Radiator Cap

Clare Snyder clsnyde at ibm.net
Thu Oct 16 14:10:43 GMT 1997


Tom Cloud wrote:
> 
> >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.
> 
> sorry, this is over-simplification -- and just not true !!  If you flow
> coolant across a surface -- and the coolant stays in contact with the
> surface -- the amount of heat removed is a function of delta-T  PERIOD !!
> Therefore, the faster the coolant flow (remember, it has to stay in contact)
> the higher the delta-T .... ergo, the more heat removed.  Where does this
> stuff about it having to stick around for a certain period of time come
> from?  The Wizard of Oz???  Certainly, the faster the coolant flows past,
> the less heat each unit of coolant absorbs -- i.e. the coolant won't get as
> hot -- but that's the point, isn't it??  ... to keep the "coolant" cool!
> 
> Now, in a closed system, where the coolant T0 (temp at entry to the
> heat source) is not constant but rather a function of a secondary heat
> exchanger (the radiator), another factor enters -- the variation in T0
> (the beginning coolant temp as it enters the block).
> 
> I think I buy the cavitation thing  ....  it allows me to keep my
> hard-headed reasoning  ;-)  .... the disclaimer I've been making all
> along is that the coolant ** HAS TO STAY IN CONTACT WITH THE HEAT
> SOURCE **.  So, with the demon, "cavitation", I can smugly allow
> those less informed than me am think that faster is worser -- cause
> it just could be.  Now, faster is not the same as "more" -- and we
> can all agree that "more" is better, can't we?  And by this, I mean
> more volume.  This may not be possible without extensive redesign
> of the cooling system -- if you want to keep the velocity the same.
> 
> Ah, well, now that I've shanghaied the diy-efi list for a couple of
> days, I think I'll go nurse my carpal tunnel wrists  ;-)
> 
> Seriously (er, cirrusly) guys, thanks for all the input.  I can
> honestly that I've not changed my mind one whit, but I have
> been enlightened  ;-)
> 
> Tom Cloud
> 
>      Madness takes its toll   .....   please have exact change
I'm not going to flog a dead horse forever, but you do not take your
reasoning far enough.
Delta T IS the key.
You have a finite supply of water, in a finite heat exchanger ( the
rad). The amount of heat removed by an infinite supply of water at a
fixed TO does not vary from that removed by a lesser supply until the
specific heat of the liquid is too low to absorb the required amount of
heat, at which point the coolant boils - removing more heat, but not
transferring it too well. So we agree so far.
Now go to the rad. With a fixed size, borderline at best, OEM radiator
running at design efficiency,a particular operating temp is required in
order for the delta T to be high enogh to efficiently remove the heat
from the coolant and yet supply water at a low enough TO to satisfy the
needs of the engine block. If the delta T is not high enough, the
marginal OEM Rad's efficiency drops, and not enough heat is shed by the
rad to remove the heat generated in the block so the TO is raised to the
poin the delta T in the block is too low, and not enough heat can be
absorbed without utilizing the latent heat of vaporization- which in
turn drastically reduces the heat transfer. Add to this the fact that
the coolant is now flowing too fast to shed all of it's heat through
this marginal-at-best heat exchanger, and you DO have a problem. One
problem feeds the next in a cascade effect, and suddenly you have a
severely overheated engine, with locallized hotspots causing head
cracks, burned valves, hard spots on cyl walls, heat checking,
detonation ( and it's associated damage), overboiling, you can likely
add to the list, instead of a mildly overheated one.

Now, if you have a huge, over-engineered, probably non-oem radiator with
excess capacity, you do NOT have a problem as your arguement now becomes
valid. 

You now have an overcooled engine, which at best is less efficient, and
at worst causes oil dilution and lubrication loss - which again causes
localized overheating (of bearings, etc.) and engine damage. The
thermostat was designed and installed for a purpose, and unless an
intelligent alternative, such as the Winston Cup restrictor plates and
speed-matched pulley sets are used, do yourself a favour, and use the
@#$* thing!!!!
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