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A J-tube is just like a heat exchanger but minus the heat exchanger. The
only draw back is that you can't warm the cabin in cool weather. It won't
affect the engine cooling (see note!) since the pipes are not close enough
to the valve covers to radiate heat enough onto them to make a difference,
not to mention that most of the time air is flowing between the two.
If you want you can have the tubes ceramic coated or you can wrap them
yourself with header-tape/exhaust-wrap/turbo-wrap or whatever it's known
by. It's just an insulator that's easily applied like a knee or ankle
bandage and it lessens the heat radiated from the material it's covering.
----------------------------- NOTE -----------------------------
If you put the J-tubes on that means you will be removing some components
of your heating/cooling system. This system is also a vital part of the
engine's cooling system! You will need to plug up the holes that lead into
the cabin so dirt and water don't enter in. You will probably want to
remove the pre-heat tubes since they won't be in use any more (but keep the
parts 'cause you never know when you may want them again). The fresh air
hoses that direct air from the fan housing to the heat exchangers will be
removed and this suddenly causes a BIG problem to the engines cooling
ability!!! You MUST now plug these holes on the fan housing where the
fresh air hoses connect. Not doing so will allow all the air drawn in by
the *cooling* fan to be expelled to the outside again with out passing over
the engine -- you will end up cooking your engine!!! Now, on cold/cool
days when the engine is just starting the temp control flaps will be closed
(to allow the engine to warm-up), however, air will not be forced past the
flaps and cause poor warm-up since it's JUST LIKE the heating system was
turned off (cabin flaps to allow air in are closed).
You can go to a muffler shop and have them make you a pair of caps to cover
the holes -- the cost should be under $50 (welcome to the world of
customization :). Just make sure the neck of the cap is about an inch or
longer and the cap is welded to the neck completely to keep air leaks down.
You can attach the cap by drilling a hole through both sides of the cap
neck and into both sides of the pipe from the fan housing. Then use a
long, narrow bolt to secure the assembly. Be sure to use a washer with the
nut to keep it secure (does anyone know if it'd be okay to use a
self-locking nut, would it withstand the heat?). If you can find a way to
use some kind of clamping device it would be better as the bolt holes in
the fan housing will become slightly deformed over time as the metal is
soft. This is *very* minor but because of this I don't recommend using
sheet metal screws to hold it down (I speak from experience as I have
designed a superior air exchange on my baby since I kept blowing apart the
flimsy stock hoses).
-- Diagram of what I'm trying to say --
(Do the same for the other side)
bolt--> ### |neck of cap
neck air hose attaches to| ___#___V_
\________________V_____#__ |
# | <--cap
<--to fan housing # |
____________________#__ |
/ ___#____|
/ _#_ <--washer
/ ### <--nut
#
Standing behind engine looking at the right side
----------------------------- END NOTE -----------------------------
It sounds complicated and time consuming but it's really not and it's
really easy (really!). Make an appointment if need be and drive the car to
the shop. Unclamp one hose and use that side to test the cap. Make a
duplicate for the other side. Reclamp hose, drive home, unclamp hoses,
position caps, drill holes, bolt in, done. Now just remove the other stuff
and put on the J-tubes. Muffler shops have all kinds of cool tools for
cutting, expanding and welding metals and this task would be a breeze for
them!
Put 'em on as you won't do anything to your engine except make it a couple
pounds lighter :)
Toby Erkson
air_cooled_nut@pobox.com
'72 VW Squareback 1.6L modified to 2.0L
'75 Porsche 914 stock 1.8L
______________________________ Reply Separator _________________________________
Subject: t-3 heat exchangers
Author: type-3-errors@umich.edu at SMTPGATE
Date: 1/24/97 2:41 AM
I have a 72 Squareback, the heat exchangers were shot so I went out and
bought a pair of J-Tubes.I was wondering if it's a good idea to put them
on.Do the J-Tube interfere with the smog system on the car, like the EGR?Is
ther any drawbacks in running J-Tubes, does it effect the cooloing of the
engine?
Casey Engel
--72 squaeback
--82 Cabriolet