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

Hey Jim- 

> You may well be, but I remain skeptical. I've looked over the books 
> that I have and I can easily see all the main features you describe. 
> I just can't tell exactly how all these parts fit together when warm. I 
> wish I had one to take apart right now, but I don't. I've replaced my 
> share of type 4 thermostats and cables, so I am familiar with all 
> that stuff, but the mystery is what happens just above the oil 
> cooler. Yes, I know where it is.  ;-) 

Yur gunna hafta trust me on this one, no matter how poor my grammar is :-).  
I'll be back in IL in late September.  If you like, sometime you can come down 
to our VW playground in Momence (between Charles Navarro, Ian Hellings, and 
myself, there are over a dozen VWs and parts in a large, old factory... ideal 
:-) and take a look at one for yourself.  They fit together like a glove - they 
were CLEARLY designed that way.  And, by playing with the linkage long enough, 
I convinced myself that they're even designed to travel the full path to 
closing if the bellows are fully expanded. 

> BTW, as I was falling asleep last night I realized that it really 
> doesn't matter how much air is going thru the oil cooler when the 
> engine is cold, because there is little oil flowing thru the cooler 
> then. 

Exactly!  That was my (perhaps poorly stated) point - the flaps are only useful 
for heads and cylinders - any reference to them helping to regulate oil 
temperature (which I still maintain is NOT a "coolant" in the VW engine - if 
you want an oil-cooled engine, look at an old V12 Jaguar with oiljackets 
instead of waterjackets) is purely coincidental/accidental.  VW touted the 
pressure relief valve system as the method of oil temperature regulation.  It's 
well-documented in the BIG 1963-67 Bentley bus book (perhaps in other BIG 
Bentley publications as well). 

> > First off, one correction to what I stated earlier: all T4 used the 80-85C 
> > is it 85-90C?  I really don't remember offhand... I'll check next time I'm 
> > my parts and I'll check one).  Until 1974, the T1 used 65-70C, but 
> > they went to 80-85C.  I *think* that the T3 came with the 65-70C variety 
> > the factory, but on this point I could be wrong. 
> I believe you're right, but that's only a small detail.... 

For T1/T3, sure.  But for T4, it's very important - a 65-70C thermostat would 
overheat the oil. 

> I never heard the words hypereutectic or hypoeutectic, but I'm quite 
> familiar with the term eutectic, which refers to the ratio of 2 metals 
> which gives the lowest melting point of a binary alloy. 

Exactly - the eutectic temperature.  If a simple binary alloy with a different 
composition is raised to this temperature, it will split into two phases - one 
liquid and one solid and each with a different composition.  One of them is 
pure and one isn't and I forget which is which offhand... 

Thus 63%Sn 
> / 27%Pb is the tin-lead eutectic and 72%Ag / 28%Cu is the silver- 
> copper eutectic. What you have defined above just sounds like the 
> concept of a saturated and a super-saturated solution. 

True.  But metallurgists are a strange blend of formally book-trained 
analytical engineers and less-formally trained people with gobs of actual 
metallurgy experience, resulting in a fun blend of what a purist would call 
both "proper" and "improper" nomenclature.  The terminology I used is correct 
and is even used in books now, but interestingly enough I have only ever heard 
it referred to in the real world that way by aluminum metallurgists. 

> I found properties of similar alloys at: 
> http://www.shef.ac.uk/uni/academic/D- 
> H/em/SSM/briteproperties.htm  (sorry about the line break) 

Interesting info! 

> They show an alloy with 17% Si that reduces the expansion 
> coefficient by about 13%. While I have to agree that this is 
> certainly significant, it really just reduces the steel/alum alloy ratio 
> from just above 2 to just below 2. Still, it's a step in the right 
> direction. 

Those figures are at one temperature.  Especially with aluminum alloys, the 
coefficient of thermal expansion is pretty dependent on temperature.  For 
example, Aluminum 201's CTE (thanks to high Cu and low Si content) goes up 
significantly with temperature whereas 356 most certainly does not, so while 
the figures for 20C or whatever it is look quite similar, they behave very 
differently.  (BTW, can you keep a secret?  Aluminum 201 is what Autocraft uses 
for their ultra-expensive racing heads due to good high temperature strength.  
I wonder how well they seal against the cylinder, keep the valve seats in, or 
pull the studs tight... I know that I'd be a little skeptical to pay over $1000 
a head to get something that was engineered this way!) 

We can look at the book numbers until we're blue in the face, but we're missing 
the simple result.  The fact is that the modern automotive industry at both the 
OEM and racing levels has taken a VERY prominant note of this difference and is 
liking the idea of the cast 390 alloy now over forged 2618 due to decreased 
piston/cylinder clearance more and more.  I'm very tempted to use Keith Black 
pistons in my new cylinder set for just that reason, but am scared that a) they 
have no aircooled experience and b) they have a reputation among some engine 
builders as having poor QC.  I'll stick with old-tech JE forged ones for now... 

> They also show other alloys with up to 40% Si which have even 
> better (lower) expansion coefficients. One wonders how good their 
> other properties are, however, as the ones they choose to display 
> don't tell the whole story. 

One thing: with that much Si, the alloys become more and more brittle.  390 
only has 16% Si, but at that it still has <1% elongation.  Perhaps extreme loss 
of ductility has to do with it... 

> Some of the other material on these pages indicates that these 
> aren't really alloys at all, but two-phase materials like glass fiber 
> and epoxy resin. That's a pretty neat direction to be going! 

A lot of aluminum pistons have steel inserts in them to control expansion, for 
example a stock Mahle 914 2.0 piston. 

> I agree, pretty neat. All in all, the state of metallurgy is just 
> advancing out of the dark ages. 

Materials Science fascinates me, too.  I was contemplating majoring in it for 
quite awhile... 

> I don't remember for sure either. I don't see why a long warm-up 
> period would make a head crack. I'm just convinced that the 
> warmup period is a time of high wear rates on things like pistons, 
> cylinders, rings, and bearings, because of poor clearances when 
> cold and poor lubrication from oil that is still too thick. 

Yup, agreed.  The flaps helps the pistons/cylinders and the pressure relief 
valves help the oil. 

> I've got a cute little book from decades ago that is titled something 
> like "Designing for Alcoa Castings." In it, they point out that 
> magnesium sometimes has the advantage when there are large 
> thin walled sections in the casting. If cast in Al they could 
> theoretically be made thinner, but the wall would be likely to fail 
> from buckling, while the Mg could be thicker, thus resisting the 
> buckling, without a weight penalty. 
> OTOH, I see that the thermal conductivity of Mg is only a little 
> more than half that of Al. Maybe the alloys are closer than the 
> figures I have for the pure metals.... 

Judging by the difference in thermal expansion of Al vs. Mg, that advantage of 
Mg you quoted earlier makes sense.  One problem with Al castings is that when 
they cool down unevenly, they also shrink unevenly, resulting in latent 
stresses.  If you design a casting poorly then go to machine it, you can 
relieve the stress the wrong way and watch the casting crack!  Perhaps the 
explanation you just read means that although Al is technically stronger (i.e. 
can theoretically be thinner), the wall would fail due to latent stresses 
created during the casting process.  There are ways to help this problem, 
including adding heaters to alter the rate of cooling, but that gets 

> > But all that is speculation.  I am curious to know exactly what 
> > their reasoning is... 
> Certainly a healthy dose of curiosity is good for each of us.  ;-) 

Yeah... I need to get back to work!  :-) 

> Micah is right, however, if the rain stops, we may take a break and 
> walk down to Babcock Hall where the Dairy Science makes and 
> sells the world's best ice cream. 

Can I get cookies and cream? :-) 

Take care, 

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