[wolf k]

As a mechanical engineer who has worked with large marine diesels engines all my adult life, a spread of 80 degrees F. at the exhaust is not out of the ordinary.
Couple of points:1) To get true accurate exhaust temp readings, you need thermocouples installed directly in the header pipes. An infrared gun is helpful in troubleshooting, but not for absolute numbers. Your readings can be affected by the thickness of the coating, positioning of your gun, and airflow from cooling fans across the primary pipes.
2) In large diesels, exhaust temps are monitored only when the engine is under a moderate load to full load. At idle, and low loads the exhaust temps are usually way out of balance and the alarms are automatically inhibited. When you measured your temps, your engine was not under load at the time, exhaust temps fall rapidly when unloading an engine.
3) It is combustion pressure that we try to balance in diesel engines, sometimes exhaust temp and combustion pressure do not coincide due to several factors. Exhaust temps can be a tell-tale to combustion pressure but it is not an absolute to tuning an engine. Manufacturers give acceptable exhaust spreads.

So, if this information crosses over to gasoline engines, which I believe it would, I would not be alarmed at your readings, A/F measuring would probably be more helpful, or just reading your plugs at this time. Hope this helps, Wolfgang