A few comments:
Piezo heads which Epson uses do not require cooling to protect them,
since they do not heat up to any extent during the printing process.
Unlike thermal heads which apply a current to a resistor to heat the
head nozzles to cause the heat to boil to project it, piezo is a
mechanical pumping action that moves the ink, and is why Epson printers
can be used for so many types of ink formulations.
Some higher end Epson printers do have some thermal sensors, but they
are there to sense the head temperature to help determine the ink
viscosity to regulate the dot size more accurately by changing the
duration of the pumping action of the piezo actuator.
The 740 exclusively used dye colorant inks inks. In general, making
inks insoluble when dry adds to their cost besides creating
functionality problems with these types of dye ink printers. I would be
suspect of 3rd party ink manufacturers using ink components that would
be more costly and make the ink work more poorly in these type of printers.
It is true that all inks when left dried in the head for long period of
time become more difficult to dissolve and that is why I suggest a
mixture which contains ammonia, glycol and alcohol which wok as wetting
agents, softening agents and detergents. The one thing that must be
emphasized with these older printers is that it will take time,
sometimes a week of head soaking and printing with cleaning cartridges
to get the heads clear. This would be the same with either OEM or 3rd
party inks.
The advantage of the 740, was one example, is it is pre-chiped, so the
cartridges are very inexpensive, easy to refill at home, and do not
require an chip resetter. The 740 was a reasonable printer, well built
using only 4 ink colors. Not as good as current models in terms of ink
drop size, and many ink colors, but a reasonable printer for text,
graphs and such, and a acceptable photo printer with the correct paper
types. It is very inexpensive to keep filled with ink.
Art
If you are interested in issues surrounding e-waste,
I invite you to enter the discussion at my blog:
http://e-trashtalk.spaces.live.com/