Radiator Cap

Thu Oct 16 17:38:10 GMT 1997

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So long as the horse is dead, there's no harm in beating it.

I agree wholeheartedly with the notion that cooling systems are optimized to run
at a specific operating temperature, and that the radiator will be less 
efficient at lower hot-side temperatures.

However your argument below brings up another question.  You state that

"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 ..."

Let's say that we put in a cooler thermostat, or remove the thermostat 
altogether, which as you note will lower the temperature of the water coming 
into the radiator.  Then, as you point out, the delta-T between radiator and air
will be lower than optimal, and the radiator will shed less thermal energy than 
otherwise.  Thus the radiator outlet temperature rises.  We agree to this point.

But, if the radiator outlet temp rises, the inlet temp will rise as well,  
bringing the radiator back toward its optimal coolant-air delta-T.  The T0 
cannot be raised to the point where the block delta-T is too low without the 
radiator inlet temp passing through the normal (optimal) operating temperature, 
which contradicts your argument.

mike skolones

______________________________ Reply Separator _________________________________
Subject: Re: Radiator Cap
Author:  diy_efi at coulomb.eng.ohio-state.edu at Internet
Date:    10/16/97 10:08 AM

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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Date: Thu, 16 Oct 1997 10:08:16 -0400
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