Looking at others' methods of attempting temperature stability on machines whose groups tend to overheat, I've seen various methods ranging from attaching a finned heat sink to the group to locking in a cold portafilter between shots to OE's "3rd Shot", which it seems they no longer sell.

The general idea is to add a heat sink to the group, and the portafilter seems like a simple idea and yet possibly underutilized with all that empty space in the middle.

Would it not be more effective to add some "brass mass" inside the portafilter when locking it in as a heat sink, filling it up with brass washers or a solid chunk of brass? (I am under the assumption that most of these portafilters are indeed made out of brass and then attempting to avoid galvanic corrosion by using the same material).

Getting a pile of brass washers from the hardware store seems like a low cost low effort way to make a more effective portafilter heat sink.
Another, more involved idea would be to wrap a finned heat sink around a portafilter, so that the ugly (IMO) thing wouldn't have to sit on the group the whole time.

Further thoughts?

It seems to me that temperature control methods need to be taylored to the machine.

Machines like the 1st and 3rd generation La Pavonis (1961-1974 and 2001 to date) are heated by bringing hot water around the cylinder liner. Water is only brought in when one moves the handle up and down, so one can heat them up quickly by moving the handle up and down after they reach pressure. In ordinary use the amount of water drawn in with each shot plus the heat that is brought in by conduction tends to make excellent espresso with out too much temperature control effort.

The second generation La Pavonis are a far great challenge (1974-2000). There are problems both getting them hot enough and getting them too hot!

To get them hot enough one needs to bleed them properly. Bleeding Pressurestat lever machines. (Especially 2nd gen La Pavonis) Failure to bleed them properly also results in "spongy pulls".

An espresso pulled just after thoroughly bleeding one of these machines, and then waiting until it comes back to pressure tends to be excellent. A second shot pulled immediately is likely going to be fine too, unless ambient temperature be really high.

Later cups will need cooling. One way is to get a ramekin and fill it 3/4 or so full of cold water, put it under the group with the lever all the way down, and then left the handle to draw the water into the group. Wait 5 to 10 seconds, bring the handle back down, and pull the shot. Each person needs to develop the technique for themselves at this point, but after the second all shots seem to behave pretty much the same, and require the ramekin before each.

The other technique is to turn off the machine and let it cool, with careful reading of temperatures and pressures one can also keep all shots decent.

The trouble with cooling fins on second generation La Pavoni groups is that as the fins cool the group, more steam rushes in because the cooling causes condensation. As more hot steam comes in its heat of vaporisation keeps the internal temperature of the space above the piston hot until the top of the piston is completely filled with liquid water.

So are you saying the OE "3rd Shot", an aluminum heat sink you lock into the group, wouldn't have been as effective in the 2nd generation Pavoni as it would have in other group styles?

As a side note I do use your ramekin/water draw technique and I like it.

The second generation, 1974-2000, machines really are tricky, but one can master them very well with practice. The third shot device might help some, particularly if it were to be very cold. The problem stems from the fact that brass is a fairly conducting metal and steam transfers heat to the top of the group at an extreme rate. The ramekin method cools down the bottom of the group very rapidly, you need to lift the handle enough so that some cold water gets pulled into the ramekin, I usually go for between about half way up and 3/4 of the way up. You must not get it near the point where hot water will begin to be expelled! I usually leave the water in the bottom of the group for 5 seconds or so, but a bit longer in summer. You need to pull the shot fairly quickly after the ramekin cooling. In fact, I tend to do it all at once. As soon as the handle is down and the ramekin is removed, I raise the handle just enough to expell a bit of steam, then lower it slightly, and quickly snap on the loaded portafilter, raise the handle all the way and pull the shot. I do not like to raise the handle with the portafilter in place because I do not like pulling air through the puck, and if I expell a bit of steam the space below the piston is mostly water vapour instead of air so I won't get a spongy pull.

The main advantage of the ramekin method is the extreme heat capacity of water per unit volume. A little cold water can cool something a lot. Contrary to how it sounds, the ramekin method is not messy at all. (Unless you drop it!)

I have to do more tests this weekend now that I am bleeding properly, but my earlier tests had the group cooling quickly with ramiken method but at puck temps relatively unchanged with or without the lower group cooling. Interested to see what happens with more testing.

Also after my first shot my et reads 106...

Finally question. You are saying that cooling fins cause the temp in the group to be so cool that it causes the steam to condense.

However the group is already under 100 degrees when pulling a shot anyway, so shouldn't the steam be condensing without a fin, until the group temp stabilizes at the boiler temp? I had also assumed that the group would be radiating sufficient heat that at swotch position 1 and the opv slightly purging the group would not likely ever match boiler temp exactly, am i terribly wrong?

You will have a tough time getting the top of the group up to the saturation temperature even with periodic lever pumping so it will always be full of hot liquid and a lower temperature than the boiler. This is the magic of a system that operates at saturation, the liquid and gas swap places with insignificant, almost unmeasurable, changes in temperature or pressure.

Thank you for your response. That is sort of where i was heading. Assuming the group never reaches the temp of the boiler, and assuming we are actively working to cool the group before pulling our shot- or pulling the shot before the group is too hot (obviously under 98c) then the steam would already be condensations and therefore the cooling fins would only improve on the efficiency of what is already taking place, rather than altering the process in 2nd generations as suggested above.

I recently added a small cooling fin to the upper pipe, slows the group temp slightly and makes the ramekin method a bit faster and more efficient, but am considering getting a larger fin for the main bel and/or a portafilter heatsink, so its a very relevant matter to me. Figure getting those and eventually using a teflon gasket would really create a much more stable group to work with.

The groups of the first and third generation La Pavoni machines will always be cooler than the boiler. That is NOT true of the second generation ones. Once the air has been removed so that water vapour is the only gas in the system, every point in contact with the water vapour will be at the same temperature. At 100C, 373.15K, the heat of vaporisation of water is 40.68 kJ/mol. It requires 40.68 kJ to vaporise a mole of water, and 40.68 kJ is released when the vapour condenses. When the pressure due to water vapour falls below the vapour pressure at a given temperature, it condenses and releases all this energy, so that keeps every surface at this temperate. Before the bleeding operation air in the group prevents water vapour from entering, or at least limits it. The steam passage is small so a very long time is required for the air to diffuse around. But one cannot control how much air there is in the system, and it keeps changing, making erratic temperature behaviour in a poorly bled machine.

In the first and third generation La Pavonis the group internals are NOT immersed in water vapour as they are in the second generation (1974-2000) ones. Thus the first and third generation la Pavonis are VERY different animals when it comes to temperature control.

"The general idea is to add a heat sink to the group, and the portafilter seems like a simple idea and yet possibly underutilized with all that empty space in the middle.

Further thoughts?"

The portafilter will transfer heat to or from the group very slowly, because of the very small surfaces available for heat conduction:
1) brass to brass only on the contact area between the portafilter tabs and the slots in the group
2) through the stainless basket and the rubber o-ring from the upper lip of the pf.

This can be demonstrated by holding the pf with your fingers after attaching it to a hot group. Unless you wait quite a while you do not burn your fingers.

A cold portafilter is much more effective in cooling the coffee which flows through it when pulling a shot, and is very good for making iced lattes.

On my Stradivari, a cool PF brings the external temp of the group down by 10F in less than a min.