With the right amount of coolant in the radiator, it won't necessarily always be all the way to the top.
If you don't have antifreeze, throw in a gallon of it. It'll make a leak easier to see. Check hoses and radiator for leaks. Check around the area where the hoses that go to heater core through firewall. Sometimes it's better to check for leaks after you've driven around for a while and the car is hot. Put in park while still running and check around for coolant leaking. (that's really about all you can do)
(Get a 180 thermo).
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351W-powered 1979 Ford Mustang notchback
Stock 5.8L under 4" cowl, C4 w/ shift kit
Holley 750 cfm, Edelbrock Performer RPM intake
1 5/8" MAC shorty headers, Al driveshaft
2.5" Off road H-pipe, 2-chamber Flowmasters
Front: 225/60/15, Rear: 255/60/15 Eagle GT II
Weld wheels (15x6;15x8), 8.8" Rear w/ 3.55s
14 x 4” K&N air filter (getting the Xtreme setup someday)
"Red, thou art my companion. Hasten now your quickened metamorphosis to Green that I may conquer all who dare abide there beside me. May they be left thither behind burnt black." ---Fox Body