RobertShaw Thermostats
Thread Starter
Instructor
Joined: Aug 2006
Posts: 247
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RobertShaw Thermostats
Hi!
I have heard stories that RobertShaw Thermostats (either the 160 or the 180 degrees models) have, by themselves, lowered overall operating temperatures substantially over stock 195 thermostats or the standard 160/180 models that you usually see in auto parts stores. Without getting into a big physics discourse about whether this really can be true, can anyone out there confirm this through experience?
Thanks,
/s/ Chris Kennedy
I have heard stories that RobertShaw Thermostats (either the 160 or the 180 degrees models) have, by themselves, lowered overall operating temperatures substantially over stock 195 thermostats or the standard 160/180 models that you usually see in auto parts stores. Without getting into a big physics discourse about whether this really can be true, can anyone out there confirm this through experience?
Thanks,
/s/ Chris Kennedy
Drifting
Joined: Feb 2003
Posts: 1,614
Likes: 163
From: Davis CA
I think that the best of many responses to this question was offered by CentralCoaster with graphs. The bottomline is that it won't change the ability of your system to remove heat. It will change the point where the process begins. Driving in cool weather, you will probably stay in the 180s. Idling in stopped traffic, you will still reach 230 or whatever the temperature is at which your fans are programmed to engage.
Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
I started a thread after reading comments about the differences
in performance between different styles of thermostats.
Engine Thermostats - Robertshaw & Reverse Poppet style
My initial results demonstrated that the Robertshaw style units were
opening EARLIER than their rated temperature while the poppet style
were opening AT or after their rated temps.
Under these circumstances effectiveness becomes a matter of
perception and duplicitous marketing. If there is a 195º stat in the
engine but it is actually opening at 180º, of course the engine runs
cooler. However, compare a poppet and a Robertshaw that both
truly actuate at the same temperature and my vote is there will be
very little difference in cooling effectiveness that can be attributed
to the design of the thermostat.
I intended to do some further testing. I collected more samples of
thermostats from different vendors and with different operating temps
but have not made time at the stove yet.
.
in performance between different styles of thermostats.
Engine Thermostats - Robertshaw & Reverse Poppet style
My initial results demonstrated that the Robertshaw style units were
opening EARLIER than their rated temperature while the poppet style
were opening AT or after their rated temps.
Under these circumstances effectiveness becomes a matter of
perception and duplicitous marketing. If there is a 195º stat in the
engine but it is actually opening at 180º, of course the engine runs
cooler. However, compare a poppet and a Robertshaw that both
truly actuate at the same temperature and my vote is there will be
very little difference in cooling effectiveness that can be attributed
to the design of the thermostat.
I intended to do some further testing. I collected more samples of
thermostats from different vendors and with different operating temps
but have not made time at the stove yet.
.
Le Mans Master
Joined: Jun 2006
Posts: 5,642
Likes: 5
From: One day you're a Comet...the next day you're dust... Arkansas
Hi!
I have heard stories that RobertShaw Thermostats (either the 160 or the 180 degrees models) have, by themselves, lowered overall operating temperatures substantially over stock 195 thermostats or the standard 160/180 models that you usually see in auto parts stores. Without getting into a big physics discourse about whether this really can be true, can anyone out there confirm this through experience?
Thanks,
/s/ Chris Kennedy
I have heard stories that RobertShaw Thermostats (either the 160 or the 180 degrees models) have, by themselves, lowered overall operating temperatures substantially over stock 195 thermostats or the standard 160/180 models that you usually see in auto parts stores. Without getting into a big physics discourse about whether this really can be true, can anyone out there confirm this through experience?
Thanks,
/s/ Chris Kennedy
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Even if they start to crack open at the exact same time, the robertshaw is already way more open due to the design, so it'll probably run a few degrees cooler at those temps.
But it's insignificant. The Robertshaw is supposed to be balanced, and less likely to close up at high rpms.
I pulled mine out because it quit working properly, the car acted like it wasn't opening fully. I haven't tested it yet to see what the problem is.
But it's insignificant. The Robertshaw is supposed to be balanced, and less likely to close up at high rpms.
I pulled mine out because it quit working properly, the car acted like it wasn't opening fully. I haven't tested it yet to see what the problem is.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Think about what a thermostat does. It can only set a minimum operating temperature. It does not control or affect a maximum temp. If your operating temps are above 195°, with a 195° stat, a stat that opens sooner will have no effect, except delay getting TO 195°.
RACE ON!!!
RACE ON!!!
Melting Slicks
Joined: Apr 2007
Posts: 2,678
Likes: 1
From: Atlanta Georgia
hey everyone, i was interested in the whole thermastat thing. i saw in a few peoples signatures on other sites that they had 180 degree thermostat or whatever and didnt understand what it did. so to refresh my memory it seems like it just turns ur fan on earlier than it would on a stock thermo? and it sounds like it really isnt worth it from things people have said, is this true?
thanks
jason
thanks
jason
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Thread Starter
Instructor
Joined: Aug 2006
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Think about what a thermostat does. It can only set a minimum operating temperature. It does not control or affect a maximum temp. If your operating temps are above 195°, with a 195° stat, a stat that opens sooner will have no effect, except delay getting TO 195°.
RACE ON!!!
RACE ON!!!
Cheers,
/s/ Chris
Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
If cooling capacity and or environmental conditions are such that BTU's
generated by the engine are less than can be transfered by the system
then the operating temperature will be determined by the value the
thermostat actually opens at.
On a 40-50ºF evening at a highway cruise speed, a failing thermostat
that will not close causes the engine to run below the 195º that it
used to attain. This problem becomes more acute when temperatures
are in the vicinity of -40ºF (plus windchill)
.
Drifting
Joined: Oct 2006
Posts: 1,328
Likes: 14
From: Stafford Connecticut
I put a robert shaw 180 degree thermostat in my 85 vette and I like the lower temps. My vette used to run at 200 degrees now runs at 175 180 I like that much better.I don't know the physics just know my vette runs cooler
Thread Starter
Instructor
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/s/ Chris Kennedy
Team Owner
Joined: May 2002
Posts: 24,337
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Chris, it's quite simple really.
The thermostat tries to keep your engine above the thermostat rating temp. The fans try to keep your engine below the fan switch temp. That is all they do, nothing else.
When your engine is warmed up, it will always be within this temperature range.
Read here:
http://forums.corvetteforum.com/show...16&forum_id=48
And refer to this chart. A lower temp thermostat will cause the engine to run cooler ONLY when you don't need it. It will not effect the temps on a hot summer day, or at hot idle.
The thermostat tries to keep your engine above the thermostat rating temp. The fans try to keep your engine below the fan switch temp. That is all they do, nothing else.
When your engine is warmed up, it will always be within this temperature range.
Read here:
http://forums.corvetteforum.com/show...16&forum_id=48
And refer to this chart. A lower temp thermostat will cause the engine to run cooler ONLY when you don't need it. It will not effect the temps on a hot summer day, or at hot idle.
Safety Car
Joined: Apr 2001
Posts: 3,525
Likes: 2
From: Houston TX
But wait...
What about the fact that fully open, the Robertshaw t-stats have more flow area than a popet-type t-stat (feel free, I did this many years ago, and the difference is fairly significant)? More flow equals more heat transfer fluid circulating. Assuming a delta between the heat transfer fluid waiting to enter the engine (radiator side) and the engine temp would ensure that the the greater flow would equal lower engine operating temps. This is all true assuming equivalent heat transfer coefficients of the fluid, the surfaces, and equal introduction point of the heat transfer fluid (points at which the t-stat opens).
But wait, I am getting off into my old ChE days which may not be allowed.
Aaron
What about the fact that fully open, the Robertshaw t-stats have more flow area than a popet-type t-stat (feel free, I did this many years ago, and the difference is fairly significant)? More flow equals more heat transfer fluid circulating. Assuming a delta between the heat transfer fluid waiting to enter the engine (radiator side) and the engine temp would ensure that the the greater flow would equal lower engine operating temps. This is all true assuming equivalent heat transfer coefficients of the fluid, the surfaces, and equal introduction point of the heat transfer fluid (points at which the t-stat opens).
But wait, I am getting off into my old ChE days which may not be allowed.
Aaron
Team Owner
Joined: May 2002
Posts: 24,337
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Yeah increasing flow will increase your LMTD and heat transfer proportionally, but I expect it will be pretty marginal when you consider the pressure losses through the rest of the system.
Thread Starter
Instructor
Joined: Aug 2006
Posts: 247
Likes: 0
Chris, it's quite simple really.
The thermostat tries to keep your engine above the thermostat rating temp. The fans try to keep your engine below the fan switch temp. That is all they do, nothing else.
When your engine is warmed up, it will always be within this temperature range.
Read here:
http://forums.corvetteforum.com/show...16&forum_id=48
And refer to this chart. A lower temp thermostat will cause the engine to run cooler ONLY when you don't need it. It will not effect the temps on a hot summer day, or at hot idle.
The thermostat tries to keep your engine above the thermostat rating temp. The fans try to keep your engine below the fan switch temp. That is all they do, nothing else.
When your engine is warmed up, it will always be within this temperature range.
Read here:
http://forums.corvetteforum.com/show...16&forum_id=48
And refer to this chart. A lower temp thermostat will cause the engine to run cooler ONLY when you don't need it. It will not effect the temps on a hot summer day, or at hot idle.
Cheers,
/s/ Chris
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Maybe it was the fresh mix of coolant and more air was burped out than previously.
Why would you want to work in San Diego? That's like taking a pay cut. You could manage a gas station in Kansas and still have more left over there for cars, house, kids, etc.
Why would you want to work in San Diego? That's like taking a pay cut. You could manage a gas station in Kansas and still have more left over there for cars, house, kids, etc.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by Chris Kennedy
I understand what you mean, but with another Corvette I had the experience that if you could start the cooling/open thermostat process earlier, the car very seldom reached the same temperatures as before. In other words, a fully flowing/cooling system at 180 degrees may be able to keep it there, but if you start the full flow/cooling at 195 degrees, then the same system won't be able to get the temperature back down to 180 degrees even if you could somehow prevent the 195 degree thermostat from closing.
RACE ON!!!
Race Director
Joined: Jun 2004
Posts: 13,963
Likes: 709
From: WI
Is the Robert Shaw 'stat drilled? I thought that was the one that had three holes drilled in it. You'll notice some differences with that many holes.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by Slalom4me
Quote:
There is a caveat to this truism.
If cooling capacity and or environmental conditions are such that BTU's
generated by the engine are less than can be transfered by the system
then the operating temperature will be determined by the value the
thermostat actually opens at.
On a 40-50ºF evening at a highway cruise speed, a failing thermostat
that will not close causes the engine to run below the 195º that it
used to attain. This problem becomes more acute when temperatures
are in the vicinity of -40ºF (plus windchill)
Originally Posted by CFI-EFI
If your operating temps are above 195°, with a 195° stat, a stat that opens
sooner will have no effect, except delay getting TO 195°.
sooner will have no effect, except delay getting TO 195°.
There is a caveat to this truism.
If cooling capacity and or environmental conditions are such that BTU's
generated by the engine are less than can be transfered by the system
then the operating temperature will be determined by the value the
thermostat actually opens at.
On a 40-50ºF evening at a highway cruise speed, a failing thermostat
that will not close causes the engine to run below the 195º that it
used to attain. This problem becomes more acute when temperatures
are in the vicinity of -40ºF (plus windchill)
"If your operating temps are above 195°, with a 195° stat, a stat that opens sooner will have no effect, except delay getting TO 195°."
No caveats, conditions, qualifying phrases, nor silly suppositions about failing thermostats and/or -40° weather are either applicable or germane.
RACE ON!!!