1983 xj6 low water sensor

(Testie2) #1

Can anyone tell me how this works? I can see that the wire from the dash warning light goes to the pin which inturn pokes into the overflow reservoir. Does that then suppose to earth through the water in the tank to turn the warning lamp off? If I earth the pin to chassis the light goes out but even dangling it in water does not!
The tank seems to be sealed and there is no parts rattling around in it.
Just reading previous post ‘

(Testie2) #2

Just figured it out! someone on another tread mentioned that the sensor would not work with distilled water but i have been using tank water(rainwater). The water up here must be pretty pure as when I added more antifreeze the light finally went out.
Hope this might help someone else

(Frank Andersen) #3

Interesting, Col…

But since essential ingredient in antifreeze is corrosion protection the recommended mix is between 35 and 50%. What mix did you use before and after…?

xj6 85 Sov Europe (UK/NZ)

(Testie2) #4

Frank, it all started when in extreme hot weather and a very long pull up a mountain, about half an hour climb, the better half had to stop at the lookout. She boiled and would not cool down and the cap on the expansion bottle was remove and quite a lot of fluid escaped. With the motor running it was filled with rainwater and an hour later we stopped again and added more. Since then I have only add rain water until I removed the tank, checked that there was nothing fallen off inside, flushed it out and refilled with tap water. Multi-meter set to ohms proved that straight tap water is not conductive at 12V or what ever is left of the circuit seeking earth potential. Adding antifreeze anti boil to the water fixed the problem. Now I can drive without the nagging worry that i might be low on coolant I will drain it and refill with 50% mixture. Thanks for your interest.

(David Jauch) #5

You opened the cap of a boiling car? Brave. Apart from that when overheating it helps to go into full heating, shift down a gear maybe, and open the hood. Very interesting about the coolant sensor. There is a control box that must earth the lamp when there is no current through the water, and as soon as there is a little it turns the light off. Good to know, thank you. Also I always try to carry some water, and somehow it’s always somebody else I eventually give it away to.

(Carl Hutchins, Jr. ) #6

Wow !!! My lessons for the day.

  1. I lost my DOHC to the failure of the unit to warn me. That and the misleading temp guage on the facia.

  2. The warning sensor relies on water as an electrolyte ?

  3. I’ve always had spare water aboard.

  4. Early on, I was taught to not open the radiator cap on a hot engine., No benefit only harms. Loss of coolant and danger of burns…


(Testie2) #7

Wait for quite a long time and wrapped a towel over it. Was hoping it was cool enough as it had stopped relieving itself out of the overflow. Live and learn!

(Frank Andersen) #8

Coolant mix boils at some 102C, Col - pressurized to 15 psi raises this to 120C…

As the engine’s inside is much higher than 100C when stopped; explaining the boiling at the look-out. Removing the cap depressurized the system - and the coolant turned to steam. Which expanded and forced out a lot of coolant, as expected. And David is right; removing the cap on a boiling engine is…hm…a bit reckless…:slight_smile:

It’s the pressure, not the antifreeze, that raises the boiling point - and the pressure is limited, by intent, to 15 psi by the expansion tank filler lid. So, past 120C it will sure boil…:slight_smile:

I have always thought that the light came on when the sensor was grounded - but your clarification made me look closer. And sure enough; a low coolant control unit is involved - thank you! :slight_smile:

xj6 85 Sov Europe (UK/NZ)

(Testie2) #9

Just thought it might be cool enough to add what had been lost out the expansion tank through the overflow. It was so hot weather wise I did not think it would ever cool down! They say you learn from you’re mistakes so there is another lesson learned.

(David Jauch) #10

I am guilty of removing the cap off of warm cars, too, but there are horror stories: the water suddenly gushing out after a short delay is one. And if you wannt to see something interesting, turn the engine off and after a minute turn the ignition on and find the temperature is much higher than usual.
The ideal solution to overheating is to drive away swiftly with maximum airflow (heater core, hood open,… but the second best might be to let it idle a bit. If it overheats for no reason then it is shut down, quick for me. My BMW once ran into red suddenly and sure enough, there was not even enough water in the radiator to reach the sensor at half height. The expansion tank was bone dry and I still wonder how the head gasket, now 30000mls overdue, still holds up. Another reason to switch into full heat because then you know if there’s at least some water still in there!
I offer 106° at 50/50 mix but how can it act as anti-corrosive when it conducts significantly more than water? I thought that was one of the goals!

(Carl Hutchins, Jr. ) #11

Yeah, shut down, No coolant flow, no air flow. heat goes up!!! Despite no combustion.


(Frank Andersen) #12

Yes, Carl - and if the engine is really, really hot, coolant lost; the temp may rise high enough to seize the pistons…:frowning:

In such a situation; the engine must be rotated by fair means or foul - it’s a tough call…

xj6 85 Sov Europe (UK/NZ)