Just a couple of approximate values for reference: None of these relationships are very linear over wide ranges. Atmospheric pressure=14.69-0.43*(Elevation/1000) Sea level=14.69 psia, Pikes Peak=8.63 psia, Denver-about 12.1 psia Boiling Point of pure water=211.86-1.84*(Elevation/1000) Sea level=211.9 degrees F., Pikes Peak=186.1 degrees F, Denver-about 202.4 degrees F Dow shows these properties for ethylene glycol solutions and indicates a 64 degree increase in BP for 50-50 mix. There was no indication of any specific pressure cap. 30%: FP= +3F, BP=265F 40%: FP= -13F, BP=270F 50%: FP=-35F, BP=276F From an efficiency standpoint, the hotter an engine runs, the more efficient it can be. The tradeoff is efficiency vs. part life. Emissions come into play as higher temperatures can generate more NOX. Engineers develop efficiency curves for engines at various RPM and torque. It would be interesting to compare the charts for a 1955 C300 and a 2005 300C. Computer-controlled fuel injection and ignition reduce the compromises required for carbureted engines with ignition timing a function of RPM & vacuum. Sorry for the engineering rant. I hope it sheds some light. Rich Barber Ray Jones wrote: >Years ago, and maybe still now, the recipes on baking packages had >instructions for high elevations. This was because the pressure was loweer >above 5K feet, and it lowered the boiling point to the 190's, and changed >all the cooking characteristics. >As the operatation of modern engines changed, the need for higher temps >raised the cap pressures. The actual temp of today's engines is way higher >than the sealevel boiling point. > >But the most likely culprit is the guage/sender being inaccurate, and giving >a high reading. > >Hot (90's) in Arkansas, Ray > > ------------------------ Yahoo! Groups Sponsor --------------------~--> Yahoo! Autos. Everything you need to know about buying or selling a car. FREE Quotes, 360° Tours, Research, Blue Book, Compare Vehicles, Buy Used http://us.click.yahoo.com/kEZsdA/bwnGAA/YiGOAA/8LmulB/TM --------------------------------------------------------------------~-> 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 Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Chrysler300/ <*> 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/