Hi folks, try and keep this as detailed but as Breif as I can.

Got a 99 td5 disco, first bought it all was well, then the radiator burst, so I installed a new rad and thermostat,

All worked fine except it takes absolutely forever to heat up, bled it a million times. No air anytime I did.

Then the top radiator hose blew on a run back from up north, got it home thanks to the Rac. Fitted a new hose, a low coolant alarm and a digi temp gauge.

So I have been away working for 12 weeks, come back and got the landy from my work. Took it a good run. Temp wouldn't go above 52°c, but besides that. No probs. So I made my own radiator muff, went a run and it finally got up to 80°c stopped just for a look under bonnet for anything untoward and it was ****ing water out the overflow on the header tank.

So I fitted a new cap, just to rule it out. Took a good run. Got 70-80°c constant temp, but when I stop the heaters go cold until I either drive off or I give it a good rev, the top hose is absolutely solid, and when I open the header tank the return is a stopping and starting.

No oil in water, no water in the oil, no smell off gases from the tank but that's not to say there not there. Everything works fine apart from no heaters at idle and the fact the top hose is brick hard, and with engine off after a run I can hear the new cap slowly hissing away which tells me it's overpressurising.

I dunno whether to just rip the head off and do the gasket and dowels to be on the safe side.

Sounds like the water isn’t circulating, make sure the water pump impeller hasn’t fallen off

Whilst I don’t have the same history, I have very similar symptoms (‘53 Td5 Auto)

Rushing water sound from heater matrix when engine revved.
No heat to cabin at idle
Temp gauge bang on level (but don’t now trust that following responses to my other current thread)
Rock hard top hose
Hissing from header tank cap after long run
Regular bleeding (as per RAVE) and top-up
Little or no water in header tank until cap (pressure) released.
No obvious leaks from system.

Had new rad and hoses on a couple of months ago, and a chemical block test and pressure test at same time - all OK then.

I’m dropping her into my trusted Indi tomorrow morning for a look and see if there is a diagnosis. I’ll share the outcome with you once known, and see if it helps you.

Gut tells me HG, but equally maybe something more mundane like a failing pump, leak I can’t see, stat, blocked heater matrix. Clearly expecting the worst and hoping for the best.....

A static test rig should tell you straight away if head gasket is leaking.

As promised.... my diagnosis was either HG or cracked head. Monitoring oil levels between now and 16th when she is being fixed, see if it’s rising with diesel from cracked head.