I have no experience with Heet or the STP product you mention...

2) Apparently works well for its intended purpose, but I prefer not to
use it due to the possibility of reduced heat transfer and/or clogged
heater cores.

3) Supposedly an excellent fuel system cleaner but should be unnecessary
if you start with a clean engine in good tune and only use good, brand
name gasoline.

I'll add a plug for one other product that I've used with success; GM's
"Top Engine Cleaner."  Now available in spray cans, on an old carboned
up engine does remove some carbon (but will lay down a nice smokescreen
while doing so.)  It is available at my FLAPS as well as I assume GM
dealers.

For the most part I don't feel the need to use any other
additives/supplements, although I do have two bottles of AutoRX that I
bought because of the surprising (given the nature of the product)
number of glowing reviews on BITOG.  I was going to use it to clean out
an old Studebaker V-8 that ran sweet but was sludged inside; however,
when I tore the engine down to put new gaskets in it, I found enough of
a ridge at the top of the bores that instead of a quickie gasket and
seal job I ended up simply replacing the engine with a freshly rebuilt
Avanti engine that my friend conveniently had on the shelf - hence, I
still have the unused AutoRX, since my Porsche has had a steady diet of
synthetic for years so I assume that the engine should be clean inside.

Which reminds me; the Avanti engine didn't come with rocker shafts, so I
reused my old ones - I meant to get some rebuilt ones (they're known for
passing lots of oil and letting the heads fill up with oil at high RPM
when worn) but have never ordered them due to other things going on.
thanks for reminding me!

nate

Methanol. Don't need that sh.t if you keep your gas tank topped up as
much as possible all the time.

Bad, bad sh.t. Only use if you're trying to unload a car on an
unsuspecting buyer before it sh.ts itself all over the driveway
(the car, I mean).

Good sh.t. Use as desired. Buy the big bottle.

Bad, bad sh.t. Only use if you're trying to unload a car to an
unsuspecting buyer before it sh.ts itself all over the driveway
(the car, I mean).

And hey, if you're trying to use these magic potions to sneak a junker
past the leasing people, most likely it won't work. They've seen that
before. Many, many times.

Of that list Techron and Heet seem to do what they advertise. Bars-leak
is the most harmless of the stop-leaks and is OK in an emergency. Oil
stop-leaks are a bad idea because they do long-term damage to gaskets,
although they sometimes do "sorta work" by making the gasket swell a
little in the short term.

If you need reduce moisture in gasoline this might do the trick.  A
far better solution would be to solve the cause of the problem.  I
live in an area where summers are very hot and humid and moisture
buildup has yet to be a problem in either my cars or lawn mower.  For
most of us this is probably a waste of money.

In an emergency when the leak isn't major it will work.  It is not a
permanent solution though and if the cooling system is partly plugged
up from minerals, etc., a hole sealer might make things worse.

A waste of money considering how highly formulated gasolines are
already.

I've used leak stoppers on several older cars, and as with other fixes
in a bottle they will hold the problem at bay for a while.  They are
not a permanent fix though.