Rav 4 2004 2ltr petrol, leaking coolant cannot find the leak, over heating, no hot heating, but will heat up when I've put more coolant in, no white smoke, no milky oil, no oil in coolant

If that was the only change that was made to the heating system by adding a stop leak then very probable that a part of the heater core has been plugged up with the additive. Unusual that it would affect only one of the vents but quite possible. There is not a way to change the heat level to individual ducts on that model vehicle mechanically.

no its the antifreeze leaking and drying out in the heat of the engine ,repair the leak --

Unfortunate you're losing coolant into the cylinders, where it's being burned off and exiting out the exhaust. When you initially added that cold coolant into the hot radiator, and hot engine (sit down) you likely cracked the engine block. Best case you just need to replace the head gasket.

check to see if your heater core is hooked up sometimes they leak,and owners bypass them.

Sounds like the water pump has failed. They do leak when bad, and they are located on the front of the engine. Be careful of overheating the engine till you get the leak stopped.

No heat is meaning the coolant isn't circulating, so it could be a few things.

1. Thermostat stuck closed (Most Likely)
   
2. Water Pump leaking
   
3. Clogged Heater Core
4. Intake Gasket Leaking Internal or External
5. Head Gasket/Gaskets leaking external .. If its internal there would be big piles of white milky smoke
   

there are only three places for coolant to leak.external leak to the outside of the motor,internal leak like a head gasket causing the motor to burn coolant(white smoke out the tailpipe),internal leak(coolant leak into the motor oil.)you say that the head gasket was tested and it was okay then this takes care of burning coolant,however it could be leaking into the motor oil.check the oil level and condition.I would think the tech would have checked this,but check it just in case.if the oil level is good and not thick or white or milky looking then this is not the problem.you could have a leak externally like a hose leaking a frost plug leaking,water pump leaking,this should be checked out by having the cooling system pressure tested a carefully inspected for leaks

Has to be coolant ,not water, water evaporates, if you use coolant and there is no leak, then the head gasket is damage or the cylinder head is crack. remove the spark plugs and check inside the spark plug hole for coolant, check the plug for wetness or white crust sign of burning coolant. good look friend.

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It appears that you have a minor leak at where a hose attaches to an engine or radiator pipe. When the engine is hot, any small leak will evaporate quickly and therefore not be seen. As the coolant heats up it will expand into the overflow tank but once the engine is stopped the extra heat build up will force the coolant out the leaking joint. As the engine cools, the leak prevents the coolant from being sucked back from the overflow tank.

Check all hoses and clamps including heater hoses and those pesky little bypass hoses in the cooling system for a good tight fit and replace any hoses that have gone hard or have become soft and stretched. Those spring type hose clamps tend to be less effective in clamping as the hoses age. Worm drive ones are the best to use.

If unsure take vehicle to a cooling system specialist and have them do a pressure test and more thorough diagnosis.

If problem persists, then it could indicate a problem with the head gasket (Usually caused by allowing engine to become excessively overheated when cooling system has run dry) allowing very hot high pressure combustion gases into the engine water jacket, which super heats the coolant in the engine block, which then boils off, and is released via the cap or any leaks. If the head gasket is really bad it will leak water into the cylinders and into the oil in the sump. This is indicated by an emulsion of water and oil mix on the dipstick. You will also see white smoke (water vapour) from the exhaust.

replace your radiator cap.