Disco 2 2004 4.0 V8 overheating, overpressured

Hi all. I have got an issue with my engine. Few weeks ago my coolant started boiling. I've done a co2 test and it was present in coolant- my first call was head gasket. Done the job, took both out, took them for skimming and pressure testing, put new gaskets, new thermostat, water pump, expansion tank cap (just in case it wasn't releasing the pressure correctly) and put everything together. After starting the engine everything was fine until got to the right temperature and started boiling again. When I turn the car off the large amount of coolant just shoot out from opened expansion tank- very high pressure. I've done the co2 test again...the gas is still present in coolant. Can anyone confirm what's the next thing to check? Is it cracked block or slipped liner or something totally different?

So overheating so u replaced the iffy gaskets and then new thermostat,waterpump, expansion tank cap and still overheating so I assume that the viscous coupling on the cooling fan was functioning fully, what the reason for replacing the water pump?

Unfortunately while the V8 is a very good engine being all alloy they don’t take to overheating, if just the head gasket/s then u got of lightly but it’s a known fact that in serious cases a cylinder liner can slip in the bore, if so of course that’s bad news, It’s something that can be checked and seen once the heads have been removed and the engine is slowly turned over, so hopefully that was done at the time and all appeared okay.

If a liner is loose it also can be heard with a loud click, look on U Tube as there a demo shown where u can hear the exact sound made.

Forgot to say I also replaced the viscose fan, complete, genuine with clutch. All the parts used were genuine as well to avoid any future problems. I just thought while going head gaskets I would replace everything which could go wrong, that's why the water pump was replaced as well.
I did check the liners, were looking ok, but you're never 100% sure, I guess.

I think it could be that, the worse case scenario..I will try to find new engine then.

Perhaps you have an issue with your radiator.

Western Slope Rover said:

Perhaps you have an issue with your radiator.

Click to expand...

Will that cause the co2 presence in coolant system?

I had the same circus about 8 months ago.
Had just done the whole job after a small crack in the thermostat . Well I did not replace all the stuff you mentioned, just the thermostat and did the heads.
Just my luck, since instrument is useless I noticed a tad too late, my radiator gave up the ghost and it all bubbled again.

I searched high and low, put this time a new Nissen rad in, nice fresh coolant after driving for a while with water since I was topping up all the time.
Never drove without the Hawkeye so that I could see the real temperature .
I needed my car and yes it gets really hot here.
So I decided to put a decent fan in the front, fiddled it to switch on @ 84º and off @ 80º with an adjustable switch
I also asked our welder to make a bigger stainless expansion tank.
Now I can drive for hours @35-40º in the day and it never bubbled again.
I have done the same since for 2 clients, a v8 and a v6 Freelander . Works.

Oh dear

for my 2 cents... I say radiator blockage.

A radiator blockage would be great, but won't explain a failed gas test

Co2 is burnt gases, right? So how could that be caused by a blocked rad?
For my 2 cent's worth, I'd be looking at anywhere where exhaust gases could possibly come into contact with the cooling system. You seem to have done all the obvious stuff.
(The pressurising could be caused either by the coolant being too hot and expanding or by the injection of exhaust gases under pressure, or both.)
You skimmed the heads but not the block, so it possibly could be that but for my money it is looking like slipped liner/porous block. You can get top hat liners fitted I believe.
Poor you. My sympathies.