* Increased Load: Running the heater immediately after starting puts an extra load on the engine, especially when it's cold and still struggling to reach optimal operating temperature. The alternator has to work harder to power the heater blower motor, which draws significant current. This added load can slightly increase wear and tear on the engine and alternator.
* Slower Warm-up: The engine needs time to warm up properly. Demanding heat immediately diverts energy away from warming the engine oil and other components. This can prolong the period where the engine is operating with less efficient lubrication and potentially higher wear.
* Potentially Lower Battery Life (Indirect): The increased load could put extra strain on your battery, especially if it's already weak from the cold. This isn't a direct effect of the heater itself on the engine, but rather an indirect consequence.
However: The impact is generally minimal for modern cars. Engines and alternators are designed to handle this extra load, particularly for short periods. Unless you consistently run the heater on full blast immediately after starting in extremely cold temperatures for extended durations, the damage is unlikely to be significant.
In short: It's not ideal, but it's usually not a major problem. If you're concerned, wait a minute or two after starting the engine before turning on the heater to let the engine warm up slightly. This is especially important in extreme cold.
