Low Coolant Sender Unit

[DamirGTI 325]

Can someone enlighten me please , burnt my brain last night a bit - how this thing senses liquid level inside the expansion bottle ?!

 

Mine hasn't been working since i bought the car , i've checked the sensor wiring circuit and all seems fine , bulb on the instrument cluster works as well , then i cleaned up the sender a few times and tried testing it with a multimeter by immersing it in the bucket of water , results where as follows → zero Ohms , zero K ohms , zero volts , zero millivolts … i simply couldn't get any readings from the unit .. so i decided to , well , look what's inside the damn thing

 

Contains :

 

 

Main sender connector (ignore the black soldered wire , that one was just for a test) :

 

 

Float with steel ring on top :

 

 

.. and , this is interesting , “some sort of green stuff/tingy” ! :

 

 

 

 

 

Anyway , entire sender wiring bit + “the green thingy” is sealed and stuffed inside the center stick of the sender , which is made out of plastic (so no metal nor magnet parts ..) and the float slides up and down this the plastic stick …

 

So , how in the name of God can it (“it” may be the green thingy inside the stick) sense the float position/movement trough the plastic ?!

 

Damir

[GLPoomobile 958]

There's a good cutaway diagram in Haynes.

 

Basically, the bit in the glass is a reed contact. There should be a pair of magnets that sit on top of the float, around the outside of the contact. I'm guessing that one magnet will be positive and one negative. When the float falls to minimum, the positive magnet draws the contact together to close the circuit and light the warning lamp. When the float is above min, the negative magnet is closer to the contact and forces it apart...................or something along those lines

 

It looks like yours doesn't have the magnets in it

[DrSarty 90 1 Cars]

'Green thingies' just 'know' when the water/coolant level is low.

 

They're very clever, and they shout down the wires to the bulb to tell you, as no-one can hear what green thingies say.

 

 

 

 

 

P.S. Seriously. My brain aches trying to figure out how the same device on my BMW (robbed) sender works. It similarly has a plastic float with a washer on the bottom face, which as the water level drops touches two pins or prongs. What I don't get (and mine's stopped working too BTW), is why doesn't the coolant act as a conductor and complete the circuit even before the metal of the washer connects the two pins?

 

Perhaps there's a green thingy in mine?

[DamirGTI 325]

I dunno the magnets may be inside the big tube there was something inside but i couldn't make a proper picture of the tube insides

 

Anyway , suppose i buy you an nice ice cream - can you be bothered to make me a scan copy from the joke book ? (i don't have this early Haynes book , i have just the later one which isn't of much use .. )

 

Damir

Edited February 21, 2009 by DamirGTI

[DamirGTI 325]

'Green thingies' just 'know' when the water/coolant level is low.

 

They're very clever, and they shout down the wires to the bulb to tell you, as no-one can hear what green thingies say.

 

 

 

 

 

P.S. Seriously. My brain aches trying to figure out how the same device on my BMW (robbed) sender works. It similarly has a plastic float with a washer on the bottom face, which as the water level drops touches two pins or prongs. What I don't get (and mine's stopped working too BTW), is why doesn't the coolant act as a conductor and complete the circuit even before the metal of the washer connects the two pins?

 

Perhaps there's a green thingy in mine?

 

 

I was under impression that this the coolant one will be of similar sensing system like say the fuel level sender but this the "green thingy" did surprise me a bit

 

Anyone has this sender in working order ? i'm sure that this one on my Ph1 car hasn't been working since i bought the car and neither it does on my other Ph2 car .. at least me thinks so , will try to empty the exp. bottle on my Ph2 car and see if it will react ..

 

One is sure , i really can't figure this out

 

Damir

[EdCherry 34 1 Cars]

I didnt get who these things worked either, id have thought it would be a float system as you say similar to the fuel tank level sender.

 

Also I dont get why none of my coolant bottles have level marks on them! how f***ing stupid. Think im gonna have to switch bottles out to one with a level marker.

[GLPoomobile 958]

Damir, I have both early and late Haynes, and I'm sure this diagram is in both. Look in the coolant system section. I don't have a scanner, but I could try taking a photo and uploading it.

 

The Ph2 sensor is totally different, and the wiring is different. There's been a few topics on swapping the different types of expansion tank and sensor between Ph1/1.2 and Ph2 cars, and so far I don't think anyone has managed to work out how to overcome the wiring and get them to work. Just mentioning this as I interpreted your reply to mean that you were thinking of trying the Ph2 sensor on the car you've removed the above sensor from.

[DamirGTI 325]

You're right cutaway diagram is in the later Haynes as well ! (didn't spot it must admit ..)

 

I'll try to see/test if it works on my Ph2 car ... as i would really like to be known if/when i'm low on coolant .. damn pug electricity

 

Damir

[GLPoomobile 958]

Well I've taken a pic now, so for everyone else's benefit, here it is

 

[DamirGTI 325]

Ah , here's the "green thingy" ! : http://en.wikipedia.org/wiki/Reed_switch

 

.. right , well i'm off to study this

 

Damir

[pug_ham 240 3 Cars]

Interesting, I always thought it was a simple float type switch, when there is enough fluid inside for the centre contact to float there isn't a full circuit so the light is out, when it drops low enough to complete the circuit the light on the dash (should) come one.

 

Clearly one thing on a Pug that isn't as simple as expected.

 

Graham.

[Super Josh 4]

I thought the phase 2 sensor consists of two wire prongs and some circuitry that measure the conductivity of the coolant and switches on the light. Prepared to be proven wrong though

 

 

 

Josh

[DamirGTI 325]

I stripped another sender from my Ph2 car , and they're identical from the outside/inside (as far as i'm aware all LHD cars have white exp. bottle and this type of sender , RHD cars might have both some the white and some the black exp. bottle and looks like this the sender for black exp. bottle is slightly different type and with the 3pin terminal connector)

 

Anyway , this diagram from the Haynes isn't quite correct theres no two magnets inside the sender (one up on the stick and one down on the float ..) at least not in this 2pin type sender , in this sender the magnet is actually that ring inside the float .. and it's just that one .. i tried to slide the float across the "green thingy" and i can notice that it does move the contacts inside a bit .. however when i try to test the sender with the multimeter i can't make it produce any kind of signal

 

If i understand this , the low coolant warning bulb is switched ON when the float with the magnetic ring slides down the center stick on the bottom of the sender tube and thus creates magnetic field around the "green thingy" (which is sealed inside the center stick of the sender) and then , in the presence of the magnetic field , the two contact terminals inside the "thingy" are pulled/bridged close together and by this it completes electrical circuit .

So , the "thingy" + magnetic float in fact serves simply to close the electrical circuit from the low coolant warning bulb to the earth (or to the batt. positive perhaps) .. right ?!

 

Now the thing i don't quite understand is why is slimply impossible to obtain any kind of reading from the sender while testing it with the multimeter by connecting the multimeter probes on the sender terminals and moving/sliding the float up and down the center stick ?!? if it really just closing the circuit then it must be able to activate the multimeter when i set it on the buzzer ? well it doesn't , sliding the float up and down gives zero reading in Ohms and it doesn't react on the buzzer either ..

 

Can it be that the "green thingy" needs magnetic field + electrical current in order to fully make it work/close the circuit ?

 

Damir

[Roman 0]

because reed relay don't work(small glas gizmo -broken or contact is shaged) this is simple on off switch trigered by magnet atached on floating thing inside the sender

[GLPoomobile 958]

Damir, I can't help any further on your query, but am I right in understanding that your PH2 sensor is the same as this float type?

 

On UK Ph2 cars, the sensor goes in the bottom of the tank instaed of the top. It uses two prongs like Josh said. The only one I've seen had severly coroded prongs which snapped off when I removed it, so I was unable to study the ins and outs of how it worked. But I always assumed it worked by the conductivity present in the coolant. Once the coolant is not present, no current is conducted, and the circuit is broken. If this is the case, it answers the question of why the wiring is different between Ph1/1.5 cars and Ph2 cars - on float type sensors it's the completion of the circuit that lights the warning lamp, on the Ph2 sensor it's the breaking of the circuit that lights the warning lamp.

 

Am I right, or am I s*ite?

[GLPoomobile 958]

Why the hell didn't pug make the float like this, instead of a stupid complicated reed switch and magnet set up?

 

 

Inner tube housing a float with a metal contact across the bottom. At either side of the base there is a contact that goes through the body. On the other side of the contact there is a wire that goes up to the cap at the top, and this lot is housed inside the outer tube.

 

When coolant is present float, err, floats! So no circuit. When coolant drops to minimum, float drops down and the contact on base of it completes the circuit across the 2 contacts at either side of the tube. Bobs yer uncle. EDIT: fundamental flaw spotted in the diagram! It would need hole through the inner and outer tube to let the coolant in to make the float float. That could be a little channel directly up the centre through the bottom of both tubes.

 

Pretty much what Graham is thinking, I guess.

 

P.S. check out my mad MS Paint skills

Edited February 23, 2009 by GLPoomobile

[DamirGTI 325]

Yes this other one is from my Ph2 Motronic car , and it's identical float type sender like the one on the start of the thread on the pics from my Ph1 car .. i'm aware about these senders for black exp. bottles but this the black exp. bottles with bottom fitment sender where not fitted on LHD cars

 

I dunno i'll try with new sender (typically , new one cost a bit , around 30.00 quid )

 

Damir

[Tom Fenton 1,525]

Why the hell didn't pug make the float like this, instead of a stupid complicated reed switch and magnet set up?

 

You stupid boy pike!

 

Because the coolant can conduct electricity and so the light would be on all the time regardless of coolant level.

[DrSarty 90 1 Cars]

Because the coolant can conduct electricity and so the light would be on all the time regardless of coolant level.

 

Wasn't that what I asked?

[Rob_the_Sparky 9]

It is a cheap system and pretty universal I think. Bare probes into coolant are going to have all sorts of corrosions issues to deal with - water plus electrics ain't a good idea, hence the sealed system in the form of a reed switch. Fairly reliable as well given the age at which they fail, it is just a shame that they fail in way that is not obvious until you run the engine dry and swear a lot! Been there done that (twice).

[DamirGTI 325]

Been there done that (twice).

 

So, Rob what you reckon , they're fubared right ? i've been just about now trying the other sender on my Ph2 car (the el. loom is spot on in this the Ph2 car .. bulb works as well) and again , no luck , it doesn't switch the bulb either

 

Will buy a new one , these two are obviously broken ... the "green thingy" inside the sender might received some sort of "heart attack" .. in the past when the coolant inside the exp. bottle has boiled/overheated past 100 C or they're failed simply because of the age ..

 

Damir

Edited February 23, 2009 by DamirGTI

[GLPoomobile 958]

You stupid boy pike!

 

Because the coolant can conduct electricity and so the light would be on all the time regardless of coolant level.

 

Yes. About an hour after making that rushed post and diagram, it suddenly popped in to my head. What a tit . And I even commented aout the Ph2 unit working by conductivity through the coolant. Double tit .

[pug_ham 240 3 Cars]

The only way I've managed to "test" the two pin type of sensor (phase 1, 1.5 & UK early phase 2) is with a multimeter looking for continuity.

 

When the switch makes I got an open circuit but getting these to work was as easy as finding hens teeth.

 

The main downside to this type of is if the coolant isn't changed every couple of years the nsides of the sesnor get clogged up with dirt & debris which stops them workling as Rob said. I have managed to get a few working again after soaking them in veryhot (not boiling) water & blocking the tiny holes on the sensor while I shake it to get the level sensor moving inside.

 

Then I've sprayed them with WD40 & done the same again but this doesn't work if they are to far gone.

 

Graham.

[DamirGTI 325]

The only way I've managed to "test" the two pin type of sensor (phase 1, 1.5 & UK early phase 2) is with a multimeter looking for continuity.

 

When the switch makes I got an open circuit but getting these to work was as easy as finding hens teeth.

 

The main downside to this type of is if the coolant isn't changed every couple of years the nsides of the sesnor get clogged up with dirt & debris which stops them workling as Rob said. I have managed to get a few working again after soaking them in veryhot (not boiling) water & blocking the tiny holes on the sensor while I shake it to get the level sensor moving inside.

 

Then I've sprayed them with WD40 & done the same again but this doesn't work if they are to far gone.

 

Graham.

 

Yes that's what i've been doing Graham but i really can't measure/read out anything on the multimeter ..

 

I have one more sender somewhere in my garage (that's the third one !!) i'll see if i can dig him out of the pile of spares and if that one doesn't work either i'll buy new one straight away (or , i might try testing the new one in the store as i have a friendly shop which stocks OE PSA spares)

 

Damir

[DamirGTI 325]

Hooray !! the third spare sender works

 

 

 

 

Damir