Forwarding this from Burt Bouwkamp posted on another list: Regular vs premium gasoline will not effect engine heat rejection: i.e. engine cooling. At high speeds destructive preignition (due to using low octane gasoline and/or too much spark advance) could increase heat rejection but that condition would probably cause piston failure before you knew that you also had a cooling problem. By "destructive preignition" I am not talking about "spark knock" on acceleration - I am talking about the aluminum piston head getting so hot - and soft - that combustion gases blow a hole through the top of the piston. This happens when the fuel air/mixture in the combustion chamber explodes from self ignition rather than burning from spark ignition. Before we had all the electronic instruments that we have today (the 1950's) we use to set ignition timing just short of borderline knock on acceleration and we set carburetor mixtures 5% richer than borderline lean. You could tell borderline lean because the engine seemed to miss at road load. Actually, borderline lean provided the best economy but we went 5% richer than this because we knew the customer would not like an engine that didn't run smoothly. Burt Bouwkamp ------------------------------------ To send a message to this group, send an email to: Chrysler300@xxxxxxxxxxxxxxx For list server instructions, go to http://www.chrysler300club.com/yahoolist/inst.htm For archives go to http://www.forwardlook.net/300-archive/Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Chrysler300/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/Chrysler300/join (Yahoo! ID required) <*> To change settings via email: mailto:Chrysler300-digest@xxxxxxxxxxxxxxx mailto:Chrysler300-fullfeatured@xxxxxxxxxxxxxxx <*> To unsubscribe from this group, send an email to: Chrysler300-unsubscribe@xxxxxxxxxxxxxxx <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/