Are you really, really sure that the sound is from air coming out, not
going in?

Once, a few years ago, someone on this list said that he had a coolant
pressure gauge on his dash.. I have wanted one ever since, but have not run
across a suitable gauge that would read a reasonable amount of both
pressure and vacuum.  I would also need to find or make a suitable fitting
to attach to the top of the radiator (banjo bolt?).  Maybe some day...

Larry A.

On Fri, Jan 1, 2016 at 12:57 PM, Jim Felder <jim.felder@gmail.com> wrote:

> 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
>