My suspicion for this scenario (below) is that the fan clutch is not working and/or the fan shroud is missing. I'm thinking that lots of air over the radiator at highway speeds will keep everything cool. Once you slow down and get into traffic the fan clutch should take over and engage the fan to keep plenty of air going through the radiator. If it's not working I think what Kle has described would be the end result. Eventually the slow moving fan will pull enough air through the radiator to finally overtake the temperature increase. I would suspect that running the AC while in traffic causes temperature increases as well. A sure sign of a failed fan clutch. Sjak pointed out earlier an item that I missed regarding timing. Retarded timing will always tend to make the engine run warmer. Early smog control systems here in California used to block off the vacuum advance until the engine reached operating temperature in an attempt to warm the engine faster. I've seen where members have retarded timing a few degrees to avoid a pinging problem. Another culprit I just thought of is fuel/air mixture. Sometimes people will lean out the fuel mixture in an attempt to get better fuel economy. This only makes the engine runner hotter. Ok, it's time to click on the "send" button and go to bed. Ken 67 Crown 4 Dr Ht 68 LeBaron 4 Dr Ht I then get off the highway (and probably turn off the A/C temporarily). I have to slow down, or enter stop-and-go traffic, so the engine temp starts to climb. It will eventually cool down, as the cooling system catches up with the big heat dump from the lower airflow (presuming it isn't overwhelmed and overheats), but right now it's climbing. ----------------- http://www.imperialclub.com ----------------- This message was sent to you by the Imperial Mailing List. Please reply to mailing-list@xxxxxxxxxxxxxxxx and your response will be shared with everyone. Private messages (and attachments) for the Administrators should be sent to iml.webmonster@xxxxxxxxx To UN-SUBSCRIBE, go to http://imperialclub.com/unsubscribe.htm