Bob, I guess I had my brain in neutral when I said b voltagesb . O.K.,
input b pressuresb or whatever signal the factory used to calibrate them.
The Bourdon tube drives a mechanical movement for the needle, and it must have
some calibration adjustment. It has been a long time since I had a temp gauge
opened up, but most Smiths gauges have an internal way to adjust the
sensitivity of their response if you know which inputs to use.
212 is the normal position of the needle when the engine is shut down hot, as
I have observed on many BJ8s. My temp gauge has both sets of white dots. The
oil pressure side of the gauge, interestingly, has no dots unless the black
dot I see on the white 60 psi mark is a real dot. The fuel gauge has single
white dots near B<, B=, and B>.
If your concern is just to get a 180 reading while youbre on your road trip,
then why not just make the mental correction? What really matters is when it
changes from its normal steady state, mostly when it suddenly starts reading
higher than normal so you can check for actual overheating.
I think I read somewhere a comment by Geoff Healey that it was a mistake to
put numbers on the temp gauge. My MG Midget has only C (old), N (ormal), and
H (ot).
Have fun on your trip!
Steve Byers
HBJ8L/36666
BJ8 Registry
Havelock, NC USA
From: Bob Spidell [mailto:bspidell at comcast.net]
Sent: Sunday, May 27, 2012 11:08 AM
To: BJ8 Healeys
Cc: healeys
Subject: Re: [Healeys] Temp Gauge
re: " I believe the factory used
these calibration points with specific input voltages in order to make the
gauge reasonably accurate over its full range"
AFAIK, the gauge is entirely 'mechanical,' driven by expanding ether moving a
Bourdon tube. Thanks for the tip on the needle, I think if I can get 180 when
running stable I'd be happy.
I know the speedos have a 'calibration' point--a small white dot at about
(negative) 5MPH--but I don't see any dots on the temp gauge. Mine used to
read 212 exactly when I shut the engine down, so it was probably accurate
before.
Bob
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Bob Spidell - San Jose, CA
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