1984 XJ6:

Wednesday morning, the coolant warning light stayed on after startup, so I shut down the engine before it could get hot and put a few ounces of coolant in the reservoir to the level it's previously been happy. Upon restart, the light stayed off and remained off the rest of the day. I didn't use the car after Wednesday evening until...

Saturday morning, the same situation. I thought I must be losing coolant but this time, the level seemed unchanged from where it was Wednesday but I added another ounce or so and, again, the light stayed out. Used the car for a few hours and not again until

This morning (Monday), the low coolant warning light stayed on after startup. I shut the engine off, checked the coolant level and it's still looking nicely full. Mindful not to overfill the reservoir, I put about another ounce of coolant in and the light stayed off after restart.

I'm not seeing any coolant on the ground (not that I would, necessarily) and, while I am using the heater pretty consistently this last week, my carpets/floors are dry.

I realize I could be losing a small amount of coolant and a pressure check might answer that question, but given that the reservoir doesn't look like it's losing fluid, could it be electrical? Is there some way I can test the sensor? Or something common to these cars I should know about?

Thoughts?

Thanks in advance,
Rhett

 

Your car has the brown plastic header tank, correct? (I think it was 1982-83 that the change was made)

As long as coolant is covering the sensor (which is fairly low in the tank) the light should stay off.

Syphon out the tank and remove the sensor, clean it, reinstall. See what happens. Might wanna order a new seal for the sensor ahead of time

Cheers
DD

 

Thank you Doug. I'll try that.

 

Sorry for the thread revival but this same symptom has been cropping up my vehicle as well.

Topped it off but the light never went off after the first time and given that its the middle of a hot summer and my temp. is as cool as ever and my coolant has remained at the fill level for weeks now, I'm virtually certain this is a sensor or wiring fault.

was wondering, Rhett has your sensor cleaning went toward resolving the low-level light being on? any others with thoughts or input here?

 

There's also a 'low coolant transmitter' behind the dash...weird gizmo....but they almost never fail.

Dirty or faulty level sensor in the tank is the most common problem

By all means inspect the wires to whatever extent possible


Cheers
DD

 

It's not very helpful but I sloshed a long cotton swab (the kind with the long stick) in and around the sensor and the problem went away. Probably not a long term fix but seemed to point to the sensor needing a better contact with the fluid.

 

Low level coolant light!!!! Brings back bad memories!!
When my 4.2 met it's demise, apparently by a major loss of coolant,
the light remained dark!!!


I've not investigated it's workings. But, it seems to be more complex than mere float. In the right scuttle is a cylinder likened to an old tech camera film canister. It has a bunch of wires, one of which is a white one. That designates "ignition switch on" power.


My brown plastic tan has departed to serve another, sensor and all.


My present system is open the radiator cap and look for coolant....
Only when the engine is cold, of course....


Carl

 

Again, sorry for reviving my own resurrection of an old thread but I found this wire excessively loose and basically just dangling freely from the area just to the front of the expansion tank - glad it didn't get caught up in the compressor.

Where do I connect this white/red wire? I imagine this is related to the low coolant light being on falsely.

 

I'm sure you've figured it out by now but for future readers: that's the problem. The red/ white wire connects to the coolant level sensor at the lower front of the expansion tank. The light will stay on if not connected. Be sure to clean both ends of the connector - I've had a problem with the light staying on simply because the slide-on disconnect connector was corroded and therefore not making contact.

 

As years have morphed into decades degraded connections are more common. Whenever you work on the car take a few extra minutes to clean the connections in whatever area you are working....even if no problem is occurring. In so doing you'll be preventing problems down the road. The majority of the much-ballyhooed "Lucas" problems are solved by cleaning connections and grounds.

Cheers
DD

 

The sensor is failing...

 

Whilst the parts book might refer to the probe in the water tank as a sensor, it is merely a ground rod. There is nothing that can fail with this component other than a poor connection at the lucar connector, or possibly a build-up of silt on the surface.