I have heard this story several times now.

Your low coolant light goes on. You think, 'ahhh, it probably just needs a top up, I'll take care of it later'. You continue driving. A few miles later your engine just dies. You have it checked out and you find it had overheated. You never recall seeing an overheat warning or any steam. Your engine is now beyond reasonable repair.

This happened on my wife's S-type a few months back. I have since heard the story several times from others.

What happened? Why did you not get an overheat warning?

The fact is if you have a major coolant loss, such as due to a ruptured or disconnected hose the coolant can get quickly pumped out as you drive. On a Jaguar the coolant sensor is in the upper part of the engine. If the coolant level is low enough, the sensor will not be immersed in coolant and will never see the overheating condition!!

The moral: NEVER ignore your Low Coolant indicator. If you have a slow leak, get if repaired ASAP. If you get in the habit of ignoring your low coolant warning the results could be fatal for your engine!!!

 

Luckily, I intuitively knew that. A friend of mine has a very nice restaurant on the waterfront and has a sort of mini festival each year with three different bands and various food booths scattered across the property. It is really quite a nice event that I try to never miss. A couple of years ago, I was on the way there and just a few miles from home got that dreaded warning. I pulled over and checked the level and could still see some water in there, so it was not really gushing out, but I turned around and immediately went home and missed the event.

Any time an engine is susceptible to overheating it is imperative to take care of it immediately, and, as I understand it, even more so in the case of our Jaguars.

 

+1

Beats disintegrating tensioners for the biggest and quickest engine killer.

Graham

 

I did a lot of investigating as to how the low coolant tempertature probe worked when the magnet popped out of the float in my expansion tank. The expansion tank holds almost a quart of liquid. The float sits on the bottom of the tank around a cylinder that is hollow but sealed on the top. The sensor probe sticks up inside the hollow cylinder from the bottom. When you fill the tank the float only rises less than one inch before it stops. That small rise is enough to activate the sensor probe and close the circuit that turns out the warning light for low coolant. There is a lot of coolant above the float at this point. Therefore you must loose almost all of the coolant before the float will drop enough to cause the sensor probe to open the switch and indicate low coolant. When that warning light comes on you had better stop NOW. Let the engine cool and check the tank which is probably empty. It will not be just a little low.

 

Mine used to set off the light if the coolant dropped as little as 1/2". Since repairing the little crack and cleaning the sensor I don't get that anymore...even though I know there's still a tiny leak from underneath (just enough to smell it and leave a stain on a white paper towel when I wipe under).

The light hasn't come on during this trip so I think I'll open it up and check. Thanks for the reminder.

 

I unscrew the coolant expansion tank cap and check the coolant level every weekend. It's just an automatic part of my weekly routine fluids checklist for all of our vehicles. It only takes ten seconds to check, so why not go ahead and do it? It's just common sense based upon the nightmare stories here telling of rapid coolant loss followed by almost instantaneous engine destruction....

So check your coolant expansion tank level every week. You'll be glad you did....

 

I actually keep fluids with me at all times along with a tool kit in all my cars. It sounds paranoid, but doing so saved my Corvette from needing a head gasket.

The XK's trunk that lifts up has been nice, nothing visible until you lift it up. I keep a quart of oil, a half gallon of ready coolant, a sealed container of brake fluid, a sealed container of PS fluid(qt Dexron III) and the Mercedes dipstick (if I'm low, it's getting towed home). This is all around the spare tire (donut). On top of the spare tire is a small 100pc, metric and standard wrench, socket and ratchet set (3/8" and 1/4") that also has a bit driver with plenty of bits. There is also a small bag with standard+needlenose+channel lock pliers, vice grips, a cutter/stripper tool, an OBDII Scan Tool (not code reader, scan tool) and assorted other tools.

It sounds like a lot, but it's nice when you're on the road and a tiny problem stays tiny. I think everything tool wise, excluding the scan tool($200 for XKR and Aurora, $500 for netbook and cord for A8), is about $200-300. I have fluids and tools similar to this in every car as I know it will be money saved if and when stuff breaks.

 

On the 2003 XK8, upon start-up the system check screen gives the "Low Engine Coolant" message. I bought the Jag in May 2010 .. have seen this message 3 times so far .. maybe 6,000 miles driven tops .. 81K now.

The 4.2 is supposed to use the "long life" anti-freeze .. I probably should get some, but so far, maybe a cup of distilled water brings it right up. Amazing how sensitive that sensor is. So less than a quart in 6,000 miles is acceptable I guess, but it does beg the question .. where did it go .. guess that's being pedantic .. lol.

Having owned Ford trucks for the last 35 years, the water pumps are good for 60,000 miles .. just like clockwork. Glad there's no crossover .. the status display is awesome, and I Do pay attention. If there is a warning light somewhere .. I missed it.

 

Yes, it is a message. Thanks for the clarification...I edited the original post.