krw wrote:
On Sat, 25 Jul 2015 12:19:18 -0500, Leon lcb11211@swbelldotnet
wrote:

On 7/25/2015 10:58 AM, John McCoy wrote:
Leon lcb11211@swbelldotnet wrote in
:

FWIW a small engine putting out extreme hp for its size does need lots
of cooling capacity. I remember when 2.3 liter produced 93 hp. It is
not unusual now to see less than 2 liter producing almost 300 hp.

The size of the engine is irrelevant, it's purely dependant on
the amount of power. Give or take a fraction, about 25% of the
chemical energy in the fuel comes out as mechanical energy (i.e.
horsepower), about 50% goes as heat in the exhaust, and about
25% goes as heat to the radiator.

That was my point, typically all engines are small these days but
produce up to triple HP so the need to cool is greater.
You left out natural heat radiation of the engine itself not counting
the exhaust. ;~) I'm an ex-GM service manager, actually my real jobs
were upper automotive management.
A few things that I could never quite understand and the factory reps
could not explain.

1. The heat extracted by the radiator is blown straight back on to the
source. How does that work? LOL

a. If air is going into the radiator and engine compartment, it
is also going out.

b. The air going through the radiator is still cooler than
the engine (so it is not adding heat to the engine).

2. I'm not sure how electric fuel pumps work to day but in the 70's and
80's many were submerged inside the fuel tank. I disassembled an
electric fuel pump and noticed that the fuel travels through the
electric motor including the brushes. How does the vehicle not blow up
when out of fuel but loaded with gas vapors?

No oxygen = no boom.


With respect to passenger cars, none of them have a radiator
big enough to handle their peak power output. The designers
depend on the fact that drivers rarely ask for full power for
more than a few seconds (passing on a two lane road, stop light
drag races, etc). Semi trucks, which do need to produce peak
power for extended periods, have vastly larger radiators even
tho their power output isn't much more (360-430hp would be
typical).

And hence the extra electric fans that often continue to run after
engine is turned off. I can assure you that engines reach peek
operating temperatures more often when sitting in traffic in summer heat
than when putting out peek power. If it were not for those fans every
vehicle would be over heating when is stop and go traffic.

They have electric fans because it's often cheaper than belt-driven
fans (think transverse engines). As far as running after the engine
is shut off, the engine block (hence water) will continue to heat
after it's shut down (as the pistons cool).

If it weren't for the fans, engines would overheat in any mode. I had
one overheat at when it was -20F and I was cruising at 70MPH, after
the belt broke.

I don,' believe so. The fan is there to move air through the radiator when
the vehicle is not moving fast enough help the radiator cast off heat.

You very likely had more going on to cause your engine to over heat,
especially at -20. 30 or do years ago we had a brutal winter, at least
for Houston. My service advisors were writing up an abnormally large
number of over heating vehicles. We had temps that never came above
freezing for days on end. And that was with fans working perfectly fine.
The simple problem was that those vehicles antifreeze was not up to the
task and the water/ antifreeze/ coolant mixture simply froze. There was no
water circulating at all to cool the engines. With -20 degrees and the
very likely fact that your fan belt also turned the water pump you probably
had no water circulation between the radiator and engine and or your water
froze. Unless you had a strong tail wind and the 70 mph vehicle wind
speed was effectively reduced to very little, you should have had enough
air passing through the radiator. Fans do not move air through the
radiator any where near 70. Mph. It as very likely that the water pomp
stopped turning fast enough to properly circulate the cooling system
antifreeze/ coolant.





Yamaha rates my bikes engine at 188hp (from 1 liter). It has
a radiator of 14" x 10". You wouldn't need a much larger
radiator for the typical small car.

Different set up altogether. The engine is more in the open and heat is
not captured by the engine compartment found on most 4 wheel vehicles.
And especially, the engine is not working nearly as hard as a similar HP
car engine lugging around 3000+ pounds and powering AC, which BTY also
contributes heat through the condenser, and vehicles that still have PS
pumps.

The efficiency of the engines should be similar so heat out ~
mechanical power out. Of course, moving 3000# takes ten times the
energy of 300# (at least on the first order) so will require 1ox the
cooling.

But yes in ideal conditions the vehicle is, in varying less degrees,
dependent on radiator capacity.