I have my radiator out of my car laying on the ground and I had filled it with vinegar to remove the white calcium buildup at the ends of the cooling tubes. After soaking for a week the calcium buildup is soft but it did not disolve.
Is there something better to use ? Lemmon juice with the vinegar ?
(the engine is out right now being rebuilt )

I'd turn the rad upside down & reverse flush it hard in that nipple with a garden hose/nozzle but I'm afraid it's going to take something more caustic than vinegar.

Why not just take it to a local radiator shop and have them clean it. They can also pressure test it for any leaks.
just my .02 worth....

john

I use CLR

The problem with acid cleaning anything is getting the acid on the surface. Any kind of grease, oil, etc. prevents this from happening. That's why the old time radiator flushes started with a caustic solution, removes all the petroleum products. As a substitute I'd try washing it out with a strong solution of Dawn dishwashing soap to get it squeaky clean and then hit it with some type of acid for the deposits. CLR sounds like a good choice.

The main issue is...that is not calcium.

It is solder bloom, caused by corrosion of dissimilar metals and is really difficult to remove.

Google "radiator solder bloom" for more info