I have a mysterious coolant leak that show up when tempertures drop to the mid 50's. Once tempertures are back up to 60's it does not leak. It happens overnight when tempertures drop. A table sppon or so leaks out some where around the timing cover.

I'm thinking there may be a crack in the timing cover somewhere and the crack opens some when cold and closes tight when hot. There are no leaks while driving it and during the spring and summer months. I have not had to add any fluid during the summer.

Strange. Any one have something like this before.

Where exactly do you see the coolant puddle? What is your water-coolant concentration?

It seeps out right close to the lower radiator hose. It seems to be a little wet behind the timing cover above the hose outlet. Seems to drip down on to the hose and eventual make it on to the floor.

I've been using 50-50 mix.

Expansion/contraction possibly. Try tightening timing cover bolts that go thru water pump hosing into block. Rad stop leak may cure it as well.

I would really inspect the water pump weep hole and/or seal, I don't think a crack would quit with temp change.

I second the weep hole on the water pump. Grab a mirror and look for a little stain coming out of it.

I have tried tightening all the screws and nuts last winter. Never could get it to stop. So you think the weep hole could let some fluid out when when expanding \ contrating. I'm using the flow kooler water pump.

Just funning how as soon as weather warms up, no more leaks. I though maybe a hairline crack in the timing cover may cause it.

I am planning a radiator change soon so maybe I can get a better view.

This stuff has worked for me before...
http://barsleaks.com/product/radiator-stop-leak-concentrate/

https://www.flowkoolerwaterpumps.com/info/common_waterpump_failures.html

I would think hose connection or weep hole, My Final Answer.

I would never put stop leak in a classic car. That's designed for your POS daily driver you're trying to keep going without spending any money

Get an inspection mirror and look at the weep hole, the mating surface of the pump to the timing cover and anywhere else you can stick it to see evidence of leakage.

The aluminum timing covers and cast water pumps can cause the leak at the gasket especially if the timing cover mating surface is not EXACTLY true. Tightening things up won't fix it.

Consider getting a pressure tester. Pump it up to 16 psi cold and you should be able to find the leak. Leaks can be tricky to find since they often only leak under pressure when the motor is hot and it evaporates.

It does not leak running. Only setting and when air temps are below 60. Maybe i can put pressure on it when the weather turns cold.

My point is that it may be leaking when running and you just can't tell because it evaporates. That's where the pressure tester comes in.

Yes I understand. Every time I can smell antifreeze when evaporating like that and you loose fluid and have to add it. I don't smell it or loose fluid so it can not be doing it doing the warm months. Only time I loose fluid is when temperature drop and it is parked overnight. All summer I drive it, no fluid lost I do not have to add any coolant. It sets in may garage for a couple weeks with out moving. I check for leaks and none. Then it turns cold, overnight, I get out and look and I loose a couple tablespoons on the floor.