Engine temp (was: all sorts of subjects)

[rdh@sli.com (Robert D. Houk)]

   Yes, and understand why the fan is even there........  Because at some point
   the open thermostat is not enough flow to keep the coolant from
   overheating.......  So the fan turns on to cool it down to the temp of the
   fan thermo, not the coolant thermostat level, which if it is higher, will
   negate the advantages of a lower thermostat......  Now, you have helped the
   cooling at "efficient speed" like on the open road, where there is enough air
   flow thru  the radiator to keep the coolant temp low....  But in town or slow
   traffic you really only open the thermostat sooner, but that doesn't mean you
   will necessarily be cooler, unless the fan runs too......  Remember, putting
   a cooler thermo and a cooler fan thermo in your car will make the fan operate
   more not less.....

For practical purposes, no, not really. You are still shedding the same
gross amount of heat, so overall the fan should run "the same" amount,
just sooner (lower temp). [Yeah yeah -- thermodynamics and all that; the
fan will run "less" at higher temps 'cuz the delta-T is greater and thus
more efficient heat flow, etc., and so forth. 'Twixt a 180F and 190F fan
switch, I seriously doubht you'd notice the difference with your wrist
watch driving around town!]

You can't put too cold of a fan switch in, cuz the engine just won't
accept more "cold" coolant than it wants, so the fan will pretty much
run "the same amount" whether you're running a 190, 180, or ???. (well,
yeah, a 32F fan switch won't shut off till November or so round these
parts, and maybe never in L.A....) You do want a "noticeably lower temp"
fan switch than your engine thermostat.

I have been running a "180" thermostat, with a "170" fan switch for about
the past 3 months.

Empirical observations:

 1)  the *HEAD* temperature runs 25F or so ***ABOVE*** your thermostat
     [195F "stock" thermostat runs the head at 220F; 180F thermostat
     runs the head around 205F (i.e., a "touch" above 200F index mark,
     which is 199 to 200F by my digital temperature probe stuck into
     the coolant flow, so the "temp guage" is fairly accurate...)]

 2)  the *HEAD* temperature readily "surges" 20F or so ***ABOVE*** where
     the thermostat more-or-less-kinda-sorta usually regulates the nominal
     head temperature. 

     In other words, with a "180" thermostat, the head pretty much runs
     at 205F or so, often "surging" to 220-230F or so (wide open throttle
     full boost 4000rpm etc. for 10-15 seconds), and eventually coming
     back down (half to two minutes later) as the "extra" heat eventually
     percolates its way down to the thermostat, which grudgingly admits
     a bit more coolant.

     *** Obligatory snipe at Audi ***

	Locating the thermostat in the block intake has got to be one of
	the stupidest most head-wedged-where-it's-damp-and-smelly design
	choices ever made!!!!! Whatever those assholes were on when they
	designed that system should definitely be outlawed! (and they
	should be taken out and *SHOT*! --and I'll even happily volunteer
        to help!

	I can accept that the German's design penchant for locating oil
	temp (etc.) guages below big-toe level is some strange cultural
	moral esthetic folderol (and thus not "wrong", just, um, German).
	But regulating the coolant temperature coming out of the radiator
	rather than coming out of the head (the *HOT* and *SENSITIVE*
	part of the engine) is just plain *WRONG*.

 3)  the *HEAD* temperature will heat-soak another 20F or so above #2
     when you shut the engine off. [With stock 195 thermostat, the head
     temperature quickly soars past the 250F point (pegging my 250F
     guage well past the 250F index mark); 180 thermostat keeps the
     needle to merely "past" -- but not pegged, usually -- the 250F in-
     dex after shutting the engine off after letting it idle for a long
     time to maximize it's latent temperature.

 4)  With all that incredible heat trapped in the engine, you'd think
     the passenger compartment heater would fry eggs . . . but no . . .
     (it is better than my old Lotus Europa though, which could just
     about keep up with 40F weather; the UrQ is good to the teens...)

Any engine cooling system which regularly permits the head/coolant tem-
perature to *exceed* 250F is really, er, ah, bad.

I *HIGHLY* recommend everyone replacing their stock 195 thermostats
with 180 thermostats (and 170 fan switches too). If I could find a 170
thermostat, I'd probably go for that too.

					-RDH