-- [ From: Bob Nogueira * EMC.Ver #2.10P ] --
Issue:
>temperature sending unit. On the Z Magnette it is an electrical
sending >unit, so the MG "specialist" substituted a unit for a late
model MGB. >Unfortunately the unit does not work with the Z Magnette's
water >temperature gauge, staying on "cold" regardless of the driving
conditions. Reply:
If the Gauge is a Smiths 4 in one type it is the same as used on the
Morgan Plus 4 . When mine went belly up I disassembled it and
received a education on how it worked .
The sender is not a resistor but contains a bimetallic bar wrapped in
nichrome wire ( toaster wire). at the end of the bimetallic bar is a
set of contact points which ground the wire.
Mean while back at the gauge is another bimetallic bar wrapped in
toaster wire. Juice is fed in the the gauge, out the gauge to the
sender unit ( shouldn't it really be a receiving unit?) and to the
toaster wire . the wire at both ends heats the bimetallic bars which
bend, at the gauge the bar is attached to the needle, at the sender it
opens the points , breaking the current allowing the bars to cool . As
the coolant heats the sender units bar takes longer to cool than the
gauges bar thus the needle returns faster toward the "off" position
HOT .
Thus the unit does not reduce current flow as the sender heats up it
interrupts it . The hotter the engine the longer the interruption.
I never could find a sender from any other car that would work. ( It
should be noted that the engineer who designed the system for SMITH was
fired shortly after its introduction and went on to a high position at
LUCAS.)
My solution was to strip a gauge which had the same needle span a the
Smiths and mount "inards" in the Smiths case.
If anyone has a sending unit available it will be Melvyn Rutter at
The Morgan Garage
Little Hallingbury,
Near Bishops Stortford
Herts England CM22 7RA
Tel 0279 725725
BOB, "Bill GATES is a THIEF"
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