Unusual coolant loss from Jaguar 3.2 V8 2000

[v12vandenplas]

Just bought a 3.2 V8 which runs perfect except for when you switch the car off you get a boiling sound like a kettle from the NSF wing and then huge amounts of coolant expelled from this area, this car does not overheat when driving, temp is rock steady, no loss at all whilst running, have driven non stop 186 miles with no issues at all but when you switch off this mystery bubbling begins, can anyone help?

Thanks
D

[Jaguar steve]

The X308 temperature gauge is software driven and not always an accurate indication of actual coolant temperature.

What you are discribing is excess heat or pressure in the cooling system forcing coolant into the expansion bottle under the nsf wing. That's now full and excess coolant has nowhere to go apart from onto the road. Potential causes include an airlock in the cooling system, failed headgasket or localised overheating somewhere.

Cooling system is under pressure once warm or hot. Don't undo or remove anything, you will get scalded.

Several things to check to help diagnosis.

Coolant level when stone cold. Should be almost at the top of the header tank.

Do the radiator cooling fans work when up to temp? Checked the fuses?

Is the thermostat stuck? Start up from cold and hold the top hose for several mins. There should be a quick sudden increase in temp when the 'stat opens if its ok. If it slowly heats up from go the 'stat is stuck open. If it never gets warm it's stuck shut.

Is the waterpump knackered? There should be a steady stream of coolant back in to the header tank - check this only when stone cold by removing the cap and running the engine at 1500 rpm or so.

Does the interior heater work? If not either the circulation pumps packed up or there's an airlock.

Does the coolant smell burnt or gassy?

Lots of fine bubbles in coolant stream?

Feel all the accessable hoses. None collapsed internally?

Whatever you do don't ignore it and get it sorted asap. There's potential to blow headgaskets very quickly with any cooling system malfunction.

HTH

[P700DEE]

Comprehensive response from Jaguar Steve but I think he missed another. You can get this if the radiator cap is faulty. Try swapping the cap.

[Jaguar steve]

P700DEE said:

Comprehensive response from Jaguar Steve but I think he missed another. You can get this if the radiator cap is faulty. Try swapping the cap.

Not on the X308 but I guess I know exactly what you're refering too. That's the old technology spring loaded caps that were actually on the radiator filler neck. They'd certianly leak - as they were designed too - to relieve excess pressure in the cooling system. If one went faulty, usually by the spring loosing it's rated lift pressure then they'd leak a lot more than they were meant too

On a sealed cooling system like the X308 the theory is over pressurised coolant is vented into the sealed expension tank. You can compress a gas but you can't compress a liquid so filling the tank with coolant reduces the available volume and therefore pressurises the air above the coolant. As the engine cools that air pressure ought to force the overflowed coolant back into the header tank.

If the tank is already full or there's way too much pressure in the cooling system that won't work - hence the coolant pissing everywhere.

[v12vandenplas]

Thank you very much for the info and recommendations, I will look and try each one suggested, and let you know how I get on.

Cheers
Danny

[Piersman2]

I used to have 1998 XJR that dumped excess water out of the expansion bottle, but kept prompting me to top up the water as well.

After investigating it for some time I sussed out the pipe between header tank and expansion bottle had a split in it.

Hot water would expand filling the bottle as designed. But as it cooled, the split in the pipe would allow air to come back in the system rather than sucking up the expanded water in the bottle.

So I'd get a message regularly about low coolant, top it up, and it would expand into the bottle to not be able to come back. Eventually the bottle filled and would overflow as the topped up water expanded into it.

Replaced pipe, sorted.

[v12vandenplas]

Hi there, just checked the following from your questions;

Coolant level when stone cold. Should be almost at the top of the header tank. ONLY GOES DOWN WHEN COOLANT LOST WHEN ENGINE IS SWITCHED OFF, BUT NOT ALL THE TIME, JUST HAD IT RUNNING NOW AND NO PROBS AT ALL BUT DID HAVE CAP ON AND OFF A FEW TIMES TO CHECK...

Do the radiator cooling fans work when up to temp? Checked the fuses? ALL FANS WORK

Is the thermostat stuck? Start up from cold and hold the top hose for several mins. There should be a quick sudden increase in temp when the 'stat opens if its ok. If it slowly heats up from go the 'stat is stuck open. If it never gets warm it's stuck shut. OS PIPE GOES HOT QUITE QUICK, ONE TO NS OF RADIATOR TOOK SOME TIME AND NOT SUPER HOT

Is the waterpump knackered? There should be a steady stream of coolant back in to the header tank - check this only when stone cold by removing the cap and running the engine at 1500 rpm or so. WATER COMING THROUGH AND VARIES FLOW WITH RPM SO OK I GUESS

Does the interior heater work? If not either the circulation pumps packed up or there's an airlock. HEATER WORKS SUPERB

Does the coolant smell burnt or gassy? NO SMELL OF GAS OR BURNING

Lots of fine bubbles in coolant stream? LOOKS PRETTY GOOD, NO BUBBLES THAT I CAN SEE

Thanks for your advice and help
Danny