I have recently been getting a low coolant level warning, even though the coolant level is where it should be.

Today I drained and removed the coolant reservoir and checked out the low level switch, which worked perfectly with a magnet, and also in situ by turning the reservoir upside down with a DVM connected to the two switch contacts. This proved that the switch was functional, and was also operating correctly with the internal float. I have had problems with other systems whereby the float has failed and filled with liquid, but it doesn't seem to be the case here.

I only seem to get the low level warning after the engine is at normal running temperature, so my question is does the 'Low Coolant Level' alarm get enabled ONLY by the low level switch, or does the ECU also monitor coolant temperature and decides that there is low coolant if the coolant temperature is high? My temperature gauge is modified (jagwrangler) and shows the correct temp., and has never gone much above the 200* F. mark.

My next step is to run the engine up to temp., and check with an IR thermometer, but I thought I would throw this out there first.

Any thoughts appreciated!

Thanks,

 

Remember that this is an aluminum block and most everything will expand and contract with the change in temperature. The system is designed to use the reservoir as a holding tank and the system expands and contracts to compensate on the fluid level, when this does not work is is often caused by a bad tank cap of a leaking reservoir.

Link JagRepair.com - Jaguar Repair Information Resource

 

So far as I know the low coolant level message is only triggered by the float switch.

 

I did some further checks yesterday;

+Coolant level full.
+Ran engine at idle to 185*F, everything cool (Literally & physically)
+Increased RPM to 2,000.
+Reached 200*F, still good
+Temperature gauge goes a touch over the 200* mark, and I get the
Low Coolant Level alarm.
+Decrease RPMs and engine returns to 185*, still have the low level alarm.
+Switch off engine and let cool for an hour. Rechecked coolant level and still full.
+Start engine and no alarm.
+Repeat all the above, and alarm returns again at just over 200*

The radiator fans did not operate at these temperatures, although they did come on as expected when the AC was actuated.

I can only think that there is a temperature related problem with the level switch. A bad contact expanding/contracting? Something screwy with the magnetic float? I am a bit reluctant to cough up $200 or more for a new reservoir & switch until I can figure out what is happening here. I have a couple more things to try out today.

 

My bet would be a leaking float. The float can leak and become sort of neutrally buoyant. From a cold start, the coolant outside the float gets hot first, and so a little less dense. Then the slightly cooler, denser coolant inside the float causes it to sink.

With things cooled down, you should be able to stick your middle finger in there, find the float, and feel how it's acting ... it should feel like it really wants to float.

There are some old threads dealing with this: some of us played with putting a little floatation aid under the float for this situation, but I can't remember if anyone was able to achieve a fix this way.

Good luck.

 

Thanks Dennis.

I am also thinking about the float. In my years as an electronic's tech I have had several instances where a leaking float has caused problems, but not where the temperature made a difference, although there is always the first time. Shame I can't get 'fingers on' to check for sure, but that's life with a Jag for you!

 

Another option, if I remember this right, is to shine a light down into the expansion tank, push the float down a bit with a tool of some sort, and watch it react. It should come back up quickly.

 

The float is solid and in my experience and testing the float did not fail.

 

Here's one thread describing a float-related failure, in this case the float magnet falling out ...
https://www.jaguarforums.com/forum/x...coolant-72215/

Hard to see how this could cause your specific symptom though.


Somewhere, there are thread(s) about the float losing buoyancy, but it's too nice a day to look for them now.

Good luck!

 

I just remembered where it was. Spurlee's post #135 from this thread ...

https://www.jaguarforums.com/forum/x...d-80074/page7/

... was as follows ...


Finally resolved...
It's been a few days running now without the Low Coolant light. I'm pretty comfortable in saying it was the weak/saturated float all along. When I finally got the booster float to work properly the problem went away immediately and has not returned.

A new expansion tank will get you a new float - that's the $170+ solution. Fixing up some sort of booster to help your ailing float is free. I used a 1" plastic ring (tested to make sure it floats!) cut into a "C" shape and snapped onto the post, under the float. It took less than 15 minutes.

Thanks to all who helped along the way, it was an interesting experiment!
__________________
Scott

 

I used a foam ring from a DVD spindle under the float. Still working. Search for "low coolant message -resolved".

 

The float is solid and I did all I could to make it sink without adding weight and could not so my guess is the float is ok.

 

I was the guy with the "life vest" solution and, yes, it has worked for several years now. You are correct, the action of a saturated float changes dependent on the temperature of the coolant. That's what made it such an interesting problem to solve. Without a doubt, a saturated float is the OP's problem.

The fix took 5 minutes once we understood the problem. I took a ring of plastic (about the size of a really large candy Lifesaver) that floats and cut it into a "C" shape so that it would snap on the post under the saturated float. It provided just enough lift to keep the reading accurate.

 

Yep! And it is still working!