[Vwdiesel] Burned out glow plugs

[Sandy Cameron]

My theory about overstressing and burning out glow plugs by boosting, (with
cables and a donor vehicle, or a big shop charger)  is now proven !

Yesterday I went to pick up my 94 A3 at a shop where I had some mechanical
work done that my ancient body would not let me do at home.

I completely trust the people at the shop in most things, but this
phenomenon is a bit arcane and consequently not fully understood by many.
Besides, I burned out the plugs. 
Should have known better.

The situation:

-94 in for a clutch job (long overdue)
-Manual glow plug button (automatic system failed 3 years ago)
-Weather very cold, (-16C, 0F)
- Junior forgot about the manual glow and killed the battery.
-Car pushed in to shop, work done, 
-Car started OK (warm shop)
- Car run outside and parked, battery not recharged much.(presume test drive)
-Cold soaked for a day or more.
- I arrive and try to start it, would barely turn over.

- I plan to jump it from friend's passat, but proprietor offers high rate
shop charger.(never did like those things) Albeit set to low rate to thaw
battery, Also plug in block heater, retire to warm shop for chat.

When we come out again, battery is still slow cranking, so Prop. switches to
"boost " mode.

I'm a bit nervous about this, so I switch on the dome light and watch it
while I push the glow button (wired to the original  glow relay, not direct)

Within 10 seconds, I notice the dome light flickers and gets brighter, I
crank and engine stumbles to life, I quickly  dump the glow. I think, but do
not say, that the high boost fried some plugs. I get home, let it run for a
while to recharge the battery and warm everything up.
then shut it down.

About 6 hours later, I go out to move it in from the edge of the road for
the night (passing drivers have swung in to my driveway, ended up on the
lawn, etc in the past) Car is reluctant to start, stumbles, classic example
of some plugs non-functional.

Get it in to the shop and break open the joint to the individual feed wires
(my split feed mod that replaces the bus bar) takes 20 seconds, get out my
heavy ammeter and test each plug... 2 are dead, #1 and #2, the most
miserable to change.

You don't have to be a space shuttle engineer to interpret small details
(dome light that flickers and gets brighter)  that anticipate disaster.

I had concluded some time ago that I had bown some glow plugs while trying a
boost start an A2 from an assisting vehicle which was running at high idle
for best alternator output.

Bosch rates the glow plugs at 11 volts, which they are lucky to get with a
healthy battery and cold weather in normal sub-arctic conditions. A running
donor car will produce 13.6 volts with some enthusiasm, from its alternator,
and a boost charger can do even more.
20% over voltage for the plugs.

These cars will start in those conditions if the battery, cables, and oil
are in good condition.
they do sell them in Scandinavia. (and Minesota?)

This car has always been a good cold weather starter, even if it was "Hecho
en Mexico" after a Tequila break.

I would suggest the drill would be, to FULLY charge the battery over several
hours at a reasonable rate, use the block heater if possible, and DO NOT use
external boost of any kind for the actual start.
 
The one exception to this would be replacing the battery with a fresh, fully
charged one, and/or paralleling another with heavy booster cables.

Such a fresh battery could be a donor vehicle, WARM AND FULLY CHARGED, along
side, BUT NOT RUNNING.

This would provide the necessary glowing and cranking current without the
high voltage that will shorten the life of the glow plugs.

Not being the owner of a computerized car of any kind, I would wonder if
this could be a problem for them? High boost chargers, or boosting from a
running vehicle?

My story ends. Replacement of plugs begins.......

Sandy