The original thermostat in my 1951 MGTD MKII is defective and a similar
type is no longer available. What should I do? Please bare with me as I
explain in somewhat detail; history and what has been done to date.
When I purchased the TD, the thermostat was the removable type, it had a
center brass bolt which bolted to a cross arm in the upper parts of the
housing. The bolt was affixed to 1) a 1 7/8 inch diameter, 5/8 inch high
brass band (which affected the flow in the bypass tube) and 2) to the
thermostat diaphragm. The bottom of the diaphragm was bolted to a 2 inch
diameter flat ring via three supporting arms. This lower ring fitted
into a grove in the housing. To install, the thermostat was inserted
through the bottom of the housing until seated and the top bolt was
inserted in the crossarm and the nut tightened.
The thermostat was inoperative when I purchased the car. The previous
owner had soldered the diaphragm in the compressed (open) condition,
saying that driving in Florida, the thermostat would be open all the
time anyway. He emphasised the need for some restriction in the water
flow path.
When the engine was rebuilt in January, the machine shop saw the
soldered thermostat and junked it; ie. returned the TD with no
thermostat installed. I have the old thermostat but it is in pieces; i.e
butchered.
Being advised I should not drive the TD without a restriction in the
water flow, I ordered a thermostat from Moss (also tried Abingdon, but
they had none available). The Moss thermostat was completely different,
just a flat circular plate with a small thermostat system protruding
from the center. The replacement fit loosely in the grove in the bottom
of the thermostat housing, so I flattened the raised edge to make it
more snug.
I am concerned about the thermostat since I am about to make a 5,000
mile trip in the TD. I was about to order a housing with non-removable
thermostat from Moss, but would like advice first to know if this
expense is really necessary.
Last night I read over 200 archived messages about thermostats. The
common thread is that you should have some restriction in the bypass
outlet. The original unit provided this with the brass band, but the
Moss replacement does not provide any restriction. Is control of the
bypass really necessary if I am driving in a hot climate all year?
I ask if it is really necessary because I have now driven approx 4,000
miles with the Moss replacement thermostat installed and with no
restriction in the bypass outlet. Much of the driving has been in
Florida, but even here my water temperature gauge (rebuilt several
months ago by MoMa) never registers higher than 83 deg C, usually in the
mid to high 70s. The water temperature seems to be okay, so should I
even be worrying about the quasi thermostat installation in my TD. Am I
just being a perfectionist and a worry wart?
I am not even sure I installed the replacement thermostat correctly, but
it seems to work. The unit is marked with the words "TOP" on the ring,
with the spring and housing protruding below. This is how I have it
installed. However, there is an annotation on the side saying "Flow" and
an upward arrow. What is the direction of water in the system? Is water
coming from the top of the engine, UP into the thermostat housing and
then into the top of the radiator to cycle downward and be cooled. For
some reason I thought it was the reverse. Shows how little I know about cars.
I am listening to all advice, such as
1) leave well enough alone, the water temperature seems to be okay now
2) order a housing with non removable thermostat from Moss
3) put some kind of restriction across the bypass opening as suggested
by some of the archives.
Thanks for your patience in reading all this detail, for putting my mind
at ease and for any suggestions.
Stu Keen
Venice, Fl
simbafish@home.com
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