G'Day fellas,
I get this messege intermittently despite no engine temp problems as well as checking overflow reservoir (no probs with liquid level). The wiring harness connector underneath can be disconnected and that will reproduce the error message. The fitting underneath the reservoir, however, seems like it should be solid but it rotates L to R about 1/4 inch.

Inconsistantly with bumps or vehicle attitude change I will see this warning on the message center come and go. This message keeps blocking useful trip data and will also create the 'boy who cried wolf' syndrome and I will probably miss other warnings as I get used to ignoring the message center.

Anyone here with some advice? Do I need a new sensor or is there another angle I should be checking?

Thanks in advance,

John W.

I must be missing something.....
What year and model?

Generically speaking, sensors can be a 2-wire probe or most common a float and contacts (not necessarily for Jaguars).
Cars with floats can have floats sink, stick, contacts bad, corroded, cracked housings, or just worn out.

If it was my car, I would drain the reservoir, remove the sensor, clean, check float and operation, re-install and refill, test.

If probe style, clean not only the probes but especially the insulation area between probes and connectors.

Thanks TOC - I'll take your excellent suggestions and give it a shot.
By the way, it's a 1998 XJ8 VDP with the AJ8 motor.

Thanks again,
John W

Ah.
THAT model.
A whole lot of folks have issues with that sensor, it seems (do a Google search).
Try cleaning, be prepared to replace it.

Okay, I checked.....with a friend who runs a Jaguar dealership shop.

Float.
BIG problem, same as on the Land Rover.
Not replaceable separately.

The switch is, but not the float.
You get to buy the whole reservoir.

OR.....I would dry the float out very well, and see about sealing it.

The test is to unplug the sensor plug, and fabricate a wire with tabs to jumper the plug in the harness (and tape it up to keep it from shorting against something....errr.....metallic in nature.

Then drive it for a week (and visually inspect the reservoir level).
If the light never comes on, that's it.
If it does, it's in the electronics somewhere.

Help?

TOC - you are awesome. I haven't had a second to get anything looked at yet (except staring at the bloody warning message too often on my 3 hour roundway commute each day!) I am hoping to have a go at it on Monday. I've seen brass carb floats leak in old snowblower and lawn mower fuel bowls but it bugs me that Jag would have this leak issue with a coolant sensor float! Either way I am going into this with some great advice and I want to thank you in advance. When I do this I'll try to make a collage of my efforts and maybe some other folks will benefit - especially if I can get it fixed without screwing it up or shelling out $$$ for a whole new reservoir assy. Cheers mate!

John W

Hi TOC,
I emptied and removed my coolant overflow reservoir to inspect and get familiar with the float and sensor operation. The sensor looks like the image I attached (if it shows!) and the float seemed to work fine (not stuck or sinking). The coolant that I removed looked bloody awful (like a mix of green and pink types) and I am wondering if that could be part of my problem. I haven't tested the electrical yet, I am just getting myself aquainted with the components. For the time being, I have re-installed everything after making a more secure mounting connection for the sensor (to stop it rotating / wobbling) and topped the reservoir up with some clean water. I'll keep you posted once I try the electrical test (jumper across the harness connector).

John W

This is the color of the coolant that I drained out. What color should dexron III be? This stuff looks like swamp water.

That's the clour of Dexron....except you want green anti-freeze, not red transmission fluid.

Japanese antifreeze is red, and maybe new Jags call for red, don't know.

Does the float.....float?

Clean the parts, flush it all out, use a toothbrush on the moving bits, re-assemble and try it out!

Hi Toc,
Yes the float floats and I cleaned it all up before reinstalling. The float is a 1" diameter cylinder that runs up and down a 1/4" sealed tube. It has plenty of room to move. The sensor goes up into the sealed tube from underneath the reservoir and I imagine it senses the position of the float inside the reservoir via magnetic induction or something similar. I am hoping that the teardown, clean out and reassembly is enough to get it figured out - I have used that trick on many different things over the years and it has worked many times despite the lack of any obvious findings!
The coolant color concerned me because I cleaned up some spilled coolant with white paper towel and it came up pink on the paper.

I will run it for a week and report back with the results. Fingers crossed!

1 week later and 600+ miles on bumpy Wisconsin 'Class B' roads and all is happy in coolant sensor-land. Whatever I did, it worked. Thanks for your advice and research TOC, it has helped my sanity immensely!
John W