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Re: Thermostat/Oil Cooler (long... but maybe useful...)


Hey Jesse-

> I just read an article on this question in the Gene Berg catalog. He
> states that there is an decrease in engine life between 13 to 19% by
> removing the cooling flaps.

Knowing the type of "testing" Gene Berg typically used, I can just about
guarantee that those numbers hold no significance.  They were probably just
pulled out of someone's..........


> When the motor is receiving its full
> cooling potential during warm up the motor cannot heat up at the same
> rate from the case to the cylinder heads, causing cracked heads,
> misadjusted valves and cylinders and pistons heating up unevenly
> causing ring and cylinder wear.

The only one of these that makes sense is ring and cylinder wear.  Think
about it. (or read below)


> He also states that the longer the
> engine runs cool the more wear and tear there is on the bearings.

True.  But, then again, the bellows thermostat on the VW doesn't do much to
help this.  Staying away from thick, straightweight oils, having working
pressure-relief valves, and running at a conservative RPM until warm does.


> Also the air control flaps act as air directors forcing the air
> across the oil cooler at just the right direction so the air flows
> over it and on to the cylinders at maximum efficient.

That's just *slightly* inaccurate :-)

Here's the thing: there are six different kinds of cooling systems used on
aircooled VW engines (excluding any really archaic 25-36hp stuff... I dunno
specifics about these).  All of regulate based on the air temperature under
the 1 and 2 cylinders.  The T1 and T3 are fully open at 65-70C and the T4 at
80-85C (or is it 85-90C? I don't remember offhand).

The first is the older T1 style - a big baffle is placed in front of the fan
shroud opening.  The Porsche 356 copied this.  In effect, this regulates the
amount of cooling air given to both the oil cooler and the heads/cylinders.
However, this is somewhat clunky, is somewhat prone to failure, and is
somewhat expensive.

The second is the newer non-doghouse T1 style - the infamous flaps.  Flaps
are placed atop the heads/cylinders that only regulate the air to the
heads/cylinders!  However, with *most* of the air outlet blocked, it *kinda*
keeps the oil cooler from getting cooled off much.  This system is a bit
more robust and cheap, but that's not the main reason VW changed.  They
changed because of the simultaneous change to fresh air heaters - if they
regulate overall air intake, the heater air is also regulated.  Was this
done for preferentially cooling the heads over the cylinders?  No.  That was
NOT on the VW engineer's design board at the time.  And, the more I think
about them and stare at them, the less I believe that they do actually
prefer the heads over the cylinders during warm-up, although I do agree that
a setup that actually did this would be somewhat useful (see below...).

The third is the newer doghouse T1 style.  The change from the previous one
is that the oil cooler receives full-blast air all of the time - it is NOT
regulated.  Only the heads/cylinders are regulated.

The fourth is the newest doghouse T1/911 style, currently used on the VW in
Mexico today and on the 911 for it's entire life from 1964 on.  The change
from the previous one is that there is NO cooling air regulation:
full-blast to everywhere all of the time.

The fifth one is the T3 style.  There are a pair of flaps that regulate the
air going to both the oil cooler and heads/cylinders - hotter = more.
Functionally, this is most similar to the earliest T1/356 style air control.

The sixth one is the T4 style. This one is very unique.  It looks kinda like
a T3 setup, but has one very important difference!  When fully closed, the
system blocks all cooling air.  When partially open, the system lets air to
both the oil cooler and the heads/cylinders.  As they open more and more,
the system begins to block cooling air to the oil cooler!  When fully open,
the oil cooler is COMPLETELY blocked!  All cooling air is directed toward
the heads/cylinders.  Clearly, if left in stock form, simply removing the
thermostat and leaving the flaps in place will kill the engine.

So, what's to realize from all of this?  First of all, VW never cared one
bit about regulating air to the oil cooler.  Any and all regulation of
cooling air to the oil cooler is purely coincidental.  In fact, the oil
cooler itself was originally an afterthought and it's only purpose is to
keep the oil cool, NOT the engine cool.  I know that this is exactly
contrary to what most people believe, namely that VW intended oil to be a
coolant, but oh well.  That's the truth.  Looking at what they did over the
years, especially with the T4, it can clearly be seen that oil was NOT
intended to be a coolant - just a lubricant.  And, if oil gets too hot, then
it gets too thin, so they put in a cooler ONLY to keep the oil cool and
thick enough!  That's it!  In fact, the oil cooler was considered so
unimportant to overall engine cooling that it was shut off on the T4 when
the thermostat signaled that the engine was running hot.  (BTW, this is why
I laugh when I ask people what they did to the cooling system to offset
their kewl 4- or 6-fin hi-po T1 heads and they answer with a big oil cooler
:-)  Now, there IS a psuedo-thermostat on the oil flow itself into the
cooler - the pressure relief valve.  When cold, less oil passes through the
cooler than when hot.

The ONLY function of the cooling air control system is to limit air to the
heads and cylinders (non-preferentially) when the exiting air temperature is
low.  There is one additional function on the T4 - block cooling air to the
oil cooler and send even more to the cylinders and heads when very hot.
And, this makes sense - the clearance between the pistons and cylinders is
larger when cold than hot.  [BTW, this is one downfall of forged (Aluminum
2618... or is it 2816?  I don't remember...) pistons as opposed to the new,
cast hypereutectic (Aluminum 390) pistons - the new ones run with a
considerably smaller clearance due to lower thermal expansion.]  So, when
colder, the rings and pistons wear more.

And, the additional function of the T4 makes sense - if the heads get too
hot, the heads will crack!  This is contrary to what you said that Berg
preached - heats crack when they are too HOT, NOT when too COLD!

But, how important is the control of warmup to the cylinders and heads?  To
cars driven in non-arctic climates, it doesn't matter much at all.  In fact,
Porsche disregarded it with the 911 and VW with the newer aircooled Beetles.
The argument of dissimilar cylinder materials can't be used either: all
aircooled 911 engines (cyls of solid cast iron like VW, cast iron sleeves
and aluminum fins, and solid aluminum) used the same sort of cooling
arrangement.  If you've ever used a cylinder head temperature gauge, then
you know how quickly the heads heat up even without thermostatic control on
a 30F day even when driving conservatively to make the cold oil happy
(sorry, I haven't done it in the snow and so don't know about much colder
:-).


> what i have learned is that vw engineers were a lot smarted than me
> and most anything that i do to the engine that was not stock is going
> to sacrifice longevity and quality. Vw did not just slap things
> together and hope for the best. They spend years researching and
> developing little things like how to build an efficient cooling
> system.

Unfortunately, that is not quite true :-).  Designing a system that actually
did limit cooling air to the cylinders and not heads during warmup based on
actual cylinder (not head or air) temperature would be nice, but expensive.
So, VW nor Porsche ever felt it was worth the expense for the gain.  Also,
adding an oil filter like every other auto manufacturer is a big plus.  VW
engineers weren't the best - they did only what was needed and for as
cheaply as needed, especially when discussing the T1-based engines (T4 got a
little more money thrown at it).  I mean, c'mon, why did they continue to
use the magnesium-alloy case even when they knew that they didn't last?  Sim
ple - getting magnesium from sea water was dirt cheap!

Take care,
Shad

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