97 Accord Overheat/Coolant Leak/Radiator Vacuum

Ok so I’m out of ideas here and thought I’d see if you could all give me a hand or some suggestions.
It’s 9am here (Sydney, Australia), my friend is leaving for a long distance drive (Sydney to Brisbane, approx. 9 Hrs) in 2 days time and I need to sort this out before they go… :-/

The car is a 1997 Honda Accord (Engine F22B3). Originally when first driving the car we found that the temperature took a long time to increase. After trying a few things I found the issue was the thermostat (All that was left was the housing/frame :-/). Replacing that the engine heated up normally. Next, driving along there was a leak and steam started bellowing out from under the bonnet. After 2 mechanics couldn’t figure it out I found it was simply a loose top hose :-/. Now comes the kicker…

Driving along the temperature gauge went all the way to the top which was obviously concerning. I found there was somewhere between 500ml to 1000ml missing from the radiator when I looked at it the next day after cooling down. This was quite concerning, considering I filled it up not 3 weeks earlier when the above issues occurred. Having said that, I took it down to an airlock scenario. However, checking it the next day after further driving found the level had dropped slightly again. Fearing it was a bleeding issue, I bled the engine again to ensure there was no air in the system. Further to that, I did a pressure test on the cylinders and found no loss of pressure, checked the oil cap and found no milky residue, pressure tested the system to 1.1kpa (Which is on the cap) and found no leaks. Further driving testing lead me to find a very minor leak at the hose connection to the radiator which leads to the overflow tank. This was concerning because my thoughts were the cap should open and close and it must be easier to get coolant from the overflow tank than to try to suck it through the little gap? Regardless, I put a clamp on that connection and it’s now secure. Checking the car this morning (It’s been a few days), I found that the overflow tank is full (I admit previously it was fuller than it should have been, but definitely not all the way up the top), and when removing the radiator cap there was a small vacuum pulling it down. Removing the cap I again found the coolant level was low and required approx. 500ml of coolant. Also just to note, I’ve checked the exhaust (Even though I pressure tested), and found some white smoke/condensation coming from the exhaust, however the car is parked outside and I believe it stops after the engine warms up so I’m assuming it’s condensation in the exhaust system.

So, coolant is leaking out somewhere, it doesn’t appear to be internal (Block or cylinders), and I can’t visually see any external leaks. If I had to guess right now I’d say maybe the 2nd valve in the radiator cap is bad? Allowing coolant to flow out but not back in. This I don’t think is an issue though because that overflow hose was obviously sucking in air at the time. The only other thing I can think of is maybe there’s an issue sucking in from the overflow tank? Now looking at the hose that leads down into the overflow tank there is a little bit of a kink in it so I might change it, but when I noticed the air bubbles on that hose/radiator connection before I removed the hose and blew on it and air did go out (I know that’s not the same as sucking it but I didn’t want a mouth full of coolant haha).

So at this point I’m down to changing the hose in the overflow tank. Based on what I’ve mentioned above, does anyone have any other ideas they could suggest or they may have seen with a car like this?

Cheers in advance all 🙂