Low coolant warning light on

Ruby,my sisters 1985 xj6 has the persistant low coolant warning light on the dash. The coolant level is fine where the coolant is put in. Any help please on what I can do to cause the light to go out? thank you for all of the help in the past. Next area I will deal with is the ac. thanks, Mark

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Access/change the sensor, Mark - it is likely shorted or at the incorrect level? Or simply disconnect…

Frank
xj6 85 Sov Europe (UK/NZ)
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There’s a single wire below and attached to the brown coolant tank.
A black box under the dash measures the resistance: if it is infinite the light turns on, if there is a slight flow of electricity through the coolant to ground the light is turned off. Could be as simple as a disconnected wire.
David

Mark!
I still do not depend on any warning lights, I just change my coolant and
flush it on any engine every 3 years or so.
Walter

Mine failed to light when it should have. I lost an engine… Same with the temp guage.

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Carl,

all the warning lights within the cluster fail to achieve their goal, even if working properly. During daytime you have to shade the lights to be able to recognize whether any of them comes on, irrespective of voltage or rheostat position.

It is a quite common problem that the main idiot lights are beyond the driver’s view, once leaned back and driving comfortably. Even if visible, there is a big chance of missing an idiot light coming on during daytime. A friend lost two (!) Mazda MX5 engines this way. Racers usually connect a relay and a fog light in the footwell to never miss an engine warning light.

Just in case anyone has an idea about how to increase brightness of the clustered warning lights, I’d be happy to learn about !

Good luck

Jochen

75 XJ6L auto (UK spec)

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You can swap in a S3 cluster that should light up a lot better? I have one if you want to try, it has two lamps more than the S2 I think but that should be fine. Increase the wattage is the other option.

My warning light doesn’t work and I found out when the temperature began to rise and sink rapidly. No damage… a few (5+) liters were gone.

Aaaahh … really? I wasn’t aware of that. What did Jaguar do? - Beef up the bulb or make the “windows” more transparent. While the “lighted text” was a miracle to look at ages before LED screens and while other cars were well-equipped with two idiot lights, it works only in the dark.

In any event, I’ll keep that on my list. Once you’re back to Konstanz we might arrange for a test.

Thanks and all my best wishes

Jochen

75 XJ6L 4.2 auto (UK spec)

I‘ll go through my collection. I think the symbols grew larger and more legible, mostly, works for me! We can compare then.

It might worth a try to fit one or two bright LEDs in there?
I did this on the High Beams light on my S3 and it did made a difference.
Otherwise, as David said the S3 cluster works ok. (I have one in good shape if you are interested).

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Thanks Aristides!

Indeed, I’d really like to keep that 70s charme of lighted writing against black, even though Jaguar may have realized there was a problem as you should get aware of warning lights also during daytime. But thanks for your kind offer anyhow!

LED bulbs sound interesting - did you find any for the exclusive size used in the warning lamp cluster?

The longer I think of it the more I get tempted by the idea of looping in a really bright red light for the oil pressure warning light.

Best

Jochen

75 XJ6L 4.2 auto (UK spec)

You can always fit leds or chop one up!

No, a generic LED with a 600 Ohm resistance in series.

Would that work with the alternator as well?

If it has a resistance in parallel (mine does) I think it would, but I haven’t tried it.
If it doesn’t have the resistance I’m afraid that the LED will not let enough current through to excite the Alt. Of course you could add a resistance, also a safety measure in case the bulb/LED burns.

So you need 600 Ohm in series + resistance (how much) in parallel to make up for a simple substitute?

To excite the rotor you need current passing the control lamp + a certain resistance in order not to fry the rotor. What resistance would be your target?

Best

Jochen

75 XJ6L 4.2 auto (UK spec)

Correct.
The parallel resistance is there to excite the amp in case the light blows out.
I don’t know it’s value, but I could check latter in my spare parts.
A light bulb is usually around 3 to 5 Ohms, so I guestimate a 5 Ohm / 5 W resistance would work.

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Most alternators will self-excite, Aristides - due to remanent magnetism…

That said; resistances in series is added for total resistance. In parallel circuits, you inverse the resistances for each parallel and add up the fractions to get conductivity. And the inverse of conductivity is the resistance…:slight_smile:

Since the LED resistance is very high in this case - the bypass resistance is about equal to the original resistance of the 1,2W cluster lamps; around 10 ohms. But I suspect that even a tiny current is enough to excite the alternator…?

Frank
xj6 85 Sov Europe (UK/NZ)
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