<VV> lower shrouds revisited

NicolCS at aol.com NicolCS at aol.com
Sat Oct 15 21:06:07 EDT 2005

I'm certain there are many examples where Corvairs have gone 100 k miles 
without thermostats or lower shrouds despite the poorer temperature control and 
longer warmup.

Here are the known benefits of removed lower shrouds: 
1) Lower head temperatures
2) Lower oil temperatures in very hot conditions.  
These facts are verified right in GM experimental test data and our 
collective experience over the decades.  

Here are the known benefits of installed lower shrouds and 'stats:
1) Faster warm-up (reduced engine wear, faster boil-off of condensed water in 
crankcase, reduced choke use leading to reduced oil dilution & reduced fuel 
2) More stable cylinder temperatures
3) Cylinder protection from water splash
4) Better heater operation
5) Better cold weather driveability (recirc plate open)

In the 60s and 70s, 100k was a normal engine life. Today, with fuel injection 
reducing the negative effects of cold enrichment (choke), and faster warm-ups 
and oil heating, smaller engines that warm more quickly , and taller gearing, 
150k to 200k is common.  Shrouds-on operation moves us in the direction of 
statistically longer engine life for the same reasons.

In hot environments, engine life is improved with the lower shrouds off, in 
cooler climates and/or milder operating modes, engine life is improved with 
shrouds ON.  For my climate here in Idaho, it's shroud & 'stats.  When I was 
towing a dune buggy (Corvair powered of course) behind my FC 140 camper, the 
shrouds were OFF.  

Many things can be easily surmised.  Sometimes correctly, sometimes not.
There's a lot of conventional wisdom out there - usually based at least
loosely on truth.  Sometime, however, the conventional wisdom outlives the

I wonder if this is one of those cases.  Is it possible that modern oils,
with their vastly improved anti-corrosion capabilities (as one example) have
made the speed of the warmup of less importance?

For some antecdotal evidence, which certainly proves little, my thermostats
died about 20 years (say 140K miles) ago.  At that point the doors stayed
open.  At some point I removed them.  I replaced my rings some years back,
probably about 40K ago, so the replaced rings probably had 100K on them.  I
have never had any blowby problems.

Experimental Conditions:
I drive hard.  My daily commute has varied from 15 miles to 8 miles to 14
miles each way, depending on my job/house location.  The car is seldom
driven if the temperature is below 40 degrees, since it is seldom that cold
here.  140, 4 spd, .040 over, step cut on heads with no cuts on pistons to
lower compression.  Oil changes - seldom, but 1qt added per 1000 miles (my
engine always leaks, no matter what I do).  Filter changes more often.  Dino
oil.  Air cleaner usage intermittant.  Not exactly textbook maintenance, but
no sign of oil related problems except for the oil soaked cardboard on the
garage floor. Roger

 It can easily be surmised that you are seeing engine failures caused by a 
lack of temperature control.  The upside is that it will give you a nicewinter 
project and enhance the welfare of our vendors. RonH

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