Coolant bubbling and spewing

[drummerboyXJR]

Yet another problem, after a 'spirited' drive, my XKR spits out water from the expansion tank overflow pipe (just behind offside front wheel). Not a huge amount, but enough to create a puddle. Can hear the coolant bubbling and boiling in the expansion tank for several minutes after switch off. Temp gauge never goes above half way however. Any ideas guys??

[peterzoom]

I have had the same problem, exactly! When it first happened it really had me worried and I went straight to the main dealer. They diagnosed that the small black plastic hoses you can see, beside each other, at the pressure cap, were transposed. So they swapped them round and fitted a new pressure cap also. I then marked one hose and its location with a spot of white paint to prevent any chance of this mistake ever being repeated.
Result.... 10 times worse!
So I reversed the hoses, adjusted my marks to suit, carry a bottle of ready mixed long life coolant in the boot and just top up if it occurs again. Not that it does every time I exercise some heavy right foot! Probably only have to top up once a month. It is annoying and it would be fantasic if anyone here can shed any light on the situation.

[Fullmel]

It's not That uncommon for the head gasket to go.

[drummerboyXJR]

HGF was my first thoght but have none of the other symptoms

[Simpo Two]

I have a hunch that Jaguar temp gauges always say 'halfway' regardless of what's going on....

[Scotty2]

Try adding "Barrs Leaks".

Guys I worked with always added that to race engines as it will stop and prevent a weep or some porosity but not a blown gasket.

[drummerboyXJR]

Ok, update. just let it warm up from cold. Temp gauge never goes above half way, but no sign of fans kicking in even after 15 mins running. Expansion tank very hot, and coolant starting to eject from the overflow pipe. Top and bottom rad hoses nice and soft, not full of air. No white steam from exhaust, no sludge in filler cap, no smell of exhaust in expanion tank. Ticks over perfectly, no rough idle.
Any other ideas guys, thermostat not opening fully perhaps?
Have booked in for a coolant sniffer test on Monday, am keeping fingers crossed!
Thanks

[x type]

My old Audi coupe did exactly the same

Radiator was blocked ,tried flushing it out, no good

New rad was the answer

Edited by x type on Friday 10th September 21:12

[Piersman2]

my old xjr used to do this. It would overflow the expansion bottle. I would fill it up, it would overflow, repeat.

Turned out to be a slightly split hose between the tank cap and the expansion bottle.

Basically when the fluid was hot it would expand and fill the bottle. As it cooled down again , the small split in the pipe, would allow air to be sucked in rather than sucking back the fluid from the bottle.

Took a while to suss that one as the pipe looked fine enough.

[drummerboyXJR]

Thanks Piersman, i'm liking that sort of answer!

[drummerboyXJR]

Just an update, took to local diagnostic garage, did the hydrocarbons test in the expansion tank....few anxious moments.....yeh! the fluid stayed bluer than a blue thing. Absolutely no gases in the water, lovely.
Then he gets his heat sensing gun, engine side of stat reading 88 deg, rad pipe reading 60 deg. i need to get me one them there thermostats!
Thanks for all your help guys, a £20 fix, rather than a head off nightmare bill.

[Fullmel]

Glad to hear that.

[slippery]

Bizarre! Mine's in the garage for the same sort of reasons, the cap on the expansion tank was letting off a bit of steam but no other problems. They are fitting a new cap and thermostat as we speak and I'm hoping all will now be well!

[drummerboyXJR]

Aha, drip..drip..drip. Just an update to my spewing from overflow problem. Changed the suspect thermostat, no difference. Have just noticed a little drip of water from the connector between the big ally pipes by the supercharger pulley, and a thin black plastic pipe going to the expansion tank. Could this mean air is getting in there and messing up the expansion/contraction thingymajig?
I dont quite understand the theory involved with pressurised systems, but if any experts can help please? Obviously there is a little leak which shouldnt be happening.
Many thanks

[drummerboyXJR]

Right, have cured the little drip from that connector, O ring was gunked up. Still spewing. Have noticed some steam from the Rad, even though the temp guage never goes above halfway. Rad is boiling hot, thought it was just steaming off the rain water from last night, but has been doing it for 10 mins now. Any other ideas guys, blocked rad perhaps?
Thanks

[RW774]

Hi Drummerboy, if the head gasket has a slight weep around the fire ring directly into the water jacket, everytime the piston comes up on compression it increases the inherent coolant pressure as the compresion in the coolant system builds , all too quickly.Hence the fact that its` building pressure before the engine has a chance to heat up . A block test is in order, which will confirm whether the coolant system has combustion gases within, which if positive, will be a headgasket failure. Cost of block test, £49 plus vat

[drummerboyXJR]

Hi RRW, have had a block test, its fine, stayed as blue as a blue thing, as i mentioned earlier. Had temp sensor on stat and it looked like stat wasnt opening fully. Changed stat, still the same. The steam from rad is wafting up from all over the rad, not just one place. Gauge never wanders over halfway though.

[RW774]

Hi Drummerboy, pressure test next when hot.The water in the header needs to be kept low otherwise the blocktest will be contaminated by the coolant, not an easy thing to do on a V8 as the level rises quickly in the header.

[slippery]

I had a supposedly clear test done on mine a few days before another one showed it clearly wasn't!

Edited by slippery on Tuesday 28th September 07:46

[drummerboyXJR]

The block test guy sucked the tank empty first with a pipette, so only the gases were being drawn into the test fluid.it runs a dream, pretty sure its not hgf. What about a the expansion cap, do ther ever fail? Cheers