ok i give up. ive replaced the radiator, thermostat, checked all hoses, replaced all filters, normal tune up junk, and i cant get this heat issue under control. it runs fine for a while but the gauge goes up a lil bit and i lose all heat and then returns back to normal. traveling at different speeds changes nothing. i have never seen any sign of a leak but have to refill the antifreeze often. im thinkin maybe an airbubble or bad heater core but also havent seen any visible signs of it goin bad. (wet floor on passenger side, antifreeze on windshield,....) nothing. im ready to pull the motor and start over lol. hopefully someone can help.