Losing coolant

[Don Bradner]

I've never had much coolant loss (except when dealing with replacing gate
valves), so I tend to check rather sporadically. A couple of days ago I checked
and it was not visible in the sight glass. Took roughly one gallon to bring it
back to the top of the glass.

This was approximately 480 miles since the last check (three separate runs with
several days between each).

I checked about 40 miles later (hot) and it was full. Checked it just now, cold,
and it was not visible. Took a bit over a quart to bring it to the top. This was
about 110 miles since the previous fill.

My oil usage appears about normal, 5 quarts on this trip over 4300 miles. I
would expect less if it was going into the oil (unless it boils off??)

I'm parked on clean concrete, and there are no signs of any fluids underneath
(It's been cool enough that the air conditioner has not been used, so not even
condensate).

Any thoughts on what to look at/for?

Don Bradner
90 PT40 "Blue Thunder"
Posting today by satellite from Hilton Head, South Carolina
My location: http://www.bbirdmaps.com/user2.cfm?user=1