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Stock 318 runs 30 degrees hotter with AC on- is this normal?

Fighting a hot running engine when the AC is on might seem like a loosing battle. But it's not. There are many things that contribute to over heating.

Making sure the cooling system is correct for an AC equipped car is first. Clean radiator, correct fan and clutch if equipped. Fan in correct position inside the shroud, usually about 1" in, and the correct diameter fan with the correct number of blades.

Ignition timing is critical. Even a stock engine running today's fuel needs to have much more base timing than factory spec. Something over 10° on a stock engine is a good place to start. But you must limit your total timing as well, no more than 34° total mechanical advance is another good place to start. Make sure your vacuum advance is working correctly. Another cause of excessive heat in the combustion chamber is a failed vacuum advance. Too much timing causes heat, and so does to little timing.

Fuel mixture needs to be correct. Lean mixtures make better power, but run hotter. The mixture must be within range to get good economy and make good power without creating excessive heat in the combustion chamber.

When all the above are correct, it is not unusual for the engine to reach temps over 200° in the heat of summer when idling in traffic and the AC on full blast. If the temp gets over 225°/ 230° I would start to worry, anything below that is livable. I believe the factory "HOT" light didnt come on till 240°. Stay under that and you would never know there was a problem if all you had was the idiot light to go by.
 
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