Why is the coolant from my radiator disappearing?

(1998 Honda Prelude with a Jackson Racing supercharger) I replaced my old radiator because it cracked one day and was leaking. Before it had no problems as far as it just disappearing. I replaced my oem radiator for a Mishimoto radiator and ever since then it started disappearing.

Get your mechanic to do a pressure test on it. Chances are you got a blown head gasket, or even a small leak in the system. Check your oil cap and see if it's bubbly, whitish if it is then you got yourself a blown head gasket. A blown head gasket is really expensive to fix.

you can do a simple coolant system leak test with a cigar. Just blow the smoke from the radiator cap. It's worth a try maybe it's just a hose, and replacing a hose is pretty easy and cheap. But if you don't find anything that way. Just take it to your mechanic.

Water found around engine or on the floor, or evidence of water or coolant leak drying on engine = water leak somewhere
Water disappears with no other evidence = blown head gasket

Ain't no more to it

I reckon head gasket gone. Pressure in system prob blew the first rad. Only way its disapearing is either getting mixed wit the oil. A leak. R getting into combustion chambers. Do a pressure test on coolant system first and check for leaks. If no leaks probly head gasket then.

Huh! If your radiator is disappearing… Stands to reason that your reserve coolant will disappear with it. That said, did you check the petcock for slow leak? I found that to be a problem with a couple new radiators, especially those with plastic petcock drain. You would never realize, my friend…, except maybe with parking and idling, because the lost coolant goes blowin' in the wind, and with it, the answer to your question. (Sorry, Bob Dylan)

Pinhole leak somewhere in the cooling system. All the usual comments on finding a small leak. Right after starting, when it is still warming up, the system is developing pressure and the coolant is still below the boiling point. Watch the temp indicator, and when it comes off the low end of range, shut off the car and go hunting for water dripping out, probably very slowly, from somewhere on the radiator or the engine or a hose connection. It can be hard to find.
I had an old BMW M3 that was leaking coolant into the exhaust inside the head. It drove fine, but needed a coolant refill every couple of days. It took me awhile to figure it out. Antifreeze smell in the exhaust finally clued me in. K&N metallic block seal stopped the leak. It did not come back the rest of the time I owned it, like 5 more years. One thing about using leak-stop chemicals: they can clog up the radiator core or the heater core, so you have to be careful going that route. I instelled a wad of cotton gauze in the lower water neck of the radiator before I sent the block seal through the system. It was restricting flow, and the engine was hotter than usual while it ran to get the seal to set. After the cure time finished, I opened the lower hose and pulled out the gauze, and it had a fair amount of the block seal on it like hard melted plastic. Car ran fine after that, no change to it's normal temperature range.