My overflow tank (2003 XK8) is topped and the system holds pressure with no sweet smell evident. After the car cools and I remove the cap and use my wire probe to move the float up and down, the message disappears. After reading Gus's narrative, perhaps the sensor, float or both are fouled by lime or other chemical. Would you expect harmful effect if the tank was removed and flushed with 50/50% vinegar and water solution? This should remove most contamination shouldn't it? What say ye?

 

The float is inside the tank, the sensor is outside. Your proposal might clear the problem if the float is stuck, which is common. Just rinse it thoroughly afterwards.

 

Consider a new coolant expansion tank cap as well. Yours may have failed. When they do, your coolant does not properly flow back and forth between the expansion tank and the atmospheric recovery tank. Coolant can also leak out around the cap seal no matter how tightly you crank it down. That is exactly what my wife's 2006 XK8's cap was doing a few weeks ago. I replaced it with a new one (about $18) and all is well again....

 

Thanks for quick replies, but I'm now a bit confused. Looking at the pics on Gus's procedure, it appears the float encircles the coolant level sensor (LNA740AB) inside the tank and moves up & down. Either could impede the movement and provide a false reading. I cannot visualize the sensor on the outside. Please correct if my perception is in error? I have made 1 mistake in the past 60+ years, :-)

 

I had been having the same warning on and off for a few weeks. In my case it was the sensor that was fault and was replaced for £12 for a good second hand one on ebay.

 

The sensor is installed into the tube that the float rides up and down on. The inside of that tube is 'outside' or maybe better described as isolated from the coolant as is the sensor.

 

Thanks for explaining the "Sensor" term . The tube that encloses the sensor is the item I tried to describe. The float encircles the tube with sensor inside. It rides up and down with coolant level providing the reading that opens and closes the switch. Guess it will not cause a problem if i use a mild solution to clean and flush the tank. Thanks again and the info from you guys is extremely helpful. SAFETY FASTER!

 

If you want to 'clean' it and are willing to remove it from the car I would use vinegar which is a stronger acid than a commercial coolant system cleaner. Certainly won't hurt the plastic tank.

 

While you have the tank off if that's how you'll flush it pull the sensor from underneath, it's snaps in/out but be very gentle the probe breaks quite easily and clean the probe as well, might give the connector a cleaning too.

 

I think it's more likely that the float has lost buoyancy than that it is gunked up with lime or something else.

There is a thread (somewhere) from a year or two ago where some of us worked on this. A fix is to make a little c-shaped floatation aid (a water bottle cap is suitable material if I remember right) that can be sort of snapped in place under the float to help it ... float.

If you do remove the tank, you might check for this condition before putting it back in place.

Good luck.

 

Update on Expansion Tank RESOLVED, replaced original with an A/M brand (URO) tank from Vendor on E-Bay. They sell OEM and A/M. The replacement was $95 incl S&H. It had new cap and sensor; ready to install. No more LOW COOLANT LEVEL message!

 

I replaced my coolant tank with sensor and cap with a part from SG Barret cot was 115US and took less than. Half hour.