I wondered if someone could explain how the sensor works? Before I removed the radiator, I kept getting the "low coolant warning" alert even when the tank was full.
Thanks,
Bob

 

I believe that when it is immersed in coolant it keeps a ground circuit open....no light...if the coolant drops and it is dry, so to speak, it closes and completes the ground....light on....loose or corroded plug in or faulty sensor could cause a continually light.,.you could use an ohm meter to verify operation

 

You did not indicate your model year or engine type. I believe that on the 2003+ V6 equipped cars, the sensor is not replaceable and a new expansion tank is required to cure this fault.

 

Thanks and you are right the sensor is only available as part of the coolant tank. Rock Auto Parts has a good price on them.
The car is a 2003 Stype 4.2L with 117,000 miles. I'm replacing the radiator and just was curious about the technology used in that sensor.
Bob

 

when you have the radiator out, inspect the trans cooler lines really good.... especially the rubber to metal crimps....the sway bar bushings are a breeze to replace at the same time....if you decide to replace the rubber portion of the lines, there are some detailed posts on that job here on the forum...one i wrote up even....9 times out of 10 ,when you disturb those lines, they leak and you won't find out until start up

 

Interesting question. However, there's only room in this forum for one guy who overthinks everything and tries to understand things that don't really matter. You're gonna have to knock me off my throne if you want to claim my title!

All seriousness aside, can you see any details inside the wet portion of the sensor? Maybe a thin rod centered inside a hollow tube? Does the outer tube have drain holes? If so, the sensor probably operates on capacitance. The rod and tube form the anode and cathode. The coolant is the electrolyte. When the coolant is low, that changes the overall capacitance.

In theory, such a sensor should last forever unless a film accumulated or some debris got caught between the two pieces.

Just a guess. Offered for free, and worth every penny.

 

you always amaze me Karl....yes , your attention to detail is worth every penny in my book

 

Thank you for that.

 

That is the detail I was looking for and thanks for the reply. That will help me with diagnosing the "little devil" Bob of Arizona

 

Got to thinking some more. The sensor in your first picture doesn't look big enough to work on capacitance. There has to be a fixed space between the two components.

My latest TheoryDuJour™, subject to wind direction and my medication levels, is a simple temperature sensor. When immersed in coolant, the temperature at the reservoir should be comparable to the reading at the engine.

Look at post #3 here, about halfway down, for a picture of the temperature sensors in the climate control system:

https://www.jaguarforums.com/forum/s...2/#post1714571


Does the tip of the coolant sensor look anything like that, with two wires in a shiny bead? If so, measure the resistance between the two contacts. Is it anything like 30,000 ohms at 77F? Apparently that is a standard for automotive temperature sensors. There's a chart with that picture at the link above.

I've looked all the training guides at Jagrepair.com, but none had any details of the coolant level sensor. I tried other models, too, but no joy.

Back to that crackpot capacitance theory, which is SO yesterday. Commercial aviation fuel quantity indication uses capacitance probes. Jet fuel always has a little bit of water in it, and it can throw off the quantity indication if a drop of water bridges the two halves of a probe. This would typically happen right after fueling, when the flight was ready to go. On the L1011 (giving away my age), the probes (a dozen or so per tank) were suspended from access plates on the top of the wing. For erratic quantity indication, the service manual instructed you to strike each access plate with a massive rubber hammer. This would knock the water droplet loose and the indication would return to normal. Talk about some strange looks from the passengers, though...

 

Hi Bob,

I'd have to dig a spare X350 reservoir out of the storage shed to confirm this, but I recall that the sensor is a reed switch. It is activated by a floating magnetic ring that rides on the outside of a cylinder molded into the reservoir. The magnet/float is in contact with the coolant and rises and falls with coolant level. The sensor/switch fits up into the inside of the cylinder and is not in contact with coolant. The sensor/switch is normally open. When the magnet floats at a level above the switch, the circuit remains open. When the coolant level falls, the magnet does likewise and activates the reed switch, triggering the Low Coolant warning lamp.

Here's a document I found with a quick search that explains the reed switch operation:

Littlefuse Reed Switch Coolant Level Sensor

This video shows the floating magnetic ring in a cut-open GM reservoir:


Cheers,

Don

 

Ahaa, got out my trusty dremel and removed the non-conductive cover to see what was inside. Not sure what the item is that shows up in the circuit? When I checked the two pins at the bottom with my multmeter, there was not a complete circuit. I checked and no coolant flows into the space occupied by the sensor. Looks like a metal tab is at the very bottom of the insert slot. Mystery to me? Thanks for your replys, very interesting.
Bob


end view With the black cover in place

 

That certainly looks like a reed switch to me. Does the reservoir have the floating magnet on the outside of the tube? Even if you can't see it, you should be able to shake the reservoir and feel/hear it.

If feeling adventurous, you could solder a new reed switch into that holder. They are not expensive at all. You'd have to play with a magnet to orient the switch correctly. No continuity = low coolant message? If so, you'd have to orient the switch so when the magnet (coolant level) is up, you have continuity between the contacts. You'd save a lot of money over the cost of a new reservoir assembly.

 

Hi Karl, I think it's just the opposite - when the switch is open, no warning lamp. When the magnet falls over the switch due to low coolant, the switch closes, completing the circuit and illuminating the Low Coolant warning lamp.

Bob, You may be able to test your reed switch by re-mounting it in the reservoir, orienting the reservoir so the magnet falls to its lowest level, then testing the sensor/switch to see if it is now closed (low resistance across its terminals indicating continuity). If your reed switch is working, the problem could be that the magnet is stuck in the reservoir or there is a short somewhere in the wiring for the sensor.

Cheers,

Don

 

Now my brain hurts, trying to do the mental aerobics. Thanks...

I was just going by his previous comments of having the message and finding no continuity between the switch terminals. Of course, that's with the switch removed, so there's no actuating magnet currently in play.

How about this, to be sure? Turn the key to run, with the vehicle plug still disconnected. That's the same as the switch itself being open. Then jumper the two contacts on the vehicle plug. That's the same as the switch being closed. See which condition turns on the message.

If indeed the switch is bad, check this out:

https://www.rockauto.com/en/catalog/...el+sensor,2184


Does that look like the same part? It's for a 2004 Range Rover.

OEM #PCJ500020

Standard Motor Products #FLS169

 

Wow...i am reimpressed with the knowledge available on this forum ...i now fully expect anything is possible on here

 

 

Bob,

What are you doing? Why aren’t you out in the garage, playing with a magnet and the reed switch, and posting pics?

Criminy, the suspense is killing us!

 

That metal dot doesn't move? a fixed magnet?

 

Thanks for that, quite good prices on Rock Auto.