My Nova overheats with the A/C running
I am hoping you or another reader can help me with an overheating problem in my Nova equipped with the L48 350. I factory ordered this car in 1972 while stationed in Germany and had it waiting for me in Denver, Colorado, when I came home from my first tour there, so it is a one-owner car. I never had any cooling problems in the past even while using the air conditioner in Kansas during the summers while stationed there.
In 1988 the cam timing gear broke at 145,000 miles and a couple of pistons were also damaged so I had Bud’s Machine Shop bore it .040 over, put in new pistons, bearings, cam, oil pump, and valves. It ran great, but due to life’s complications it stayed in the garage, not even being run some years, until 2013.
I then discovered it would get hot if the air conditioner was on and the fan was on full speed and I was on the Interstate at above 60 mph. If the air conditioner was off, it wouldn’t get hot enough to be concerned. Furthermore, if the fan isn’t on or is on low speed, it doesn’t get as hot.
In trying to solve the problem, I first had the AC checked and was told it was OK; then I flushed the cooling system and changed the thermostat. And since it was drained I had the radiator tested, and replaced both hoses with no change. My next attempt was to change out the fan clutch. This also didn’t help, so I replaced the water pump and still no solution.
I then discovered that at some point in the past I had installed a 30-amp alternator and it calls for a 60 amp, so I put the correct one on and still the problem was not solved. Even though it was a shot in the dark I replaced the factory triple-core radiator with a four-core. The problem still exists, but it does take longer to get real hot—30-240 degrees—according to the tester. The ignition timing is 10 degrees at 900 rpm and 38 at 3000 rpm. I am at a complete loss as to what the problem is.
From your description it sounds like the car didn’t come with air conditioning and that it was added at the dealership or possibly later. The reason I say that is you mentioned the 30-amp alternator, which would be fine for a car with no air conditioning, but inadequate with air conditioning added. Cars with air conditioning need a more effective fan, too. In the 1950s, Chevrolets with air came with a special five-bladed fan, and with a fourbladed production fan or an after-market fan they overheated.
I would investigate which fan was used with air conditioning on your car originally and install one of those if the one you have now is not correct. However, if what you have is the correct fan, I would consider going to a bigger, better heavy-duty fan and maybe even an auxiliary pusher on the front of the radiator as well. You can have it thermostatically controlled by a probe in the radiator, or simply install a switch under the dash to turn it on when you turn on the air. But be sure to turn it on before the engine starts to heat up.