I've been playing with my coolant system for a few weeks, and reading the various threads here on the topic have been helpful in getting me this far. I'll provide a little back-story before I throw out a few questions in hope of getting a lead on my next step(s).

Backstory:
After having my Jag for about a year, I had the low coolant light start coming on intermittently as I went up or down hills or braked sharply. Adding some H2O bought me about 6 more months before the issue returned. Looking around a little, I could see obvious signs of a weak seal at the upper hose coming off the reservoir towards the passenger side. When I had my XKR in for a brake flush, I asked them to take a look at the hose figuring they would replace it. The story I got back was that the housing was cracked and the thermostat should also be replaced. When I pushed them for their reasoning on the thermostat replacement, it seemed they were just looking for a couple hundred extra bucks in labor for some likely unnecessary work (last time I go to Brakes Plus!). Last weekend I drained the reservoir with a turkey baster and tightened up the clamps on the hose - a small screwdriver pushing the clamp closed through the punched notch and then a pull up unlocks the clamps fairly easily, after that a little extra crimp before closing them back up adds the extra tightening.

Running the car the next day, there was no longer a leak; however, the low coolant warning was on constantly. A little research made me wonder about the magnetic rod on the float. I redrained the tank, and sure enough, the rod was lying at the bottom of the tank. My assumption is that I accidentally knocked it loose with the baster - for reference, baste the corner of the reservoir towards the passenger, the corner facing the driver has the float in it. With the limited space available through the cap opening to work with, I used a skewer to open up the hole on the top of the doughnut float that I assume the rod lived it, and then used a circular file to shove the magnet back in with some force. I filled the tank back up and the coolant light remained off until the first time the supercharged kicked-in. The light then remained on. I assumed the magnet rod had knocked loose again and today I drained and removed the reservoir in hopes of permanently repairing the float / rod.

Upon draining the reservoir, I now know that the float is not removable - it must be installed before the reservoir is welded shut. I also found that the float had come fairly far up the guide post, and the magnetic rod was still in-place, but wedged against the outside of the portion of the reservoir that serves as the stop for the rising float. Knocking the float back from the lodged position left it at the bottom of the guide post but turned off the low coolant warning - unfortunately this is the position the float assumes when the tank is empty, so only an empty tank was turning off my warning. I then determined that the stop at the top of the guide post that stops the float at the end of its travel is actually a inverted cup, and there is room for the magnet rod to go inside the cup (as opposed to outside the cup where mine had previously gotten lodged). Pushing the rod towards the middle of the guide post now allowed the float full travel with the rod going into the recess at the top of the cup. However, with everything remounted and reinstalled in this position, I now get a low coolant light when the float is all the way up and the rod is recessed into the cup. When the float is at the low position, the warning goes off.

So... my questions as I attempt to determine if I've got the rod in the right place:
- Is the rod supposed to be sticking out the top of the float?
- How far is it supposed to protrude from the top of the float? (I'm thinking mine isn't in far enough, and this makes it to too high to detect in the full position, and puts it in the full position when the float is low.)
- Is the magnet suppose to recess into the stop when the float is at the full up position?
- I'm close to just buying a new reservoir and moving on with my life... Any suggestions on other courses of action?

Thanks in advance.

 

Like you I will always make an effort to fix things but you have given it a fair effort and there is nothing worse than a come and go failure. I have owned two Jaguars and 5 coolant reservoirs.

 

There's a huge thread on this problem here
https://www.jaguarforums.com/forum/x...esolved-80074/
I think you're going past the sweet spot for the reed switch.
If you put a meter on the sensor you can adjust it more easily.
Obviously use the continuity range to see the reed close.

 

This is what my float/magnet looks like.

 

My erratic, and mistaken, low coolant warning was solved by replacing the coolant reservoir and the sensor.

The sensor alone did not do it, and the reservoir kits came with a sensor so that turned out to be a wasted $75. The clips for the hoses were still stock but had to be replaced after they began to leak.

 

A picture is worth a thousand words. 80% of my magnet is sticking out the top of my float. If I can figure out a way to fully seat it into the float as yours is, I believe my problem will be resolved.

 

I should have said that my low level warning indicator does seem to be completely random when completely topped up. This along the tank perferation lead me to order a new tank from Jag. Just arrived today.