Radiator Cap

[Clare Snyder]

Christopher G. Moog wrote:
> 
> B.E. Herron wrote:
> 
> > 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!
> >
> 
> Almost correct.  You can either leave the same water in contact for a period of
> time to absorb the heat (if the time is too long you will overheat) or YOU CAN
> MAINTAIN WATER IN CONTACT WITH THE ENGINE TO REMOVE THE HEAT.  It really doesn't
> matter if its the same water or a continuous flow (fast or slow).
> 
> > Tom wrote
> 
> > >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 !!
> >
> 
> Correct
> 
> B.E. Herron 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.
> 
> Bull, think of this way, if a fast flow of water is supplied the engine will
> away be in contact with cool water and the jacket side surface of the engine
> will be in constant contact (similar to soaking in) cool water.
> 
> Try the experiment turn on the hot water faucet and wait for the water to get
> real hot now turn the faucet on slow so its dripping quickly.  Place your right
> hand under the faucet and your left hand under your right hand.  You feel hot
> water with the right hand and not so hot water with the left.  Your right will
> absorb most of the available heat from the water before it gets to your left but
> the overall rate of heat transferred to your hand will be small.  OK now do the
> same except this time have the faucet running full speed.  You will now scald
> both hands and the water will still be hot.  You are absorbing more heat even
> though the water is not staying in contact with your hand very long.  If you
> still think the water can go too fast to absorb or give up heat try using a
> higher pressure water supply and let me know at what flow rate your hands don't
> burn (make sure your water heater is up to the task).
> 
> > 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).
> 
> While I'm not familiar with the NASCAR setups I do know you want to turn the
> pump as slow as possible so you waste the least amount of power.
> 
> Only possible problems I can see caused by operating without a thermostat are:
> 
> 1) overcooling
> 
> 2) Cavitation (even in pressurized systems some areas are near enough to the
> boil point to cavitate).
> 
> 3) Short circuited flow.  That is high flow through one section of the engine
> and proportionally lower flow through another.  Lets say with the restriction
> (thermostat or blanking plate) the front of the engine has twice the flow of the
> rear (some of the flow past the front cylinders is passed to the heads).
> Without the restriction the flow by the front may double but the flow through
> the rear of the jacket might only increase 20% (these are guessed on my part).
> If this were to happen you could have localized overheating.

This is exactly what I said several days ago - hot spots WILL develop in
certain areas of the engine without a thermostat or restrictor plate
installed. I'm not an engineer, but I have replaced numerous cyl heads
cracked by such abuse - particularly on Olds 350 and 455? V8s from the
mid seventies that had overheating problems(afterboil) pulling big
trailers - guys would pull the stats and crack the heads pronto. The
solution to the problem was simple - replace the stat with a "195 degree
F" stat and advance the timing about 4 degrees - then run nothing less
than premium gasoline. No more afterboil, even though the temp gauge ran
higher - and no more cracked heads. Wheather caused by coolant going
into a closed loop in the block and not hitting the rad, or flowing too
fast to shed the heat is a moot poit. The FACT of the matter is, running
without a thermostat or a rerasonable facsimile thereof can be dangerous
to your engine's health - and yours if that engine happens to be in an
airplane.
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