I’ll recently purchased a 1995 E350 7.5 extended. It runs well and has proven that, but the temperature gauge is usually stuck at low for a while. It occasionally indicates normal, but today is has shown high (very high) all day. I know it’s not working properly, but I pulled over and checked to be safe. I heard a hissing from the left side of the engine block (close to the AC and what I believe to be the heater/blower). I don’t know anything about the van in terms of under the hood, is it really overheating? I started it with the radiator cap off, and fluid would gently rise to overflow. Fluid is plentiful and clean, and the radiator seems to be acting normally. From where it’s hissing, it seems to me like the blower is hissing rather than the cooling system. Does anyone have an idea of what could be happening?