My radiator has a leak on the top how can I fix it without having to replace it just yet

Put some Bar Seal in it and don't worry where from. If you can't see where it is leaking, it may be leaking in the cylinder head. Is your oil okay?

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Stops and seals antifreeze/coolant leaks. Bar's Leaks Radiator Stop Leak Concentrate is specially designed to stop minor to moderate cooling system leaks and ...

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Aug. 15, 2019 - Bar's Leaks 1196 Radiator Stop Leak Seal the leaks in your radiator with this concentrated formula. It works to seal small leaks in your radiator or heater core. Bar's Leaks manufactures this product in the United States. One bottle can treat up to 4 gallons.

If its an aluminum radiator (which I suspect it is) not much you can do but replace it. You could try taking it out of the car and taking it to a local radiator shop. NEVER use that radiator stop-leak ****.

If your radiator is leaking,it's time to replace,all that stuff to fix leaks doesn't work,trust me,go to AUTOZONE,and get a new one,they come with a life time warranty,you will never have to buy another for that weekend.Always get lifetime replace parts.I will send a leak to your new radiator,need new cap and antifreeze.

You are leaking transmission fluid from either the fluid cooling lines that run from transmission to a separate reservoir in the radiator, or leaking from the reservoir itself. Hopefully, it's only the lines and may just need tightening to stop the leak.
There are two lines to the radiator's reservoir. One brings fluid from transmission to the reservoir, and a return line back into the transmission. Probably located on driver's side of the radiator, one will be near top of radiator, and one near the bottom. Small copper or steel lines that may also turn into rubber lines. Clean the area well with rags to locate the leak. Will probably need to have the car running to make it leak, while looking for it. You could also take a wrench and try tightening the fittings at the radiator, and tighten any rubber hose clamps that you see. If it's not the lines or hoses that are leaking, then the radiator may need to be pulled off for repairs or replacement. But 9 times out of ten, it is a leak from one of the lines.
When fixed, don't forget to check your transmission fluid level. Or keep adding till it is fixed.

You have a water leak from the sound of it or water is draining from over heating. Things to check for, leaks at the hose connections, leaks at heater connections on engine, leaks at water pump and any leaks at head gasket. Assuming there are no leaks check or replace or adjust your water pump belt. Take the thermostat out and run the engine without out it. If the problem is solved replace the thermostat recommended for you car. You can also have it checked as well.

Epoxy or other types of "quick fixes" will not work, or if they do won't fix the problem correctly. Even stop leak just plugs the hole from the inside, and plugs up the system. Best bet is to try and find the problem, which is usually a leaking hose, water pump, or radiator.
Once you find where the leak is coming from I can advise better on the best solution.

I’m happy to assist further over the phone at https://www.6ya.com/expert/jason_f0c65cd1b4d4ec9c

most coolant stop leaks will not work with anti-freeze at all,only clear water only. please read the label on the product and follow it to the letter.most stop leaks will not work under extreme conditions,such as a bad water pump or missing water pump belt,or bad thermostat. with common leaks along the radiator SEAMS they may help some. please seek a mechanic soon,you can damage your engine without proper coolant in it. which can lead to an engine replacement. where the steam is coming from is where your coolant leak is. it may only be a bad or faulty hose. a simple pressure tester rented from auto-zone or avanced automotive will reveal your leak.please follow the instructions with the rental equipment,and you will find the leak in the coolant system quickly. thank you for choosing fixya.com

There's a product called "Barr's Stop Leak" that provides a temporary fix...but when you have a radiator leak, its best to either get it fixed at a radiator shop or depending on model...get a replacement.
By just patching a leak...you are putting your engine at risk.

Remove radiator cap with engine cold, remove enough fluid so it can be replaced with stop leak. Add all stop leak & top off with anti freese. Put cap back on & start engine. Run engine for at least 20 minutes or take for a drive. Leak should stop if not too severe.Hope this advice helps if so rate accordingly. Good luck!

your radiator is probably bad small leak but itll do its deal of leak...