Q: My rear window has
a strip of glass that doesnít defrost like the rest of the window.
It bugs me because itís right in my view behind the car. What can
be done to fix this?
A: It sounds like one
of the slender printed conductive stripes on your rear glass has
been scratched, severing its electrical conductivity. Itís
possible, using a Permatex 09117 Complete Rear Window Defogger
Repair Kit or similar, to repair a broken spot in these stripes. If
careful visual inspection doesnít indicate the point of breakage,
an inexpensive multimeter can be used to identify the exact
With the window
defogger turned on and the multimeter set to DC volts 20, connect
the black meter lead to bare metal on the body, such as a door latch
striker. Then gently touch the red lead tip to each stripe, one at a
time, near the center of the glass. A functioning stripe will
indicate roughly half of the vehicleís system voltage ó about
6V. This is because the stripes are long resistors and drop voltage
along their length, from the source side (12V) to the ground side
(0V). If you find a stripe that reads either 12ish or zero near the
center, youíve found the bad one!
Next, move gently
left or right, probing that stripe, until the voltage abruptly
changes. Search for the exact spot where you find 12ish in one
place, and zero right next to it ó this is the break! A full
voltage drop in one place occurs because current isnít flowing
through that circuit. Apply a piece of tape directly above or below
to mark the spot and break out the kit.
The kit consists of
instructions, a cleaning pad, stencil, a slender brush and a bottle
of conductive paint to apply over the scratched stripe. Also
included are materials to re-bond a broken wire tab, if needed. You
may find firmly applying your own pieces of tape may more accurately
match the width of the stripe, and the paint color may not match
exactly. Also, if sufficient thickness isnít built up (three coats
are recommended) the repair spot will heat a bit more than the rest
of the stripe, defrosting a little sooner than elsewhere. If applied
carefully the repair will work and is only slightly noticeable.
Q: How often should
brake fluid be replaced? Itís not listed in my maintenance
schedule. My oil change guys are trying to sell this!
A: This is an
interesting topic, as some manufacturers are all over this,
requiring fluid replacement every two or three years, or by mileage
such as 30,000 or 45,000, while others imply itís never needed!
Brake fluid lives in a fairly sealed environment, but by its nature
absorbs moisture, and its fluid additives break down over time.
Moisture buildup lowers the boiling point of the fluid, leading to
possible high temperature braking loss, and coupled with additive
losses, encourages corrosion and gunking of some potentially
expensive ABS parts.
Brake fluid typically
darkens in color with age, from either clear or honey color to a
deeper brown, but this isnít a reliable indicator of true
condition. Test strips are available to check both moisture and
copper content; the latter is an excellent indicator of fluid
additive depletion and system corrosion. As you found, quick lube
shops may also check condition for you in the hopes of selling a
flush. I flush/replace fluid on my vehicles every three or four
years even though itís not listed in the book. ABS systems can
complicate fluid replacement, often times requiring the use of a
scan tool to shuttle various valves in the right way to pass fluid