Radiator Cap
Michael Skolones
michaels at telerobot.com
Mon Oct 13 23:55:58 GMT 1997
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Newton tells us that the rate of heat flow from one region into
another is proportional to the difference in temperature between the
two regions (in this case, the block and the water). Therefore, given
an engine block of a certain temperature, cooler water will remove
more thermal energy per unit time than warmer water. A
lower-temperature thermostat will ensure a cooler supply of water to
remove the thermal energy from the block, and so cooler water is in
this sense more efficient.
Each volume-unit of water is in contact with the block for less time
if the water is flowing quickly, as compared to water that is flowing
slowly. Therefore each volume-unit of water carries away less thermal
energy if the water is moving quickly. But in a quickly-flowing
cooling system, more volume-units of water are flowing through the
cooling passages per unit time, so the amount of thermal energy
carried away per unit time will be the approximately the same
regardless of flow rate, the only difference being the change in the
rate of thermal exchange with temperature difference as described
above.
On the other hand, the question is somewhat irrelevant to automotive
cooling systems. To my knowledge a higher-temp thermostat flows at
least as much as a lower-temp thermostat for a given engine, once both
have reached the fully-open position. The only difference is the
temperature at which the valve fully opens, not in how much it opens.
mike skolones
______________________________ Reply Separator _________________________________
Subject: Re: Radiator Cap
Author: diy_efi at coulomb.eng.ohio-state.edu at Internet
Date: 10/13/97 4:57 PM
> ....................................................... As for the
>higher temp thermostats, I believe the reasoning is the higher opening temp
>makes the water stay in the engine longer in order to absorb more heat from
>the engine. Use too cool a thermostat and the water doesn't have enough
>time to leech off enough heat, totally remove the thermostat and you risk
>actually overheating, not necessarily boiling over but overheating the
>engine. Water temp doesn't mean a damn thing, it's the block and head temp
>that counts.
now, here's where I have a problem -- probably showing just how cirrusly
uninformed I really am !! ..... I used to make water-cooled heatsinks.
Doesn't mean I knew anything. As long as the water contacts the
metal, what difference could it possibly make how fast it moves.
IMHO, this is the most ridiculous line of reasoning I've heard in a
long time (no offense to you, Chris, ... I assume you're just repeating
what you've heard or read -- seen it in some radiator ads myself).
I mean, it's a law of physics that delta-T is required to remove
heat .... and if you leave the water there, it warms up and then
doesn't remove as much heat !!!
I'd like to know .... not really losing sleep over this, but surely there's
some guru summers that can ease my tortured mind ??? (I mean, I've
run lots of engines with no thermostat -- always assumed the only problems
were due to water not getting up into some high places that collect
air pockets and the engine oil not getting hot quick enough to lube
at first start.)
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 !!
At this point, I pronounce the ads by the rad makers "HOKUM". Now,
someone prove me the idiot that most have long suspected ;-)
Tom Cloud
Warning, dates in calendar are closer than they appear !
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To: bigbroncos at off-road.com
From: Tom Cloud <cloud at peaches.ph.utexas.edu>
Subject: Re: Radiator Cap
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