[DeTomaso] Interesting Robertshaw 333-180 thermostat design change
Mike Drew
MikeLDrew at aol.com
Sun Nov 17 01:04:32 EST 2019
Bud,
Another great question. Here is a Garth Rodericks pic of the relevant area of the block, looking down from above:
You can clearly see the disc which is partially blocked by the thermostat hat. The hole where the temp sender goes is at lower left, facing forward.
There is a cavity about an inch tall inside the block. Water fills this cavity and touches the temp sender at all times, so it always reads current ENGINE water temp (which closely mirrors the actual engine temp, assuming no air in the system). When the engine is cold, the thermostat is closed, the hole in the disc is uncovered, the water pipe above the thermostat is blocked off by the thermostat, and the water passes through the hole to circulate through the engine.
When the thermostat (which faces upwards) is heated by the warming water, it opens, which does two things. It partially blocks the hole in the disc, and allows the water to flow upwards through the pipe and back to the top of the pressure bottle/swirl tank. Water then flows out the bottom of that tank, forward to the radiator, where it is cooled, then sucked rearwards by the water pump. There it is pressurized and forced into and through the engine, flowing from bottom to top, eventually winding up back where we started and the cycle repeats.
Mike
Sent from my iPad
> On Nov 16, 2019, at 21:46, B Hower <b.hower3400 at yahoo.com> wrote:
>
> Dear Mike,
>
> Thank you very much, that helps me a lot. So then with OEM set up ( thermostat and disc ) and temperature sensor mounted at the front of the block, near thermostat, does the sensor see water that is flowing through the radiator or water circulating around and around in the engine? And does that change depending on thermostat open or closed position?
>
> Thanks, I need more schooling,
>
> Bud #3400 ( Drive it like there is no tomorrow -- for there may not be ! )
>
>
> On Saturday, November 16, 2019, 11:20:00 PM CST, Mike Drew <mikeldrew at aol.com> wrote:
>
>
> 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_______________________________________________
>>
>>
>> Detomaso Email List is not managed by POCA
>> Posted emails must not exceed 1.5 Megabytes
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>>
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>> <image1.jpeg>
>> <image2.jpeg>
>> <image3.jpeg>
-------------- next part --------------
Bud,
Another great question. Here is a Garth Rodericks pic of the relevant
area of the block, looking down from above:
image1.jpeg
You can clearly see the disc which is partially blocked by the
thermostat hat. The hole where the temp sender goes is at lower left,
facing forward.
There is a cavity about an inch tall inside the block. Water fills this
cavity and touches the temp sender at all times, so it always reads
current ENGINE water temp (which closely mirrors the actual engine
temp, assuming no air in the system). When the engine is cold, the
thermostat is closed, the hole in the disc is uncovered, the water pipe
above the thermostat is blocked off by the thermostat, and the water
passes through the hole to circulate through the engine.
When the thermostat (which faces upwards) is heated by the warming
water, it opens, which does two things. It partially blocks the hole in
the disc, and allows the water to flow upwards through the pipe and
back to the top of the pressure bottle/swirl tank. Water then flows
out the bottom of that tank, forward to the radiator, where it is
cooled, then sucked rearwards by the water pump. There it is
pressurized and forced into and through the engine, flowing from bottom
to top, eventually winding up back where we started and the cycle
repeats.
Mike
Sent from my iPad
On Nov 16, 2019, at 21:46, B Hower <[1]b.hower3400 at yahoo.com> wrote:
Dear Mike,
Thank you very much, that helps me a lot. So then with OEM set up (
thermostat and disc ) and temperature sensor mounted at the front of
the block, near thermostat, does the sensor see water that is flowing
through the radiator or water circulating around and around in the
engine? And does that change depending on thermostat open or closed
position?
Thanks, I need more schooling,
Bud #3400 ( Drive it like there is no tomorrow -- for there may not be
! )
On Saturday, November 16, 2019, 11:20:00 PM CST, Mike Drew
<[2]mikeldrew at aol.com> wrote:
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 <[3]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
<[4]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
DeTomaso mailing list
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use the links above.
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list. They also grant the list owner permission to maintain an archive
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References
1. mailto:b.hower3400 at yahoo.com
2. mailto:mikeldrew at aol.com
3. mailto:b.hower3400 at yahoo.com
4. mailto:detomaso at server.detomasolist.com
5. mailto:DeTomaso at server.detomasolist.com
6. http://server.detomasolist.com/mailman/listinfo/detomaso
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