IN MY OPINION: IF YOU DONT NEED HEAT, BLOCK EM!! I REMEMBER JAMES TAYLOR IN THE MOVIE "TWO LANE BLACK TOP", WHEN HE WAS DRIVING CROSS-COUNTRY, WINNING MONEY DRAG RACING IN HIS 55 CHEVY, 454 WITH HAND BELT HEADERS AND SLIDING PLASTIC WINDOWS; AND WAS ASKED ONE COLD NIGHT BY A PASSENGER "WHY DID YOU DISCONNECT THE HEATER??" HIS REPLY: "IT SLOWS IT DOWN!" I ALSO REMEMBER WHEN I DID THE CROSS COUNTRY DRIVING IN THAT 390 GTA FAST BACK, IN THE SUMMER OF '72 AND I WAS ON THE EDGE OF BOILING OVER, I WOULD TURN THE HEATER AND BLOWER ON FULL BLAST!!YES IT WAS NEAR 100 DEGREES OUT SIDE! BUT IT DID THE TRICK, USING THE HEATER AS A LITTLE ADDED RADIATER LOWERED THE ENGINE TEMP, PROBABLY 30 DEGREES! ALL THE BEST, MARLIN.