Range rover 2002 model 4.4i petrol engine, every 50-100km, losing 2litres water needs constant topping up. no sign of leaks around head gasket or rad. Inside carpet is dry so not heater matrix. what is causing the leak of coolant?

when you say replaced the top, do you mean the head gasket ? if so have you retightened the head bolts as is the normal process , if the leak and power loss is still there after checking head bolt torque then will probably need to renew the head gasket again and check for anything that might stop the gasket sealing correctly

This is common issue early sign head gaskets failure for EJ251 SOHC engine for external coolant leak. Second gen 96-99 with EJ25D is worst because when head gaskets failed, it's an internal leak that allows coolant and oil mix together in the combustion chamber to destroy engine.
You can drive it for at least 6 months or more as long as you keep top up coolant since the leak should be small at a slower rate leak. I drove mine for a while before change head gaskets. You're looking at `$1000-1200 job a dealership since you might as well change the timing belt, water pump, idlers while engine is pulled to replace head gaskets.

The coolant can only go in one of two places - either onto the road or into the cabin via a leak, or through the engine. Look all round the back and under the motor to see if coolant is leaking anywhere - especially from the valley gasket, radiator hoses, heater hoses, heater core etc.
If no leak is evident, it has to be a head gasket or worse. Make sure the engine does not overheat or a slipped liner may result - thousands of dollars.to fix

Leaking from where and how bad is the leak? If only minor, get under the vehicle and check for signs of leakage at the drain plug and around the oil filter - these are the most likely culprits. If not obvious, clean everything up, drive and look again.
If these places are not the source, (assuming this is a petrol model) look at the rear of the engine from the top and from underneath in case it is a leaking head or valley gasket

Could be a clogged radiator but most likely a failing head gasket. Inspect the drivers side of the head at the corner nearest the firewall. This is a well known weak spot in many of the engines of this era. Any signs of leakage at any time over the years is a tell tale sign at this spot. The pressure builds when the water passwordng through the engine is superheated as it passes an area of failure of the head gasket or warped head. Not an extremely difficult repair for someone with moderate mechanical skill and experience. Systematic teardown and reassembly after having heads milled. Bad news is that the superheated water takes very little time to damage your block beyond repair especially in the P38. I've been thru it a couple times and even the testing is costly. If you are extremely attached to this particular Rangie buy a new or professionally rebuilt engine otherwise you'll be chasing your tail and blowing a lot of cash in the process. Crates engines, rebuilt to factory specs and thoroughly tested with warranties are widely available on the www starting around $2000+shipping. Good luck. If I can be of any further assistance feel free to repost any additional.

Would advise getting cooling system preasure tested. loosing water indicates external leak. could be in heater box or pin hole in a hose. preasure will find it

pressure test radiator by colour check system ,or check for petrol vapour in header tank or radiator, check oil in engine to see if it is contaminated with water oil ,could be leaking rocker cover gasket causeing plugs to missfire if gas, petrol smell from water its head gasket ,water in oil headgasket, oil in water headgaskget if any of these requires head skim and head pressure test by a engineer

Hi could you try doing this:
get the engine warm then turn the heater on to its hottest setting then turn it on, if you only get cold air then this points towards the thermostat staying shut and if this is the case it will need replacing before you do any damage to the cylinder head and or cylinder head gasket.

if you have hot air coming out the the problem could be one of the following problems.
1, check for any signs of leaking coolant if you have a leak then this lets air into the system causing an air lock this stops the water pump pumping the coolant around the system and this prevents it from cooling, the leak could be either split hose, damages rad or leaking water pump so have a good look around all the engine and pipes looking for leak, the water pump is located where the timing belt is so have a good look around here.
2, water pump could be damaged and may need replacing.
3. worse case you head gasket could be damaged, if you find no leaks ant the thermostat is ok then your going to need to get the head gasket checked your car will need taking to a garage to have a color test done this checks the coolant for signs of engine gasses and if they are found it indicates head gasket failuer.
it will cost next to nothing for them to do this test.

if it is the head gasket then you need to find out what caused the head gasket to fail, it could have failed on its own or the water pump or thermostat could have caused it to fail.

check the oil for signs of water if you have a white substance if the oil filler cap then this is a sign water is getting into the oil via the head gasket, also check the coolant for the same signs of a white substance this indicates head gasket failure and the only solution would be to have the engine re-built to replace the cylinder head gasket.
this is a big job to do

let me know how you get on or if you need further assistance ok

This sounds like a cracked block, or blown head gasket.

I’m happy to help further over the phone at https://www.6ya.com/expert/jeremy_69f3cc28d95bf514

is there any water coming out the exhaust when driving under load if so the head or head gasket has gorn Lindz