Carl and Scions,
In an about face of my opinion, I am questioning the benefit of the sleeved
thermostat, over a bypass restrictor for my newly rebuilt engine. Actually
I have been questioning it for a month or so, but Carl's post on building
his own sleeved thermostat gave me the little push to make the measurements
and publish my thoughts.
History: Several years ago a NJTA club member, Bruce Hoppe, bought a
sleeved thermostat from XK's Unlimited (www.xks.com or 800-444-5247), with
the thought that it looked like it might fit a TR3 thermostat housing. It
did and I bought one too. I also alerted the list (and Moss and TRF) to
this new device. Moss recently began buying these from XK's and put them in
the catalog.
I've used the sleeved thermostat for several years now, but still used a
bypass restrictor. I was recently directed to an excellent 160F (unsleeved)
thermostat (the Robertshaw 330-160, Highflow) by Brian Schlorff, another
lister. I immediately realized that the XK's sleeved thermostat is based on
this same thermostat. This was confirmed by the presence of the Robertshaw
part number, 330-160, on the XK's sleeved thermostat. (Carl, that was for
you.)
IMHO, the sleeved thermostat is not required, IF you use a restrictor in the
bypass (I have used a 3/8 previously and I am now using a restrictor with a
1/4 inch diameter hole in it).
If you go into a speed shop and ask for a Robertshaw 330-160 Highflow
thermostat, you will get the right thermostat for $6 to $8, but you should
fit a restrictor in the bypass hose to keep the water flowing to the
radiator, not through the bypass loop.
The primary logic for my decision that the skirted thermostat is not
required is that the cross sectional area of the bypass restrictor (1/4 inch
diameter), is significantly less than the area left open between the
thermostat skirt and the thermostat housing, when the skirt is fully
extended to cover the bypass hole. This means that my restrictor is
determining the water flow, not the skirted thermostat. I am making this
judgement based on only two thermostat housings, but it would be interesting
to see if others measured the same thing. I know of at least one other
lister, with a TR3B, who felt the skirt didn't quite cover the hole well
enough.
The bottom line, for me at least, is that using the Robertshaw 330-160,
which has a noticeably larger water passage than most thermostats, with a
bypass restrictor, is all I believe I will need. BTW - the 160 in the
Robertshaw Part number is 160 degrees F. They make a 330-180, which,
obviously is a 180F thermostat, if that is what you want.
BTW - If you really want a sleeved thermostat, buy it directly from XK's and
save some $$$$'s over Moss's price. XK's makes the Moss Thermostat.
Sorry about my 180 degree turn around in thinking, but the physics of the
situation says it all, for me. The sleeved thermostat won't hurt your
cooling. I just don't believe it will help as much as a bypass restrictor.
My personal thanks to Bruce Hoppe, for initially finding the sleeved
thermostat, and Brian Schlorff for pointing out the Robertshaw Hi-Flow.
Jack (back on the road in two weeks) Brooks
1960 TR3A
1974 Norton 850 Commando
Hillsdale, NJ
My car show: http://NJTriumphs.org/westwood/home.html
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