The reason I was confused is you seem to be one of the first to have purchased the redesigned thermostat now sold by flow cooler. What ever caused them to create such a disaster only insanity can explain but they are now offering a new restrictor plate that matches a new diameter hat on their Cleveland thermostats. Not a duplicate of factory but their own self-designed version. 😳😳
The only reason I know this is a Posting Mike Drew made to the email list this evening, as follows :
The Robertshaw 333-180 is the ultimate thermostat for the 351C—or at
least it used to be.
There has been an undocumented design change with the same part number.
Now, instead of supplying a thermostat with the 351C ‘hat’ which
partially (but not fully) blocks off the orifice in the center of a disc
pressed into the block, instead they are supplying a conventional Windsor
thermostat (ordinarily bad news) along with a replacement disc with a
smaller (too-small) orifice. In order to use this thermostat the stock
disc needs to be removed from the block and replaced with this new one.
That then means that going forward only NON-Cleveland thermostats can be
used. If a proper 351C thermostat is installed, it will be prevented from
fully opening because the hat will strike the now-too-small disc.
With this new setup, when the thermostat opens it will fully block off
the orifice. However, the engine is supposed to have at least some water
circulating past the disc, with an area equivalent to that of of a
5/16ths bypass hose as used in other Ford engines. (If you compare the
size of the stock ‘hat’ with the hole in the stock disc, you will see the
hole is measurably larger). If I was to use this new setup, I would
therefore be inclined to modify the disc, either by drilling bypass holes
or (preferably) enlarging the center hole.
Too, the stock setup allows for some misalignment between thermostat and
disc. If the thermostat wasn’t perfectly centered, it would still have
room to fully open. With this new deal, if things aren’t perfectly
aligned, it might not fully open, or worse, it might open and get stuck
open, leading to very slow warmup problems.