Hi, 1992 RM wagon, 78,000 miles, no leak but hear a hissing and losing coolant, slowly.
My car doesn't leak anything. In great shape. I noticed the temp gauge
going up while sitting in a parking lot. I turned it off before it overheated.
Added cooling and seemed fine for a while. Replaced radiator cap and that
seems to do it. Now, reservoir level low, added water and after a drive 20
miles, nothing dripping that I can see or that is on the ground, but hear
hissing nosie. what can it be?