I just drained and filled my radiator for the first time since I've had the car. Before draining it, the coolant was about an inch below the filler neck, but looked OK. The overflow bottle was almost dry, with some very old looking cloudy green fluid. After draining, I filled the radiator to the neck with the engine running, and then added coolant to the overflow bottle until it was about half full. I also replaced the cap with a new 16 lb one. After driving home from the shop (about 7 miles), I didn't notice any coolant leak.

Today after another relatively short drive (maybe 2 miles each way with a 15 minute stop), I opened the hood to find a small stream of hot water squirting out of the radiator just below the cap. My first thought was "Oh crap, I broke something." My second thought was "Wait, maybe that leak was there all along. That would explain why the coolant was full up to where the leak is."

Did I break it, or did I just discover why the coolant was a little low?

If this is the original radiator, I'd probably shop for a new replacement. I took a radiator on a 40 year old Brand X truck to a radiator shop because it had a pinhole leak. They cleaned the corrosion, scale, and other crud out of it - only to have it spring a bunch of extra leaks because the crud was the only thing holding it together.

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"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

RockAuto has one for under $160 shipped. Is there anything else I should replace while I'm at it? Are there any tricks to replacing a radiator? It seems pretty simple: drain it, disconnect the hoses, undo a few bolts.

I thought stock radiator caps were 7 pounds, not 16.

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Casually looking for a Clifford hyperpak intake for cheap.

No, stock radiator caps stopped being 7 pounds well before the first slant-6 engine hit the road, and unless you are running waterless coolant, running a 7-pound cap is an unwise idea. Read (all the parts of) this.

As for replacement radiators: careful; quality is often not very good. You may find yourself wishing you'd spent more for a custom-built radiator.

If the only problem with this one is a pinhole leak, see if you're fortunate enough to still have a nearby radiator shop that's more than just a parts-swapping house; they can solder up the leak in a few minutes.

Also, the coolant level is not supposed to be right up to the filler neck ring unless you have a recovery system (more detail at linked article).

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

If it's a copper/brass radiator, and it's the filler neck, just torch it with a plumber's torch and solder......

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

The leak was about an inch below the filler neck, and you can see where something heavy fell on the neck, slightly buckling the radiator. I've already ordered the replacement, but I'll hold onto the old one just in case the new one doesn't work out.

I've successfully had 2 brass radiators repaired with a torch and solder. Held up for years.

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If it was easy, everybody would be doing it.