[E-Type] V12 Charging/Starter Problem

While my '67 S1 FHC is out having new brakes installed, I have been driving
the '74 XJ12L–which I am sure shares many of the same components and,
therefore, problems with the powerplant in the SIII E-Jags.

I have a problem with the charging system, or else the starter is going.
When I drive the car for a short time (10 minutes or so) I can turn the car
off and the re-start it. When I drive it for a longer time, say 20 - 30
minutes, which gets the car good and hot (never overheats per the gage) and
then turn off the car, I can’t restart it without a jump.

I just replaced the battery, and it did not solve the problem.

My thoughts are either: A) the alternator is not charging the battery
sufficiently to allow it the charge necessary to re-start the car, or B) the
starter is getting a bit “weak” and when hot things are expanded and it
can’t turn over without a bit of extra voltage from a jump.

When the car has been driven 20 minutes and is good and hot, and I have the
AC on, the radio on, and the lights on, at idle the output of the alternator
is 12.78 V, 30 Amps, Diodes Good. (readings per the battery shops fancy
electronic testor). At 2200 RPM, everything on, Hot car, the output rises
to 13.6 V, 30 Amps, Diodes good.

Anyone out there that might have had this same experience or have an idea of
which component I next tackle?

Thanks,

Tom H.
'67 E, '74 XJ12______________________________________________________
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In reply to a message from Tom Heinrich sent Sat 14 Aug 2010:

Dear Tom,
with a carburettored v12, when trying a hot restart as you
describe, I have always found that flooring the throttle was the
only way to get it fire up quickly. As soon as it fires, lift your
foot off…
kind regards
Marek–
MarekH
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In reply to a message from Tom Heinrich sent Sat 14 Aug 2010:

The output numbers seem just fine, have the battery place use
it’s fancy electronic tester to see current draw of the
starter cold and hot. 30 amps seem like a low output for a
car with A/C but if that’s what’s been there forever who am I
to suggest something better…

Lester–
The original message included these comments:

When the car has been driven 20 minutes and is good and hot, and I have the
AC on, the radio on, and the lights on, at idle the output of the alternator
is 12.78 V, 30 Amps, Diodes Good. (readings per the battery shops fancy
electronic testor). At 2200 RPM, everything on, Hot car, the output rises
to 13.6 V, 30 Amps, Diodes good.
Thanks,
Tom H.


http://tinyurl.com/mqlgly '66 4.2 FHC
Louisiana, United States
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In reply to a message from Tom Heinrich sent Sat 14 Aug 2010:

Hi Tom,
Does it have the OPUS system like the V12 E’s? If so that
seems like a common failure mode for the OPUS unit. Some
people have tested it by placing a bag of ice on the unit to
cool it, if it starts then you have your culprit. I’ve also
heard of weak starters failing with heat, did you say if it
turned over? If it doesn’t turn over then I’d look at the
starter.
Good luck,
Lynn–
Lynn G.
68/85 ots, 73 2+2, Boise, Id., United States
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