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Mysterious coolant leak

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After rolling my car out of storage a couple of weeks ago, I discovered some coolant on the ground where the car had been parked. It was a small amount, probably 1 to 2 tablespoons and located somewhere up front between the radiator and the front fire wall. I pulled the spare tire out and had a look from the top side and could not find any wet spots or spots with dried residue indicating a leak. Bringing the car up to temperature and letting it idle did not generate any dripping. I drove the car home without issue and I have been driving regularly since. I was hoping that a new wet spot would appear giving me a clue as to where I should look; however, the car has remained dry since coming out of storage.

Since nothing is visible from the top, I expect that I am going to have to get the car up on jack stands and have a look underneath to see if I can spot the source of the leak. Does anybody have any suggestions for obvious candidates for an intermittent leak source? If nothing reveals itself via inspection I may have to get an adapter cap for the coolant tank and apply some air pressure to see if I can induce a leak.
 
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it could be the lower plastic pet cock , my car will do that based on how cold it gets in my garage and how long cars sits idle . once i start using it again no problem .
 
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it could be the lower plastic pet cock , my car will do that based on how cold it gets in my garage and how long cars sits idle . once i start using it again no problem .

Well you win the cigar!

It wasn't my lower rad petcock; but, the upper rad petcock. The tell was a tiny little puddle of coolant that had collected on top of the fan shroud just below the upper petcock. The puddle was probably a teaspoon. More may have oozed out but this was what was trapped by the little dip in the fan shroud where it had collected. If you looked really close at the shroud you could see faint trail of dried coolant from the petcock down along the shroud. When I first checked after pulling the car out of storage there was nothing obvious there, perhaps because it had evaporated.

The temperatures here have been really variable. I wonder if the temperature drops are responsible for inducing the leak because of contraction of the rubber O ring. I will plan for replacement of the rubber O rings on both the top and bottom petcocks.
 
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Well you win the cigar!

It wasn't my lower rad petcock; but, the upper rad petcock. The tell was a tiny little puddle of coolant that had collected on top of the fan shroud just below the upper petcock. The puddle was probably a teaspoon. More may have oozed out but this was what was trapped by the little dip in the fan shroud where it had collected. If you looked really close at the shroud you could see faint trail of dried coolant from the petcock down along the shroud. When I first checked after pulling the car out of storage there was nothing obvious there, perhaps because it had evaporated.

The temperatures here have been really variable. I wonder if the temperature drops are responsible for inducing the leak because of contraction of the rubber O ring. I will plan for replacement of the rubber O rings on both the top and bottom petcocks.

I wouldn't worry unless they continue to leak , just remember do not overtighten petcock , snug is fine
 
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mine was the lower one... mine is always garage in SOCAL. So, probably just age related rather than temp.

I replaced both the plug and O ring..

The temperatures here have been really variable. I wonder if the temperature drops are responsible for inducing the leak because of contraction of the rubber O ring. I will plan for replacement of the rubber O rings on both the top and bottom petcocks.
 
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It wasn't my lower rad petcock; but, the upper rad petcock. The tell was a tiny little puddle of coolant that had collected on top of the fan shroud just below the upper petcock. The puddle was probably a teaspoon. More may have oozed out but this was what was trapped by the little dip in the fan shroud where it had collected. If you looked really close at the shroud you could see faint trail of dried coolant from the petcock down along the shroud. When I first checked after pulling the car out of storage there was nothing obvious there, perhaps because it had evaporated.
This is what I was going to say as this is exactly what happened to me this past winter. Radiator upper petcock O-ring. It just started leaking out of the blue in the middle of the winter, collecting on the fan shroud but eventually trickling on to the ground. It also left a tiny residue on the lower aspect of the rad. So slow that I put some paper towel on it & it absorbed the coolant for 2 months. Not much temperature change in my garage. When I removed the o-ring to change it, it had some obvious flattening, so I could see why it was no longer sealing. Replaced and no more leaks.
 
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