This is another message problem I have. This message comes up often. The engine coolant is not low so that is not the problem. I also go and take the cap off and then reinstall it making sure it is tight. It goes away for a short while then back on again. Here's my thinking on this. There are three form fitted hoses that come into the reservoir. There is a plastic cover over the reservoir. The cover slips and slides. Is there a possibility the cover hits one or a couple of those formed hoses and that creates the signal for the message (affects the sensor on the reservoir)? The cover appears to show no other purpose then esthetic.
Thanks,
Bill

 

The coolant level sensor can dirty/sticky. You can remove and try to clean any debris/gunk from inside it and/or get a new one - about $50 to $60 - google 'XJ8 coolant sensor'.

 

My coolant tank just about drove me crazy. The coolant level low then normal! If you are not adding to the coolant then go to my page http://www.gusglikas.com/AutoRepairCoolantTank.htm not sure the tank is the same (you do not have the year posted) but I would bet the probe is. I would recommend checking the probe first and you can get them @ http://www.motorcarsltd.com/

I need to correct my page. I see that I called the level probe a temperature probe and that is incorrect.

 

THanks for the link Gus. From your page it appears that the sensor works as following:

The float has a magnet embedded in it. The probe has a magnetic reed switch in it (the glass tube). The float is coaxial with and surrounds the probe.

When the coolant level is high enough, the float is also and the magnet is far away from the switch - switch is OFF. When coolant level drops, so does the float, the magnet moves close to the switch, causing it to close (ON). (i'm using open and closed here, but it could just as easily be closed/open, I don't know the relative position of the float to the probe as a function of coolant level, can't tell from your pics - But, the important thing is that motion of the float causes the switch to change states)

Don't understand why cleaning the probe affected the measurements, but as long as the resistance changes were minor, they should have no effect on the sensor on/off function.

I would expect that dried gunk that's built up and dried on the surfaces of the float and/or the surfaces upon which the float slides will inhibit its motion, preventing it from moving with fluid level. So, once the fluid level has dropped, and the gunk dries in place, the float may get stuck in the down position.

Seems like a good cleaning should get all back in order. If I'm stating the obvious here, I apologize. It looked from your page that you had not yet determined function of the sensor.

 

Quad,
I found it a little hard to understand why it was not working properly myself. The sensor is inside a channel that the float/magnet goes up and down depending on the fluid level. When I tested it I got open and close indications as the fluid level was going down. Now I was watching the float as I was testing and it was not going up and down sporadically, it was consistent with the water level. I took the probe out and cleaned it and also was scraping the outside of the probe to see how it worked. I reinstalled it and it worked fine.?!. The only thing I could figure out is that the probe had a calcium buildup around the probe and the channel it was in. Cleaning it allowed it to read the magnet properly. With the one in my car was completely deteriorated. I do not claim to have the answers on this I can only tell you what I came up with in my test.

 

Since it is a simple magnetic switch - and when working properly your pics show that, all I can guess is that the debris was intefering with the magnetic field (ferrous material in the debris?) or the scale on the probe was keeping the magnet from getting close enough to fully engage the switch. All conjecture, but it is such a simple sensor that not too much can happen.

 

Well that is the way I see it. Hard to explain but it works for me.

 

Bill I have exactly the same situation with my low coolant warning light coming on and the coolant level is fine .I have been told to check and perhaps clean the coolant level sensor in the bottom of the expansion tank and check also the float is not stuck but your suggestion is easy as I can remove the cover and it is only there for aesthetic reasons and try for a week or so. will report back

 

Hi Experts .Have been loosing a little coolant for a while enough to bring low coolant light on but plenty still in expansion tank and no overheating problems at all and have checked everywhere but cant find any leaks from hoses or radiator and have replaced coolant outlet and had aluminum thermostat and of course new chains and water pump .The car runs perfectly although we have noticed very slight miss on start when cold but slight blip of accelerator and idles and runs beautifully and would think it is perfect. A few drops come out the overflow when fill it up expansion tank with coolant but not enough for this to be the source of leak .The car has only done 10300kms/63000miles .My mechanic today is suggesting that there maybe a leak in the cylinder heads which scares me a little.It is winter here in Adelaide and when started cold after being outside over night there was white smoke coming out of the two exhausts but thought condensation .Also my mechanic says there was a little blue smoke but the car does not seem to use any oil at all none since last serviced 3000kms/16000 miles ago . The oil is perfectly clean and no sign of water or anything else in the oil and under oil filler cap absolutely clean .
Would love some advice could it even be the inlet manifold which I have had on another car but maybe just hopeful on this .
Regards
Nigel Adelaide