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.