Question about radiator that leaks then stops leaking

[NotEnoughGPs]

2002 Grand Prix GT. 239,000 miles. Original radiator. Prestone green extended life coolant is what I use. Complete cooling system is flushed out about every 2 years which is around 50K miles. Now, I am getting a coolant leak about 2 tablespoons amount below the radiator on the passenger side, below the lower radiator hose. I can see the dampness of the coolant and drops of the coolant on the lower plastic protective guard. This does not leak all the time. It will only leak once every 2 weeks or so after driving maybe 1000 miles or so. I wipe up the coolant on the floor and wait the next day after driving to see if there is any more coolant, and there will be no leak. This has been going on since June. I do not want to add any kind of stop leak additive to the radiator. I have replaced both radiator hoses recently and checked the clamps and there is no coolant anywhere near them. I am sure there is no coolant leaking anywhere from the engine sides, so I know it is not the water pump or timing cover or coolant elbows. Has anyone ever had a radiator leak and then stop leaking? Anything else I should be looking a

[Scottydoggs]

yup i have, the plastic tank is cracked. let it idle and get hot, rev the engine up some and you'l see it leaking down the tank most likely.

or you can pressure test it. its a tool that goes on in place of the cap and you pump it up. this will force it to leak.

[SgtMarshal]

the last radiator I had to replace leaked like you describe, just in a different location. they end up not being able to hold pressure, when they need to hold about 16 psi.

[WarStryker13]

could also be the overflow hose, once it gets to 15 psi and the rad cap opens, the hose going to the overflow tank leaks.

Also explains why it's only after driving long distances, and not short, quick drives. it takes a while to build up that pressure.

[NotEnoughGPs]

I checked the coolant overflow bottle which is mounted to the passenger side strut tower. There is no leak in this tank.
Also, I checked the hose that connects the radiator (at tube next to the radiator cap) to the overflow tank. There is no leak in this hose even though there is 239,000 miles on it. This was a distinct possibility that it might be leaking because the coolant leak is below the radiator on the passenger side. That is where I found puddles of coolant on the floor. None on the engine side.
I never thought to have the radiator pressure tested. I will have this done next. Thanks everyone for tips

[Turbocharged400sbc]

Most often those tiny annoying leaks are from a week clamp between the aluminum core and the plastic end tank there is a rubber gasket crimp between them.
Since the aluminum expands and contracts more than the plastic the Rubber seal moves around and can leak a small bit.
I have also seen them leak coolant from around the trans cooler fittings for the trans cooler seals against the inside of the plastic tank and those large locking nuts hold it in place from the outside.
the most common failure is a crack in the plastic tank below the upper radiator hose connection.
It seems the plastic doesn't take temperature and pressure changes too well

[Turbocharged400sbc]

also I'd like to point out that most of the time I saw the small leaks... more than half of them were triggered because someone smashed the radiator support against a parking block to tweak it a ****hair.

[NotEnoughGPs]

Turbocharged400sbc, I can see that happening. I have been watching for more leaks, and have just not seen any lately. I ran this by my neighbor who is a 30 year GM mechanic and he said the same about leaks in the radiator core and plastic tank. I may have to install a new radiator. Thanks

[tom5170]

I had the very same exact leak but on the drivers side. Very slow leak for over 6 months until it got worse and eventually pissed out any coolant in it. I was lucky enough to have a radiator shop replace the radiator for $189. It ended up being where the plastic meets the aluminum on the radiator right where it's crimped together. You can try some alumaseal from auto zone for 3-4 bucks. I used that stuff on my old truck when the radiator had the same exact leak and it didn't leak for years afterwards. Just make sure you drive around a bit after you put it in. It's a powdered type sealer. Never heard of it causing any issues in cooling systems. A mechanic of 40 years suggested it to me.