I've just recently received a message advising me that my coolant level is low. Trouble is that the expansion tank is filled to where it should be, coolant circulates through it, supply and return radiator hoses are not 'squishy', temp gauge stays right where it always has which is dead center, engine fans cycle as they need to, water temp remains plus or minus 190, air conditioning fans run when compressor engages and no error codes show on my OBDII reader. I even let the car idle for 15 minutes or so in the hot sun on a 85 degree day (hood open) and saw no leaks, steam or temp gauge fluctuation. Just for giggles I disconnected the battery (engine off) for several minutes thinking that might erase the low coolant message. It didn't.
What's my next step?
Is it possible that my radiator needs to 'burp' because of trapped air?
I'm guessing the expansion tank level sensor (if that's where it's located) is stuck or more likely toast. Can the level reader be replaced or am I going to be expansion tank shopping? Any ideas?
Car is a very babied 2003 4.2 Jag XK8 with 46,200 miles on the odometer. I'm the second owner of this west coast car (bought it with 42,000 on the clock) and have had the car with no issues for more than 5 years. I want to sell it and get a newer one.

 

You’re right in that it’s probably a bad float sensor in the coolant expansion cap.

Good news in that it might just be a stuck float, and a pencil magnet may move it. Otherwise you’ll need to remove the tank (basic 10min DIY) and check continuity on the pins. Check upright, then check again turning the tank upside down.

if you’re ordering a new tank, beware as there’s been reports of a bad batch where the sensors are bad.

 

Is the float in the screw on cap or in the tank itself? I've got a pencil magnet so if the float is inside the actual tank I should be able to get to it. If the float is part of the screw on top assembly the job would be even easier. Before I posted my question I tapped the tank on all sides with an small upholstery hammer yesterday to no avail. Hope I luck out with the magnet.

Thanks,
RB

 

+1 with David. Hey a heads up if you replace the tank: the hard plastic tubes out of the tank that run across the valve cover area are very brittle and unless you are lucky they will brake on you.

Point of story - have rubber tubing and small clamps on hand to mend a brake, just in case. Super easy fix, cost <$2.00. Good insurance IMO unless you live next door to auto parts store :-).

John

 

[QUOTE=DavidYau;2108155]You’re right in that it’s probably a bad float sensor in the coolant expansion cap.

Good news in that it might just be a stuck float, and a pencil magnet may move it.


Pencil magnet made my expansion tank a happy camper once again. Low coolant message gone.

Thanks David

Best,

RB