Radiator Cap

[John Hess]

I'll try that one...

How about, when you remove the thermostat, the pressure of the system
decreases, the boiling temperature decreases, the coolant boils at a
lower temperature (both in the cooling system and in the overflow -
where available- catch tank), the mass of the water in the cooling
system decreases, decreasing the pressure further, causing further loss
of coolant.  The result...overheating!


> ----------
> From: 	Johnny[SMTP:johnny at johnny-enterprises.com]
> Sent: 	Thursday, October 16, 1997 4:24 AM
> To: 	diy_efi at coulomb.eng.ohio-state.edu
> Subject: 	Re: Radiator Cap
> 
> Sounds good, but it doesn't really explain why the engine totally
> overheats when you remove the thermostat and then drive down the
> freeway.
> 
> -j- (try again)
> 
> 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.
>