When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I've suddenly started getting the dreaded "Coolant low" light and message on the dash (interrmittently), although the level is fine when I check, and I had the thermostat, housing, hoses etc. all replaced early this year. It's my understanding that the sensor responsible for this warning is in the bottom of the coolant recovery tank, but I'm not sure how it works; is it a float device, or some sort of a resistance sensor? Can it be serviced\cleaned\repaired, or is it a throw-away, and can it be purchased on its own, or is it part of a new tank assy.? Thanks in advance.
there are 2 components --a floating ring presumably with a magnet in it and a detector/sensor inside a tube around which the ring floats. Usually the detector fails and or wiring. I do not see a a separate part no. You can change the sensor without removing coolant.
Renovator, I've topped mine up to the point where it simply pushes the excess out the first time I get the system up to temperature. Braking sharply, or descending a steep incline seems to be enough to set it off as it approaches normal operating temp.
Six Rotors, do you mean that I can change out a sensor with the tank in situ, or simply that I don't have to drain the entire system to get the tank out to work on it?
In situ. You must a bunch of cars there with sensors!!!!! (PS I had you confused with Robert Laughton, who has lots of spare cars hanging around, when I made this smart *** comment)
Last edited by Six Rotors; 11-23-2020 at 07:37 PM.
The only thing that activates the 'Coolant Low' fault is the float inside the coolant reservoir. If the float contains a magnet, I would highly suspect that the magnet has become dislodged. In this particular case, it might be better all the way around to replace the coolant reservoir, but better be prepared to replace the small diameter rubber hose on top as well since the plastic nipple on the coolant reservoir will likely break off while lodging inside the rubber hose. Yes, the float is located inside the coolant reservoir. In the meantime, I'll see if I can provide a part number for the small hose and the coolant reservoir when I'm back in town tomorrow morning. The part numbers which I will provide for those two items would be for a 2005 Jaguar XJ8L.
Just for clarification I have attached 3 pictures showing the new spare tank I have on my shelf----I bought it several years ago and of course both my 4.2L engines have not had problems with tanks since. It is obvious there is a removable sensor which can be removed without draining the tank. You can hear the magnetic ring when you shake the tank. You cannot access the ring without destroying the tank. Coolant Level Sensor and tube it fits in. The float fits around the tube. Sensor located on bottom of tank Part number of new tank
Last edited by Six Rotors; 11-23-2020 at 07:07 PM.
I'm going to pull the tank this week (We've already celebrated Turkey Day up here) and see what's up. Will keep y'all posted.
Hi Robert,
You don't have to remove the reservoir to access the coolant level sensor. Just remove the one 8mm screw that secures it to the upper radiator support, then slide it a little to the right (right while facing the engine compartment - technically toward the left side of the vehicle). Sliding the reservoir will pull two tabs out of rubber grommets on the mounting bracket and give you enough range of motion to raise and tilt the reservoir forward slightly so you can see the coolant level sensor. Just be very careful not to strain the small hose plastic nipple(s) that Rickk mentioned.
Inspect the wiring at the electrical connector - it is very fine and fragile. You can disconnect and clean the connector. To remove the sensor, twist it slightly and slide it out.
The sensor is a reed switch. It fits inside a hollow tube molded into the bottom of the reservoir. Inside the reservoir, a floating magnetic ring rides up and down on the hollow tube. When the coolant level is correct, the magnet floats above the reed switch. The schematic shows that the switch is normally open. If I recall correctly, when the coolant level is full, the magnetic float rises above the switch and leaves the contacts open. When the coolant level falls, the magnetic float lowers over the reed switch and the magnetic field closes the switch contacts, completing the circuit to ground and illuminating the Low Coolant lamp in the instrument cluster. I may have that backward.
Other possible causes of the Low Coolant lamp include a stuck float ring (you may be able to free it with judicious taps on the reservoir), a shorted sensor, shorted contacts in the electrical connector, or a short to ground in the electrical harness. Also, the float may loose its buoyancy, or may be more buoyant in 50/50 coolant than in pure water, so it would be worth confirming that your coolant mix hasn't become too weak (biased toward distilled water instead of a 50/50 water/antifreeze mix).
Hi All;
Well, I finally got around to pulling the tank, with guidance from Don B, and while I understand the system a little better, I am no closer to resolving the problem. With plenty of coolant in the tank, a cold start-up shows no problem. As the engine temperature begins to rise, however, with the dash temperature gauge indicating roughly two thirds of the space between "cold" and "normal operating temp" , I get the red light and 'COLANT LEVEL LOW" message. Checking the tank shows that the level is as high as possible. As the dash gauge reaches the half-way,'normal operating temp.' position, the message and light go out. The tank is clean, and shows no sign of sludge. The probe is spotless, and the connections are clean, although I gave them a shot of contact cleaner just to be sure. The float donut in the tank moves freely, and opens and closes the circuit as it moves thru its range. (For what it's worth, Don, in my setup, a low float level produces an open circuit; a top float position closes the circuit.) I suppose this would make it harder to defeat the warning indications by just unplugging the probe. Some have indicated that they were able to clean mild scaling off the probe, but since my probe remains dry in its tube, and never touches the coolant, that doesn't apply to me. I guess the next step is to order a new probe, and repeat the drill. I'll report then.
And now I am told by Jaguar Thornhill that the probe is not available separately from the tank assembly @ $178.91 CDN. Plus HST and shipping, of course! Santa; are you listening??
The probe is spotless, and the connections are clean, although I gave them a shot of contact cleaner just to be sure. The float donut in the tank moves freely, and opens and closes the circuit as it moves thru its range.
Based on your report above, I wonder if a new sensor/probe will solve your problem, since moving the magnetic ring over it seems to open and close the contacts properly?
The repeatability of the warning message at the same spot on the temperature gauge has to be a clue. I just can't think what it means. As far as the schematics show, there is no direct connection between the temperature gauge and the low coolant warning lamp. The coolant level sensor connects directly to the Instrument Cluster. But the Engine Coolant Temperature Sensor communicates directly with the ECM, and the ECM passes the reading along to the IC via the CAN.
One idea to rule out the sensor would be to disconnect the sensor and jump its harness connector with a paperclip bent into a U, temporarily secured with a little tape to hold it in and maybe tied up to a hose to keep it from getting caught in the belt. If the low coolant warning still comes on, it's not the sensor.
Could it have something to do with when the thermostat opens, causing either a momentary fall in coolant level in the reservoir (perhaps due to air trapped in the system?), or turbulence in the reservoir due to the stream of coolant returning from the radiator?
Could corrosion on one of the connectors between the sensor and either the IC or ground create a temperature-dependent problem? As I recall the sensor signal passes through a large connector near the right edge of the radiator, and another connector at the base of the right-hand A-pillar. The sensor is grounded "below the Front Power Distribution Fuse Box," which I think is really one of the two ground points behind the right headlamp. I had to track those coolant level sensor connectors down earlier this fall on an '06 that had significant front-end damage and the sensor wire had been torn apart somewhere between that connector at the radiator and a point near the right wheel well.
I'll keep trying to think of ideas. Let us know if you make progress.
And now I am told by Jaguar Thornhill that the probe is not available separately from the tank assembly @ $178.91 CDN. Plus HST and shipping, of course! Santa; are you listening??
Reading your last post, the proverbial light-bulb went on (it's dimmer these days, but it still works!) . I changed out the right side HID bulb a few weeks back, and I had to loosen the grounding point behind the headlamp assy. to get the new bulb into place. I took the thing apart again, cleaned up all the surfaces and sprayed them with anti-corrosion compound, and re-tightened the nut as much as I dared. I have run the car thru three warm-up cycles now, and no warning lights! Ta Da ! Got my fingers crossed, but Thanks again.
11-23-2020, 08:03 AM
"Coolant low" light on
