Outer Limits 4x4 Board

Ever since I bought my GQ (TB42), when I'd turn the heater on, I had a slight coolant smell. As the car wasn't overheating, I didn't worry too much (although I kept an eye on the coolant level, and had to give it a little extra every now and again. Fast forward to a ouple of weeks ago...Was driving up to Echuca, and when I got there, everytime I'd turn left, I'd get a wet left foot. Looked at the bottom of the heater box, sure enough, a pool of coolant. Found time this weekend to take out the heater core (which involves taking out every other bloody piece of the car first...!), but I can't find a leak in it anywhere. Tried plugging up one copper tube and blowing into the other while the heater core is underwater, no bubbling. Then tried sucking on it and sealing the hole, and connecting a vacuum gauge to the other end - seems to hold vacuum at 30in Hg (about 15psi). Anyone have any other ways to test it? If I take it into a radiator shop, will they be able to give it a proper pressure test? I don't want to put everything back together, to find leaking coolant again.

Could be in rubber hoses to core or maybe the heater core only leaks when hot.
You could try putting hot water in it out of the jug then pressure test it

Yeah, all the hoses etc, are still connected. Tried the same test, underwater in hot water, and filled it up with boiling water (burnt my tongue too, cos I'm a spaz). Still couldn't get it to leak. Hopefully a radiator shop can test it better than I can.

Got a radiator shop to pressure test it. They couldn't find a leak, but as it is such a pain to remove, decided to buy a new core anyway. Likely that an internal O-Ring in the tank is stuffed.

Thanks for the help.

I hope that sorts it for you.
Nothing worse than finding out its some 2 cent part after you spend the big coins. ( Been there done that)
That said, I agree with your decision to replace it due to the PITA it is to access

Just had a thought, is the heater tap part of the core or is it separate? Is it under the dash? I have had a few of these give troubles over the years - not in a Patrol though