Date:         Wed, 29 May 1996 10:05:49 -0700
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         jwakefield@4dmg.net (john wakefield)
Subject:      Re: More 83.5 cooling

Dave Sidote wrote:
 "This is the strange thing. If I stop at a light and the temp goes up when I resume 
driving in third gear the temp gauge needle goes toward the left of the light (meaning 
the needle is still within the circle of the led, like it is running cooler) BUT if I
drive in 4th gear (highway speeds) the gauge only drops alittle from the right. 
Shouldn't it be the other way around. If the van is going 55mph at the same rpm (?) 
shouldn't it be cooler than going 35mph in third gear?"

  Assume identical engine speeds in third and fourth gears, and accept your estimate 
that your gear staging is .636 down from fourth to third, and that at this RPM your van 
goes 35 mph in third or 55 in fourth.  You still have very different heat loads imposed 
by the work required to propel your van at these two speeds and the air flow through 
the radiator is different.  You seem to assume the increase in heat exchange 
through your radiator with increasing air speed (not linear, but for this discussion 
close enough for explanation) will be less than the heat load increase generated by 
your engine (also not linear but includes some squared functions).  The roughly linear 
function is going up slower than the log function, so it gets warmer until the first 
stage of the cooling fan comes on to assist air flow.

  John