[DeTomaso] Interesting Robertshaw 333-180 thermostat design change

[Mike Drew]

Bud,

Great question.

The Cleveland thermostat is designed to block off most of the water from circulating around and around in the engine once it opens up. The hat fills most of the hole, so most of the water goes forward to the radiator, and only a bit continues to circulate in the engine (promotes even cooling and helps prevent hot and cold spots).

The Windsor thermostat protrusion is too small so it allows too much water to circulate in the engine and bypass the radiator.  Often a 351C with a Windsor thermostat will run sort of okay temp-wise at freeway speeds, but invariably it will overheat at low speeds. All the radiator/fans in the world does no good if the water never reaches it. 

Too, if the orifice is blocked off completely/permanently, water will not circulate at ALL until the water near the thermostat heats up enough to open it up. By that time there could be localized hot spots or steam pockets elsewhere in the engine, which can lead to blown head gaskets etc. 

When the thermostat eventually opens in that case, the hot water goes forward and unadulterated cold water enters the engine from the completely cold radiator. WHAM!  The block experiences thermal shock. The cold water will reach the thermostat and it will snap shut, then the water in the motor will heat up (too much) again, over and over until eventually equilibrium is reached. 

You can mitigate this by at least drilling a hole in the device you use to block off the orifice, so that some water circulated through the engine at all times. 

But the real solution is to RESPECT the designers who created the cooling system, by using a proper Cleveland thermostat and disc (and making sure the air is bled out of the system, or else all bets are off....)

Cheers!

Mike

Sent from my iPad

> On Nov 16, 2019, at 20:47, B Hower <b.hower3400 at yahoo.com> wrote:
> 
> Dear Mike,
> 
> What do you say happens, if one uses a Windsor style thermostat ( no hat, full flow style as the true Robertshaw 330-180 ) and the OEM disc?
> 
> I am sure this has come up in the past, but I need a refresher course.
> 
> Please help,
> 
> Bud #3400 ( Drive it like there is no tomorrow -- for there may not be ! )
> 
> 
> 
> 
> On Saturday, November 16, 2019, 10:04:00 PM CST, Mike Drew via DeTomaso <detomaso at server.detomasolist.com> wrote:
> 
> 
> All,
> 
> 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. 
> 
> Here is a pic of a ‘real’ Robertshaw 333-180 compared to the new one:
> 
> 
> Here is the new one with its included disc:
> 
> 
> 
> And the disc laid over the thermostat:
> 
> 
> 
> I’m sorry I don’t have a stock disc handy to compare, and show the clearance between the orifice and the hat. You will just have to take my word for it....
> 
> Mike (hoarding his one remaining good thermostat!)
> 
> Sent from my iPad_______________________________________________
> 
> 
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-------------- next part --------------
   Bud,

   Great question.

   The Cleveland thermostat is designed to block off most of the water
   from circulating around and around in the engine once it opens up. The
   hat fills most of the hole, so most of the water goes forward to the
   radiator, and only a bit continues to circulate in the engine (promotes
   even cooling and helps prevent hot and cold spots).

   The Windsor thermostat protrusion is too small so it allows too much
   water to circulate in the engine and bypass the radiator.  Often a 351C
   with a Windsor thermostat will run sort of okay temp-wise at freeway
   speeds, but invariably it will overheat at low speeds. All the
   radiator/fans in the world does no good if the water never reaches it.

   Too, if the orifice is blocked off completely/permanently, water will
   not circulate at ALL until the water near the thermostat heats up
   enough to open it up. By that time there could be localized hot spots
   or steam pockets elsewhere in the engine, which can lead to blown head
   gaskets etc.

   When the thermostat eventually opens in that case, the hot water goes
   forward and unadulterated cold water enters the engine from the
   completely cold radiator. WHAM!  The block experiences thermal shock.
   The cold water will reach the thermostat and it will snap shut, then
   the water in the motor will heat up (too much) again, over and over
   until eventually equilibrium is reached.

   You can mitigate this by at least drilling a hole in the device you use
   to block off the orifice, so that some water circulated through the
   engine at all times.

   But the real solution is to RESPECT the designers who created the
   cooling system, by using a proper Cleveland thermostat and disc (and
   making sure the air is bled out of the system, or else all bets are
   off....)

   Cheers!

   Mike
   Sent from my iPad
   On Nov 16, 2019, at 20:47, B Hower <[1]b.hower3400 at yahoo.com> wrote:

   Dear Mike,
   What do you say happens, if one uses a Windsor style thermostat ( no
   hat, full flow style as the true Robertshaw 330-180 ) and the OEM disc?
   I am sure this has come up in the past, but I need a refresher course.
   Please help,
   Bud #3400 ( Drive it like there is no tomorrow -- for there may not be
   ! )
   On Saturday, November 16, 2019, 10:04:00 PM CST, Mike Drew via DeTomaso
   <[2]detomaso at server.detomasolist.com> wrote:
   All,
   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.
   Here is a pic of a `real' Robertshaw 333-180 compared to the new one:
   Here is the new one with its included disc:
   And the disc laid over the thermostat:
   I'm sorry I don't have a stock disc handy to compare, and show the
   clearance between the orifice and the hat. You will just have to take
   my word for it....
   Mike (hoarding his one remaining good thermostat!)
   Sent from my iPad_______________________________________________
   Detomaso Email List is not managed by POCA
   Posted emails must not exceed 1.5 Megabytes
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   To manage your subscription (change email address, unsubscribe, etc.)
   use the links above.
   Members who post to this list grant license to the list to forward any
   message posted here to all past, current, or future members of the
   list. They also grant the list owner permission to maintain an archive
   or approve the archiving of list messages.

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References

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