Low Coolant light went on regularly after driving around 8 miles despite full reservoir. Tried new reservoir with sensor times two with no result. Yesterday my mechanic detached the ground plug and the low coolant light is now on continuously. Gonna take it to electrical shop this weekend but wondering if you guys can figure it out? Any help is appreciated. Thanks

 

There’s been a rash of bad sensors in reserviors. Simple float switch. Take it out, and check on table for continuity on electrical contacts when up and turn over in down position.

There’s a sticky thread video by Rev Sam

 

Have a look at this thread: https://www.jaguarforums.com/forum/x...cement-212844/

 

Remove the sensor from tank.

!) stick Neodymium magnet to sensor body. If Light goes out its the tank float.

2) Unplug sensor. short across the leads in the plug. If Light goes out, its the sensor.

 

I appreciate all of the advice but as I said I’ve already tried 2 new reservoir/sensor systems from different distributors from different parts of the country so if we assume that it’s not the sensor and remembering that once the ground was unplugged that the light has stayed on continuously, what is the next most likely problem?

 

If you’re sure the float sensor isn’t at fault check the wiring. Clean Connector first, then chase wiring to check continuity on the two ends

 

Did you even read the thread I linked to? This is a widespread problem with brand-new expansion tanks - where in the country you bought them is of no consequence. The light is supposed to be on when the sensor is unplugged - you need to bridge the terminals on the plug to put the light out.

 

BR 919 I had read the thread previously. I didn’t think that ALL of the new tanks were defective. Is there no place that I can get a new working reservoir and float?

 

If you haven’t physically checked the float switch, do that first. Easy check. See YouTube video.

Then check if bridging/ shorting the connector stops warning.

Report back with your findings and we can take it from there

 

Not all. but enough of the aftermarket ones are faulty that it wouldn't be a surprise to have more than one with a fault. I returned the aftermarket one and got a genuine Jag one which seems to have solved the problem.

 

According to mechanic both new reservoirs were ohm meter tested prior to installation and date of manufacture were two years apart.

 

Just out of curiosity, did you ohm out/check the original reservoir and compare it with one of the new ones? How does it compare?

 

My understanding the tank float is nothing more than a switch (on/off). Therefore only a continuity test is needed. It's not a float level/ohm relative reading. Hence the simple shorting of the connector to check warning.

 

The tank float has a magnet in it. When the magnet lowers down to the level of the sensor, the magnet causes the sensor switch to close.

Sticking a magnet on the sensor outside the tank should do the same thing, if the sensor is good.

 

My ohm meter (Fluke 77 multimeter) is one of my best friends when working on my cars, especially for voltage, resistance and continuity and as we all know, continuity testing is the act of testing the resistance between two points. If there is very low resistance (less than a few Ωs), the two points are connected electrically, and a tone is emitted. If there is more than a few Ωs of resistance, than the circuit is open, and no tone is emitted. Personally, I put my meter in to ohms mode to start as resistance measurements can be very revealing. When I can't see the meter, it then goes in to tone mode so I can hear it. Handy when I'm standing on my head trying to get the probes on a wire buried in the depths of the engine compartment. In my field in the good old days, we referred to this as ohming something out. I tend to ramble on, so, back to my original question: What did the mechanic get when he "continuity" tested the replacement parts vs the original? Did he test the bad sensor/tank? Did it or did it not have continuity? Did he check the connectors and cable? Be nice to know the cause before throwing new parts at it...

 

The original reservoir cracked mid Summer in Phoenix and the engine overheated and needed to be replaced. All subsequent reservoirs were brand new.

 

Even though the coolant expansion tank on my wife's 2006 XK8 is relatively new (sourced in September 2017 from rockauto.com), I inspect it every weekend as part of my weekly fluids-and-pressures check. You cannot be too careful with these Jaguar cooling systems....