I checked the dipstick and I used about one half quart on the homebound leg of my drive to Death Valley. Still getting that "spark knock" sound occasionally. Purchased a new thermostat and will clean/flush out the radiator soon. I guess when you have a car of this vintage you should expect things to go wrong-wear out or just break! I love a challenge and this little car is going to be just that! OK, it is the next day and after a trip to the local auto parts store, I have new thermostat, some radiator cleaner and more 50/50 coolant. I get home, jack up on side of the car just so I can see underneath, and take a look at/for the draincock for the radiator. No luck in finding that but I did find the lower radiator hose. Of course there was no way I could get my hand up in that little space let along have the proper tool for the odd spring-loaded hose clamp holding in position! So I buttoned it back up,took back the cleaner and coolant and made an appointment with my local garage to do this chore for me. The days of being able to easily work on your own vehicle are long gone for most of us and that is a sad thing for us old shade-tree mechanic types. OK then, it's the next day AFTER visiting my local mechanic. He flushed the radiator and cleaned the coolant reservoir. The diagosis is once again scary.....there was oil in the coolant tank but none in either the crankcase or the radiator itself! This only opens up more questions as to where this oil came from. Film at eleven!