Radiator Cap

[Christopher G. Moog]

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.