Sounds like you have similar problem to me. For weeks Ive been bleeding and have changed the water pump, stat, radiator & hoses. I did a block tester several times which showed negative but my coolant was still blowing out, anyway , Im half way through doing the head gasket as thats my final option but it looks like you are actually finding a few faults whereas Im just hoping still.

Just had a thought.
What about using an impact wrench. I have one that tightens to 340Nm so in theory it should be capable of loosening the same.

Chris, You saw past my ignorance in using a 3/8 as I DIDNT get past the first bolt not that I only have 1 bolt left.

Richard, Thats a long bar. Mine is only about 2ft but I have a longer one on order along with a Stahlwille 3/8 to 1/2" adaptor and a 1/2" powerdrive impact universal joint.
Ive managed to clean the rockers, they were surprisingly easy to clean.

Strange that both 16mm & 5/8 are not a perfect fit. My 16mm broke and after finding my nice set of impact sockets the 5/8 is a 1/2" drive but my wrenches are all 3/8 so yet another item to buy and wait for delivery from good ol Amazon along with a longer breaker bar.

Attempted to remove the cylinder bolts and haven't even got past bolt 1 yet. It is not budging , broke a socket in the process.
Just waiting for some more penetrating spray but will buy some decent sockets in the mean time.

edit Just remembered I have a lovely impact socket set that I've never used, haha.

Ha, I thought you was going to say, if it was yours you'd set fire to it or something. I will soak them in diesel in that case but is it safe to clean the valley.

Whats the best solution here. Buy new rockers/pushrods etc or try clean it and if cleaning will work whats the best method.

So far its going quite easy.
Taken the valley gasket off , next is to tackle the exhaust manifolds which is probably the most difficult going by what people say.

My rockers are absolutely gunged up with black sludge and some of the other hoses need replacing. The coolant hose from the bottom of the expansion tank to the throttle body just snapped off in my hand but it was one to replace luckily.

Just waiting for this sodding rain to stop, its relentless.

Thanks for the tips already.

As you all know Ive been keeping you all busy helping me with my overheating problem which I really appreciate but after weeks and weeks of agonising over the cause and changing costly parts I have decided to go with my gut instinct and strip down the engine as Ive probably spent €100 in coolant alone and have bled the system till I was blue in the face.

I have found what appears to be a very well put together detailed blog on how to do the head gasket should I get that deep in stripping it down called Paulsp38.com

http://paulp38a.com/range-rover-p38/engine-refresh/

Anything you'd like to add in making it easier or recommended parts is obviously appreciated .

I have to laugh or I'll hit my head against the wall.

After yet another attempt at bleeding, my top hose has developed a hole. Its caused by it rubbing on the serpentine belt where ive been squeezing it so much it was making contact and worn away.
So another 5 days of waiting for a hose to arrive.

So could I be right about the inlet manifold gasket, maybe sucking air in?

It usually blows out and overheats when driving.

Whilst sat outside with the cap off its just blowing out but I probably also dont give it time to overheat as I turn it off straight away.

The other day when I thought it was fine, whilst sat outside with the cap on it dribbled out the overflow but didnt overheat until I drove it.
I also have had the engine revved between 2-4k whilst outside without blowing out therefore thinking it was good until driving again.
On the odd occasion whilst overheating the needle dropped back down which made me think maybe it was a doggy thermostat before .

When I hear the engine gurgling once its blown out its gurgling from the Inlet manifold ( from 99my) or the bunch of bananas as someone else calls them. Is that where youd expect to hear it . I'm wondering if air is being sucked in through the gasket. I replaced the gasket last year and it was a bit tricky seating it, just wondering if that could have anything to do with it. You can tell I'm not afraid to look stupid :)

Thanks OB for keeping me going. The plugs if anything where sooty probably because the O2 sensor needed changing.

I have pretty much done that routine with raising the tank etc. I thought I'd cracked it the other day as I ran it for ages even with the cap on without it overflowing but 5 mins driving and it overheated.
I did have it on ramps when it was ok, it seems to be when its on the flat or maybe just driving I got the problems apart from today where its constantly overflowing without the cap on even.
I will give it one more go tomorrow but this has been going on for weeks if not months now.

Well so far I have changed:
Radiator. Water pump.
Thermostat.
Hoses.
Expansion cap.

It seems even worse now. It now overflows with the cap off , It only did it with it on before. Ive bled and bled and bled.

Still no indicator of gas in the coolant using the sniff tester or mixture of coolant with oil.

Its time to strip the engine as Ive probably spent near £800 on replacing other stuff the past few months otherwise I would probably just give up.

Just removed the radiator as my new one should be arriving today.

You were probably right Gilbert, The only label I can find on its is BTP53695 or something like that so its probably a Britpart, it also has a lot of damaged fins which would have been there from installation. Yet again French cowboys at their best.

Still not feeling confident this is the end of the problem though, hopefully the new one will be here soon.

Sounds highly probable.
Its been cats n dogs for weeks here now. My sunroof drain also needs doing.

Not the Thermostat, just took for a spin and quickly overheated. The bottom hose was still cold so I guess its a radiator change.

My MPG has dramatically dropped to 8/10 mph though the rear exhaust is corroded according to my last MOT.

Had a closer look at the passenger leak and the OBD is soaked but its water and not coolant and the same thing happened could here the whining wooshing noise and a jet of water.

Its shot out of the top r/h corner of the passengers footwell, I havent managed a closer inspection yet as its been chucking it down for days here.

Fitted new thermostat today, only took 11 days of waiting for it to arrive,tut.

Its looking hopeful though the proof is in the driving which I havent done yet.

I ran it for 30 mins with a lot of high revs, No overheating and the needle sat nicely in the middle, soft top hoses BUT it did drip from the overflow pipe then slowed down and eventually stopped overflowing so I'm hoping that was just it settling in or something with the correct amount of coolant.

As usual fix one and another appears or it maybe related.

As soon as I turned the engine on I heard a fast whooshing sound , it was coming from the passenger side blower area and a fast pressurised jet of water was pissing on to the carpet, probably half a cup full. It then stopped.
The only thing that Ive read it might be is the A/C drip tube is blocked and is backing up but would that cause a high pressure jet or is theer anything else behind there?