Radiator Cap

[B.E. Herron]

-----Original Message-----
From: Tom Cloud <cloud at peaches.ph.utexas.edu>
To: bigbroncos at off-road.com <bigbroncos at off-road.com>
Cc: diy_efi at coulomb.eng.ohio-state.edu <diy_efi at coulomb.eng.ohio-state.edu>
Date: Monday, October 13, 1997 4:01 PM
Subject: Re: Radiator Cap



>> ....................................................... As for the
>>higher temp thermostats, I believe the reasoning is the higher opening
temp
>>makes the water stay in the engine longer in order to absorb more heat
from
>>the engine. Use too cool a thermostat and the water doesn't have enough
>>time to leech off enough heat, totally remove the thermostat and you risk
>>actually overheating, not necessarily boiling over but overheating the
>>engine. Water temp doesn't mean a damn thing, it's the block and head temp
>>that counts.
>
>now, here's where I have a problem -- probably showing just how cirrusly
>uninformed I really am !!  ..... I used to make water-cooled heatsinks.
>Doesn't mean I knew anything.  As long as the water contacts the
>metal, what difference could it possibly make how fast it moves.
>IMHO, this is the most ridiculous line of reasoning I've heard in a
>long time (no offense to you, Chris, ... I assume you're just repeating
>what you've heard or read -- seen it in some radiator ads myself).
>
>I mean, it's a law of physics that delta-T is required to remove
>heat .... and if you leave the water there, it warms up and then
>doesn't remove as much heat !!!

That's exactly correct.  You have to leave the water next to the metal for
_some_ period of time in order for it to soak up some of the heat.  Too long
and you over heat!

>
>I'd like to know .... not really losing sleep over this, but surely there's
>some guru summers that can ease my tortured mind ???  (I mean, I've
>run lots of engines with no thermostat -- always assumed the only problems
>were due to water not getting up into some high places that collect
>air pockets and the engine oil not getting hot quick enough to lube
>at first start.)
>
>What difference does the rate of flow have to do with heat transfer ??
>Like I said, seems to me that it's totally irrelevant as long as the
>liquid stays in contact with the metal -- in fact, seems t'me that the
>faster the better, since that keeps the delta-T at it's highest !!

Too fast and you don't take ANY heat from the metal and you over heat.  You
are correct, delta-T is required for cooling, but there is a finite time
period the liquid must be in contact with the metal for optimum
thermodynamic transfer of heat to take place.

Look at a Winston Cup car.  Those guys slow the pump down with the pulley
and then put restrictors in to fine-tune the cooling system based on the
track they're running (they change pulleys and restrictors for the different
tracks because of the different RPM and aero cooling, i.e. speed).

BEH

'73 Camaro RS
'66 Mustang Fastback