Not very important as my car is running and cooling well, but I am curious
about this issue which I can't come up with an explanation for.

I recently installed new radiator hoses and with the help of this list,
finally got it right by going to a 1.9 waterboxer reservoir on my 1983
diesel.

Everything is good and seemingly snug, but on a cold night like last night
and a few before, I find a small puddle, what I always called a "cold leak"
that doesn't appear when the engine is running or when the weather is
warmer. It's so slight, I can't really tell exactly where it's coming from,
maybe a couple of tablespoons when it gets down around freezing.

When I open the pressure cap, I get a burp of air. This is from cold, no
starting or running whatsoever.

How can this be? There's obviously a small leak somewhere around the
reservoir, maybe even the cap or a connection or even the coolant level
indicator. There just isn't more than a few drops on the hoses to leave a
trace. I may powder it with flour dust to find out more about where it is
coming from and how it gets to the ground.

But back to the burp: air in the system and coolant in the system is at
equilibrium with the atmosphere when it is added, right? Then you drive the
car, and it heats up, then the system becomes pressurized which raises the
boiling point of the coolant even further. Then the car sits out overnight,
and the temperatures the next morning are even lower, so you would expect
no pressure or, as the system is designed to take advantage of, a vacuum to
suck in coolant from the overflow tank to displace the air, right?

This isn't happening. I suspect it's a crappy blue cap, the second I've
bought in two months, is preventing the intake of coolant. But maybe it's
because of this residual pressure that I can't figure out. why is  there a
burp when I open the cap in the morning instead of nothing?

Anyone?

Jim

Jim