged due to overheating and I once overheated one of my cars when a heater hose burst and dumped the coolant, I had no warning and it was just luck that I happened to glance down at the temperature gauge in time. It only takes once to end up with a repair bill in excess of the value of the car.

[james_s]

Ok, moving on, from what I've been looking at I can do what I'm wanting with a mosfet, and I'm guessing n channel, but beyond that I'm clueless, so if you guys could advise me if my diagram is correct and will work, also what mosfet would do the job for me, thanks again.

While I'm not familiar with the sensor you're using, that looks like it ought to work. The mosfet is not critical at all, whatever you have on hand or can salvage from something will be fine. If you're going to buy one I'd probably look at something like the 2N7000, but any bog standard power mosfet like the IRF730 would work too, though massively overkill.

Do you have the sensor already? Why don't you lash something up on the bench and try it out?

[Pjf]

Ok, moving on, from what I've been looking at I can do what I'm wanting with a mosfet, and I'm guessing n channel, but beyond that I'm clueless, so if you guys could advise me if my diagram is correct and will work, also what mosfet would do the job for me, thanks again.

While I'm not familiar with the sensor you're using, that looks like it ought to work. The mosfet is not critical at all, whatever you have on hand or can salvage from something will be fine. If you're going to buy one I'd probably look at something like the 2N7000, but any bog standard power mosfet like the IRF730 would work too, though massively overkill.

Do you have the sensor already? Why don't you lash something up on the bench and try it out?

Thanks, yes unfortunately I have to buy, and with no electronic stores in my city, I have to rely on ordering over the net, with a lengthy wait. I've ordered a handful of the 2N7000's, hopefully this should get me up and running, Thanks again. 

[Mechatrommer]

and I think modern cars have far too many useful gadgets, however even my car has a warning light for low brake fluid and low window washer fluid but there isn't one for low coolant.

i dont think the low to middle class cars even today have such fancy features, its not even guaranteed in high class one, it is still not a common practice/standard/requirement i think. at least i wish i have beeps warning when coolant reached slightly above the thermostat setting, or in between before it reaches dangerous 100degC. we dont usually look at the temp warning light on the meter. so the old habit still apply.. open the hood and check everything, top up whats needed. check tyres pressure etc before a long miles journey. if we want automated everything, just checking coolant level will not guaranteed smooth ride, but at least its one little step to a bigger one. btw, to OP, lack of information provided, such as what voltage/current reading is yellow wire in TC-03 when submerged and when not? i tend to use active device such as comparator or opamp to check the condition, cannot suggest a circuit since lack of sensor information. using mosfet probably needs careful biasing. ymmv.

[mikerj]

The WS-03 has a working temperature range of 0-60C according to this which doesn't seem adequate for automotive use.  A header tank will easily get hotter than that under normal use.

[james_s]

i dont think the low to middle class cars even today have such fancy features, its not even guaranteed in high class one, it is still not a common practice/standard/requirement i think. at least i wish i have beeps warning when coolant reached slightly above the thermostat setting, or in between before it reaches dangerous 100degC. we dont usually look at the temp warning light on the meter. so the old habit still apply.. open the hood and check everything, top up whats needed. check tyres pressure etc before a long miles journey. if we want automated everything, just checking coolant level will not guaranteed smooth ride, but at least its one little step to a bigger one. btw, to OP, lack of information provided, such as what voltage/current reading is yellow wire in TC-03 when submerged and when not? i tend to use active device such as comparator or opamp to check the condition, cannot suggest a circuit since lack of sensor information. using mosfet probably needs careful biasing. ymmv.

We're a group of engineers and other technical people so the percentage of us that checks under the hood of our cars periodically is probably higher than average, but I think even here many would admit to not doing it as diligently as they should, and in a case like mine where a hose burst while I was driving it wouldn't have done any good to have checked the coolant before I got in my car and drove away, things can go from perfectly fine to causing serious damage in a matter of minutes. I don't think most ordinary people ever check stuff on their car anmore. I would wager that probably 25% of drivers don't even know how to pop the hood. Modern cars are very reliable compared to how it was prior to the last 30 years or so, while trivial for people like us, I don't think it's reasonable to expect most people to do that now.

[SmallCog]

I think there may be a few posters here from quite "developed" countries who don't comprehend the issue at hand.

People have died from being stranded in the outback by being bogged, or mechanical faults like an overheating engine. Catch the fault early you stand a chance of repairing it, continuing your journey, and finishing it safely. Catch that fault too late and you're in the middle of nowhere with potentially nobody driving past for days/weeks.

Even if you survive and are rescued the cost to recover a broken down vehicle a few days drive into the bush can far outweigh its value. It's not like the "auto club" will just turn up with a tow truck in 30-45min.

Australia is a very big, very empty, and in many places very inhospitable continent. Alarms for things like low coolant levels are a good idea and quite common.

OP I think you're on a the right track with your plans, good on you for having a go at DIYing it

[floobydust]

OP I think you're on the right track.
Older vehicles have their coolant recovery bottle at atmospheric pressure, and only drain into the radiator to top up as the engine cools and creates a small vacuum. You don't know it's low until morning after.
Modern vehicles have their coolant recovery bottle at system pressure, which reflects the coolant level. So that could work here.

I would say your scheme could flicker and false trigger due to sloshing. It's customary to have a long 30 second delay circuit to prevent this.
Luxury cars with a low coolant sensor, I have only seen a brass electrode in the radiator and even then, low coolant can still slosh and spray if the electrode is in the flow. It's a bit of a challenge because (in the cooling system) low coolant still surges, burps and splashes etc. My old Chevy temperature gauge would read fine when almost empty! Sensor was in the thermostat housing and I found low coolant meant the sensor never got wet... I had to move the temp sensor lower, into the cylinder head port (5.7L V8) and then it would finally read hot with low coolant.

The WS-03 water sensor, looks it has an open-collector output which means it needs a pullup resistor to turn on a mosfet, same as what you are doing and like fish tank circuit here: https://www.eevblog.com/forum/beginners/water-level-sensor-auto-to-up/
Same thing you are doing on a Fiesta, but no extra mosfet: https://www.fiestafaction.com/threads/diy-15-low-coolant-light-no-hacking-required.56722/

To your circuit, I would add a 2A fuse and series diode 1N4004 on power to prevent reverse spikes from damaging the sensor. 2N7000K mosfet I use, it has extra surge protection built-in. BS170 but add a 15V gate zener protection. Or upsize to a TO-220 size mosfet. There's a lot of semiconductor shortages going on right now and the perfect part is not always available. If you want I can sketch the circuit.

[jmelson]

Looking at the reservoir requires stopping the car, getting out, popping the hood and taking a look, how often do you think most people do that? If you have a hose failure or other serious leak that dumps your coolant you're not going to know until the car already starts to overheat, and that assumes you notice the gauge in time (like my brother didn't). Coolant temperature is indeed the critical factor, but a warning that the level in the expansion reservoir is low would be very useful to provide an early warning.

The way the coolant recovery bottles work is that when the engine is shut off, a vacuum is created that draws coolant back from the bottle to refill the radiator.  If a hose breaks or there is another large leak, the level in the recovery bottle will NOT drop!
So, you will get no warning from that system.
Jon

[Mechatrommer]

If a hose breaks or there is another large leak, the level in the recovery bottle will NOT drop!
So, you will get no warning from that system.Jon

hose will not break in 5 years or so time. we dont have to check the hose every now and then. if you argue like that, then nothing in the hood got any point at all, since temperature sensor can break too, wiring etc..

[IDEngineer]

If it's critical, just put a sensor in a primary hose somewhere and skip the tank. What matters is if you have fluid in the system, not the tank.

[floobydust]

Pic from the Ford Fiesta forum, looks like it's proven and works well enough.
OP, I would use this schematic as a start. It's not perfect and missing bigger surge protection (zener diode). The extra 1N4004 diode stops -ve spikes from damaging things, the most common problem in vehicle electrical systems.
Note I see different 2N7000 pinouts depending on the manufacturer, and the Wiki page so double-check.

[MikeK]

From what I see, it's only capable of sensing the level in the reservoir, not the cooling system.

Sorry if this seems like I'm "piling on".  I'm not.  But you may not be aware that the coolant reservoir in many cars (yeah, maybe not yours) *is* part of the cooling system and its level will vary in use.  Old style systems took advantage of pressure and [partial] vacuum to both allow coolant to overflow into the reservoir and to draw it back into the cooling system.  My 1990 Mazda Miata is like this.  The reservoir is unpressurized.  VW has been using the coolant reservoir as part of coolant cycling for decades.  My 1986 and 1991 VW Golf were like this...the reservoir was pressurized and had inflow and outflow ports for coolant cycling.  Coolant "low" sensor was implemented in the Golf sometime after 1986.

[SmallCog]

If it's critical, just put a sensor in a primary hose somewhere and skip the tank. What matters is if you have fluid in the system, not the tank.

I missed that it's going in the overflow bottle

The ones I'm familiar with go in the top radiator hose

https://daviescraig.com.au/product/low-coolant-level-alarm-kit-12-24v-1035

[floobydust]

Part of it is the nature of cooling system leaks- small ones, those that show up when the engine is cool, others when it's hot and pressured up.
I've experienced them all lol. Waterpump seals are the worst to track down. It's the catastrophic big leaks or little ones going on for months that are most dangerous.

In-tank sensors are capacitive, conductance, float reed switch with magnet. Lots of youtube videos on replacing float switch ones, moving parts- yuck. I guess they aren't that reliable and some people have really dirty tanks and electrodes get gummed up too. I recommend using the pressure washer at the local car wash to blast out the slime every 10 years, worked great.

[floobydust]

The ones I'm familiar with go in the top radiator hose
https://daviescraig.com.au/product/low-coolant-level-alarm-kit-12-24v-1035

Uh it's a float-based system, moving parts and yuck I don't like reed switches getting temperature cycled. And it's $228 OUCH. A model T could use a float sensor.
Capacitive level sensing is superior - no moving parts, nothing in contact with the fluid. But it needs more sophisticated electronics and firmware.

[james_s]

OP I think you're on the right track.
Older vehicles have their coolant recovery bottle at atmospheric pressure, and only drain into the radiator to top up as the engine cools and creates a small vacuum. You don't know it's low until morning after.
Modern vehicles have their coolant recovery bottle at system pressure, which reflects the coolant level. So that could work here.

I'm not sure what definition of "modern" you're using but I have a 40 year old car that has the coolant reservoir pressurized. I'm not sure how you'd have it any other way unless you had a checkvalve, the plastic bottle connects directly to the radiator via a length of rubber hose so the pressure in it is the same as in the rest of the cooling system.

[james_s]

Uh it's a float-based system, moving parts and yuck I don't like reed switches getting temperature cycled. And it's $228 OUCH. A model T could use a float sensor.
Capacitive level sensing is superior - no moving parts, nothing in contact with the fluid. But it needs more sophisticated electronics and firmware.

Capacitive sensing may be superior, but millions of cars on the road have float based liquid level sensors for various fluids, they work fine.

[static333]

To me, an overflow bottle sensor would be useless. I have a 1993 Mazda B2200 pickup. A packrat chew through a small water hose, supplying the intake manifold. Drove off and overheated. Collant level in the overflow bottle was normal as my system is not pressurized. Temperature gauge indicated only a slight temp. rise. Now I am checking the coolant level in my radiator each time before driving off. Looking into placing a temp sensor or a radiator-fan switch directly on the cylinder head, not into the coolant.

[floobydust]

I'm not sure what definition of "modern" you're using but I have a 40 year old car that has the coolant reservoir pressurized. I'm not sure how you'd have it any other way unless you had a checkvalve, the plastic bottle connects directly to the radiator via a length of rubber hose so the pressure in it is the same as in the rest of the cooling system.

The check valve is the radiator cap, it seals against 7-14PSI but not against vacuum.
I think the change came with plastics being able to withstand say 21PSI, or maybe it was safety.
Classic Chevy from the 1960's coolant recovery bottle was an option, more like an expansion tank connected to the radiator cap pressure relief port. It was for farm trucks that would overheat and people didn't want to lose glycol. See Model T erupt like a geyser when they overheat.
Otherwise, the radiator cap pressure relief port hose drained onto the ground, no recovery bottle at all until around 1972 it became standard equipment. It might also be due to cross-flow radiators (no tanks on top), vehicle emissions control causing engines to run hotter, in the 70's.
Safety issue is if glycol gets on the windshield, it just smears with the windshield wipers and you can't see much of the road if it boils over in a messy way.
Lots of Toyota's under 40 years old have coolant recovery units, but unpressurized. It seems to vary with car manufacturer's mindset.

Capacitive sensing may be superior, but millions of cars on the road have float based liquid level sensors for various fluids, they work fine.

Not according to the many Youtube videos, and most float sensors are embedded in the tank - non-servicable. A moving part in hot glycol mix with vibration and sloshing, add some dirt and oil - and it looks like all sensors are problematic. New vehicles are using capacitive probes, non-contacting with the fluid, no need for a cable-gland to run wires out of a pressurized compartment. Dodge RAM uses a reed switch inside a pressure well, with a float+magnet.
The sensors using electrodes seem to not work well either, Audi/Volkwagen expensive to change the tank. The probe resistance seems to be poorly engineered and of course the whole assembly has to be replaced, even if you only had a dirty electrode.

[Mechatrommer]

To me, an overflow bottle sensor would be useless. I have a 1993 Mazda B2200 pickup. A packrat chew through a small water hose, supplying the intake manifold. Drove off and overheated. Collant level in the overflow bottle was normal as my system is not pressurized. Temperature gauge indicated only a slight temp. rise. Now I am checking the coolant level in my radiator each time before driving off. Looking into placing a temp sensor or a radiator-fan switch directly on the cylinder head, not into the coolant.

its time to do major check... water pump dead? coolant leaking somewhere? indicated by level drop in radiator? find the leak! pray its not into cylinder block. if it is, major overhaul, fun! i never heard a car that will tell you "mr! you need to change top gasket! your water pump is busted! mr! i'm leaking badly!" the best i encountered so far is alphard 2018 model which will tell you to break for coffee if you drive more than X hours straight. which i think pretty stupid (i know when to take a break)

[darkspr1te]

I few idea's here.
In my old landrover i used a ULM2003/8 to create a led based water level sensor, the device uses the liquid to act as a switch on the ulm2003 and will trigger the ground side based on level of water.
The other trick i have used is a ultrasonic send/rec pair inside a tube, the tube stops the liquid from moving too much from the sensors location , that device was sold by a Ukrainian company called Escorts  or Digital Escort.

There also capacitive fluid sensors which should also work.

darkspr1te

[Circlotron]

Maybe a useful addition would be a water pressure sensor. Once the system is hot a burst hose would drop the pressure from several psi to zero very quickly, even before all the water has been lost and temp starts to rise. It would need to be disabled until the temp (and consequent pressure) initially rose to a certain minimum value.

[floobydust]

Low coolant sensing is still required for solar and electric car/battery banks. It seems to be all about price-point," here engineer you've got $1 to come up with something".
Tesla low coolant sensor is a lowly float/reed switch. Powerpack uses the same coolant recovery bottle/sensor as the cars. But no vibration in the Powerpack.

Interesting to note coolant contains about 5% corrosion inhibitors, defoamers, and along with the rubber, lime, calcium, metal dust, oil - this might clog a float/cover electrodes.

Pressure doesn't say much about low coolant level - where does the pressure come from anyhow? It's worth pondering... It only jumps up when it boils over.

[james_s]

Ordinary water/glycol cooling systems are pressurized, they run at somewhat higher than atmospheric pressure at normal operating temperature, it is done to increase the boiling point of the coolant. I agree though that monitoring pressure is not very useful, the simplest way to get the earliest warning is to monitor the level in the expansion reservoir. This way whether the leak is slow or catastrophic, you will be warned at the earliest possible point, when the reservoir is low but the engine is still filled with coolant. Float sensor with a magnet and reed switch or hall sensor will work. Optical sensor with LED and phototransistor is an option. Capacitive could work, maybe ultrasonic, even bare electrodes may be workable. It all depends on budget and mechanical constraints.

[BrokenYugo]

If it has an unpressurized reservoir, there are failure modes you won't catch looking at it, like a bad radiator cap (dirt common failure) or overflow hose, or a hose blowout if you miss the giant steam cloud.


If you're looking for max reliability, make an inspection checklist and pop the hood often, treat it like an aircraft.

[SmallCog]

even bare electrodes may be workable.

Another product here in Australia from quite a reputable manufacturer uses electrodes.

They make a point of the sensing being AC to prevent corrosion

https://www.redarc.com.au/images/uploaded/FLYER6-4%20-%207263%20LCA1224%20Coolant%20alarm%20ANZ%20brochure%20220128%20LR.pdf

Before choosing to monitor the tank it's essential to understand how the system functions. There are current model vehicles here in the carpark at work that have the traditional unpressurised overflow bottle. The level of these bottles (probably) wont change if you have a fault as they rely on a vacuum being created as the cooling system cools down to draw the fluid in.

[Circlotron]

Before choosing to monitor the tank it's essential to understand how the system functions. There are current model vehicles here in the carpark at work that have the traditional unpressurised overflow bottle. The level of these bottles (probably) wont change if you have a fault as they rely on a vacuum being created as the cooling system cools down to draw the fluid in.

Good example is son's '98 Camry that has plastic top and bottom radiator tanks. The top tank developed a small crack next to an integral mounting bracket and as a result it did not draw coolant in from the expansion tank because of the air leak. The overflow tank level looked normal but the radiator was way down.

[Pjf]

Gday, been busy the last couple of days, have some pieces on order, will update you guys once they arrive and I test some things out.

To many of the detractors who keep saying that this wont work because of it being an overflow tank, the car I'm installing it on doesn't have an overflow tank, it has a pressurized header tank, that is an integrated part of the cooling system(see attached picture.)


I've spent enough money on this car recently that a simple diy coolant alarm is quite frankly cheap insurance, considering last time I lost coolant, temp gauges showed nothing at all, it was only when I started to smell coolant after winding down a window that I noticed something up, by then it was too late, when this happened I had factory and aftermarket temp gauges, both of those didn't read any different until AFTER I pulled over. Now I've got the factory temp gauge, aftermarket temp gauge, engine watchdog and I'll have this alarm as well, once this is installed, it won't be obvious, it will be invisible until it goes off.

for those not in the know an engine watchdog monitors block or head temp directly with a bolt on thermocouple.

[SmallCog]

Gday, been busy the last couple of days, have some pieces on order, will update you guys once they arrive and I test some things out.

To many of the detractors who keep saying that this wont work because of it being an overflow tank, the car I'm installing it on doesn't have an overflow tank, it has a pressurized header tank, that is an integrated part of the cooling system(see attached picture.)
(Attachment Link)

I've spent enough money on this car recently that a simple diy coolant alarm is quite frankly cheap insurance, considering last time I lost coolant, temp gauges showed nothing at all, it was only when I started to smell coolant after winding down a window that I noticed something up, by then it was too late, when this happened I had factory and aftermarket temp gauges, both of those didn't read any different until AFTER I pulled over. Now I've got the factory temp gauge, aftermarket temp gauge, engine watchdog and I'll have this alarm as well, once this is installed, it won't be obvious, it will be invisible until it goes off.

for those not in the know an engine watchdog monitors block or head temp directly with a bolt on thermocouple.

You need one of these too, sounds like you're a collector! :-)

https://www.aisat.com.au/our-products/commercial/murphy-switch-gauge/murphy-20-series/murphy-basic-temperature-gauge/