02 Nov 2003, 04:06, Roy J. Tellason (1:270/615), wrote to Charles Angelich:

Hi Roy.

 TW>> With the modern Plastic fans and tight shroud to maximise
 TW>> air flow through the radiator the hazzard is decreased some. 

 CA>> I think the 'maximize the air flow' is a cover up to avoid
 CA>> admitting any responsibility for those injured because there was
 CA>> none before. 'Air entrainment' would increase air flow if the
 CA>> shroud was not there.

 RJT> I've had any number of people tell me that they thought I oughta 
 RJT> get one in my truck,  even though they had no particular reason 
 RJT> to gain from my doing so...

Well, you did say earlier that it runs hot without the shroud!  The
"shrouding" began in the late 1950s to early 1960s as A/C was
becoming more common in cars, and cars began spending more time in heavy
traffic at slow speeds.  A round fan "near" the center of a
square radiator simply wasn't moving enough air THROUGH the radiator at low
vehicle speeds, and too many new cars were overheating.  This happened to
coincide with the beginning of EPA requirements, and manufacturers
"detuned" engines as a first step, which also resulted in higher
engine temperatures.  Along with the higher temperatures, they began
putting sealing strips at the rear of the hood, so the heat could no longer
escape over the winshield as it did in older cars.  Now the fan HAD to
build up enough pressure to force the naturally rising hot air back down
UNDER the car to escape.

This led to the further disastrous developments already discussed here. 
Instead of the one-piece stamped four-blade steel fans that had been used
for decades merely for 'circulation', the industry went to heavy five and
seven-bladed fabricated fans, ie: steel hubs with different material
flexible blades riveted or welded on.  At the same time, they changed to a
smaller sized fan/water pump pulley (or a larger size crankshaft pulley),
to speed up the fan.  This was good for city drivers, but at highway
speeds, the fan was using as much power as the rest of the vehicle, and was
extremely noisy.

Then came the fan clutch, some thermal controlled, and some RPM controlled.
 A good idea, BUT!  It ended up with too much spinning weight on the two
puny bearings built-into the water pump, and a LOT of premature water pump
failures, which if not recognized by the owner (seldom) often resulted in
the entire water pump shaft failure.  Instead of redesigning the water pump
with larger shaft and bearings, some manufacturers added a separate mount
for the fan, and divorced it from the water pump altogether.  This was
"nearly ideal" as they could now slow the water pump to reduce
cavitation wear on the impeller, reduce the load on the water pump
bearings, and at the same time increase the speed the fan even more to get
the needed airflow.

Of course, ALL of this could have been solved by installing a larger or
thicker radiator.  The last "big" car I owned had the hugh
shroud, a seven-bladed fan with stainless steel 'blades' riveted on, and a
thermal controlled fan clutch.  I noted that the radiator had three rows of
water tubes, but the tanks had positions for five rows of tubes, two of
which were never used.  If the radiator would have been built to use all
five rows of tubes, I probably could have gotten rid of the shroud, clutch,
and reverted to the simpler four or five-bladed fan at a slower speed.

 TW>> But for Some opening the hood is a Mistake. BUT that is what keps 
 TW>> mechanics feeding the family and placing a roof over theri 
 TW>> Heads!! :-)

 CA>> Auto mechanics lean towards the dishonest side of business to 
 CA>> manage to earn a living. The tempation to cheat seems too great 
 CA>> for many of them to resist. 

 RJT> I get *so* tired of that sort of stereotype,  which I think is 
 RJT> in large part perpetuated by those who don't understand 
 RJT> something and figure that because they don't understand it that 
 RJT> those who do are out to rip them off.  Goes back to the same 
 RJT> sort of stereotype about "tv repairmen" and no doubt those who 
 RJT> are technically savvy in terms of computers,  when it comes to 
 RJT> those who don't.  Not that there aren't some crooks out there,  
 RJT> but...

That stereotype now fits everywhere!  Look at Investment Banking, CPAs,
corporate ledgers, Accounting firms, Enron, Tyco, MCI, AOL, etc.  Crooks
are no longer limited to the 'technical trades'.


     Good luck...  M.

--- Msged/386 TE 06 (pre)