Home » Public Forums » GMCnet » [GMCnet] 195 Degree Thermostat
| [GMCnet] 195 Degree Thermostat [message #333678] |
Mon, 18 June 2018 23:54  |
BobDunahugh
Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA
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GM called out the 195 degree thermostat for our GMC's. And about everything else back then. That's a great number for winter operation. Especially up North. Never have installed 160, or 180's. I now have the Benz fan that I can turn on at well. I've been turning the fan on about 5 miles prior to an off ramp that I plan to exit on. In an attempt to dump heat prior to the exit. So I'm wondering. With the 160 to 180's. Would this allow me to dump more heat prior to the exit ramp? Don't even want to think about the huge amount of variables on this one. Bob Dunahugh 78 Royale
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| Re: [GMCnet] 195 Degree Thermostat [message #333680 is a reply to message #333678] |
Tue, 19 June 2018 05:42  |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Bob,
I don't understand the logic behind nor necessity for your technique: If
you're cruising at 195*F, how will turning on the fan "dump heat"? The
thermostat should still hold the temperature at 195*F. Besides, when
cruising, the airflow should be sufficient that there would be little
increase from turning on the fan -- probably just bring it up to a
"neutral" speed rather than the "less than airflow" at which it would be
idling. And after the exit, the thermostat should still maintain the
195*F. If the temperature rose above that, then either you, or the
automatic control, should turn on the fan -- but only until the temperature
dropped back to 195*F. As for the 160*F to 180*F thermostats, certainly
they cause more heat to be rejected -- but WHY? It's well established that
engines operate more efficiently at the higher temperature; why sacrifice
that?
That's about how mine works, maintaining 196*-198*F always, even with my
old-fashioned thermostatic clutch.
Ken H.
On Tue, Jun 19, 2018 at 12:54 AM Bob Dunahugh wrote:
> GM called out the 195 degree thermostat for our GMC's. And about
> everything else back then. That's a great number for winter operation.
> Especially up North. Never have installed 160, or 180's. I now have the
> Benz fan that I can turn on at well. I've been turning the fan on about 5
> miles prior to an off ramp that I plan to exit on. In an attempt to dump
> heat prior to the exit. So I'm wondering. With the 160 to 180's. Would this
> allow me to dump more heat prior to the exit ramp? Don't even want to think
> about the huge amount of variables on this one. Bob Dunahugh 78 Royale
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] 195 Degree Thermostat [message #333681 is a reply to message #333680] |
Tue, 19 June 2018 06:09 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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G'day,
I made the mistake of installing a 160 degree thermostat in Double Trouble and on cold days at highway speeds the engine runs at
LESS than 160 degrees with an aluminum radiator and a standard fan.
I've never been able to figger that out!
In fact I NEVER hear the fan kick in at highway speeds, ram air does all the cooling.
Regards,
Rob M.
The Pedantic Mechanic
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808
-----Original Message-----
From: Gmclist [mailto:gmclist-bounces@list.gmcnet.org] On Behalf Of Ken Henderson
Sent: Tuesday, June 19, 2018 5:42 AM
To: GMC Mail List
Subject: Re: [GMCnet] 195 Degree Thermostat
Bob,
I don't understand the logic behind nor necessity for your technique: If
you're cruising at 195*F, how will turning on the fan "dump heat"? The
thermostat should still hold the temperature at 195*F. Besides, when
cruising, the airflow should be sufficient that there would be little
increase from turning on the fan -- probably just bring it up to a
"neutral" speed rather than the "less than airflow" at which it would be
idling. And after the exit, the thermostat should still maintain the
195*F. If the temperature rose above that, then either you, or the
automatic control, should turn on the fan -- but only until the temperature
dropped back to 195*F. As for the 160*F to 180*F thermostats, certainly
they cause more heat to be rejected -- but WHY? It's well established that
engines operate more efficiently at the higher temperature; why sacrifice
that?
That's about how mine works, maintaining 196*-198*F always, even with my
old-fashioned thermostatic clutch.
Ken H.
On Tue, Jun 19, 2018 at 12:54 AM Bob Dunahugh wrote:
> GM called out the 195 degree thermostat for our GMC's. And about
> everything else back then. That's a great number for winter operation.
> Especially up North. Never have installed 160, or 180's. I now have the
> Benz fan that I can turn on at well. I've been turning the fan on about 5
> miles prior to an off ramp that I plan to exit on. In an attempt to dump
> heat prior to the exit. So I'm wondering. With the 160 to 180's. Would this
> allow me to dump more heat prior to the exit ramp? Don't even want to think
> about the huge amount of variables on this one. Bob Dunahugh 78 Royale
>
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] 195 Degree Thermostat [message #333686 is a reply to message #333678] |
Tue, 19 June 2018 08:05 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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The thermostat has nothing to do with how hot your engine gets. It only controls how cold it gets. The capacity of the cooling system and fan on (engagement) point determines how hot it gets balanced against how much heat needs to be transfered and current conditions. So in theory with a 160 stat and forced manual fan engagement and non extreme conditions, you could possibly pull the temp down to 160 where the stat would begin throttling flow. That would he a bad thing and create unnecessary thermal cycling when 195 would be the target. With a 195 stat I don't think preemptive fan turn on when you hit the exit ramp is a bad idea at all. That transition from sustained road load to low speed is one of the more demanding situations due to multiple tough conditions-- engine road load heat still present, water pump speed drop, available fan drive RPM drop, and loss of forward motion air flow. In hot weather that is usually a point where the old style clutch engages as temp in air stream to clutch rises due to reduction of air speed. You can blow a wind tunnel force fan at the front end but with a 195 stat it should hold there. So like Ken said, if your cooling system is capable, the 5 min prior turn on seems unnecessary. But rather than waiting for your new fan setup to come on (not sure the stagger there) hitting it when you hit the ramp might even slow you down enough to not need brakes if timed just right.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] 195 Degree Thermostat [message #333693 is a reply to message #333691] |
Tue, 19 June 2018 11:17 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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Bob,
I understand what your trying to do.
You want less heat build up when you stop for gas.
Not a bad idea to do it as the fan will cool the fluid in the radiator and
that cooler fluid will weep into the block and help to lower the block temp.
I turn on the electric fan about the time i get off the ramp and leave it
on till i turn it off. Yes, the fan clutch being on will cool it below 195
as some of the coolent is designed to still move even when the thermostat
shuts off.
On Tue, Jun 19, 2018 at 8:58 AM, Bob Dunahugh wrote:
>
> I know the reasons for the 195. When I pull off the interstate for gas, or
> whatever. Shut the engine off. My Digi Panel alarm goes off due to heat
> buildup when I restart. I then turn the alarm off. Then sometimes forget to
> turn it back on for a while. That concerns me to not having the alarm
> active. Our 78 has the best radiator ducting. Radiator is clean inside, and
> out. Have the best water pump impeller.403 is clean inside, and out. As it
> has just 14,000 miles on it. YES. Not a real big deal. But I get anal
> about my 403. If they made a 190 degree. That just might do it. YES. I
> know I have personal problems in my head. ( GRIN ) Bob Dunahugh 78 Royale
>
> ________________________________
> From: Bob Dunahugh
> Sent: Monday, June 18, 2018 11:54 PM
> To: gmclist@list.gmcnet.org
> Subject: 195 Degree Thermostat
>
>
> GM called out the 195 degree thermostat for our GMC's. And about
> everything else back then. That's a great number for winter operation.
> Especially up North. Never have installed 160, or 180's. I now have the
> Benz fan that I can turn on at well. I've been turning the fan on about 5
> miles prior to an off ramp that I plan to exit on. In an attempt to dump
> heat prior to the exit. So I'm wondering. With the 160 to 180's. Would this
> allow me to dump more heat prior to the exit ramp? Don't even want to think
> about the huge amount of variables on this one. Bob Dunahugh 78 Royale
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Jim Kanomata
Applied/GMC, Newark,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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| Re: [GMCnet] 195 Degree Thermostat [message #333694 is a reply to message #333693] |
Tue, 19 June 2018 11:39 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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The 403 seems to be very pronounced to a sudden upward rush of heat
compared to the 455. My coach has always done it on sudden pull offs on the
freeway, fueling stops, etc. Don't know if it is particularly harmful,
been doing that for well over 100,000 miles. Through 4 fan clutches since I
have had it. I put the "shark gills" vents on the sides of the coach, and
the heat just pours out of them after a hot stop. Guess they work, too. No
digi panel to fret over, just stock cluster, plus a trans and final drive
gauge. The final drive is scary to watch in hot weather. Went a couple of
years before i ran wires to it. Ignorance is bliss.
Jim Hupy
On Tue, Jun 19, 2018, 9:18 AM Jim Kanomata wrote:
> Bob,
> I understand what your trying to do.
> You want less heat build up when you stop for gas.
> Not a bad idea to do it as the fan will cool the fluid in the radiator and
> that cooler fluid will weep into the block and help to lower the block
> temp.
> I turn on the electric fan about the time i get off the ramp and leave it
> on till i turn it off. Yes, the fan clutch being on will cool it below 195
> as some of the coolent is designed to still move even when the thermostat
> shuts off.
>
> On Tue, Jun 19, 2018 at 8:58 AM, Bob Dunahugh
> wrote:
>
>>
>> I know the reasons for the 195. When I pull off the interstate for gas,
> or
>> whatever. Shut the engine off. My Digi Panel alarm goes off due to heat
>> buildup when I restart. I then turn the alarm off. Then sometimes forget
> to
>> turn it back on for a while. That concerns me to not having the alarm
>> active. Our 78 has the best radiator ducting. Radiator is clean inside,
> and
>> out. Have the best water pump impeller.403 is clean inside, and out. As
> it
>> has just 14,000 miles on it. YES. Not a real big deal. But I get anal
>> about my 403. If they made a 190 degree. That just might do it. YES. I
>> know I have personal problems in my head. ( GRIN ) Bob Dunahugh 78 Royale
>>
>> ________________________________
>> From: Bob Dunahugh
>> Sent: Monday, June 18, 2018 11:54 PM
>> To: gmclist@list.gmcnet.org
>> Subject: 195 Degree Thermostat
>>
>>
>> GM called out the 195 degree thermostat for our GMC's. And about
>> everything else back then. That's a great number for winter operation.
>> Especially up North. Never have installed 160, or 180's. I now have the
>> Benz fan that I can turn on at well. I've been turning the fan on about
> 5
>> miles prior to an off ramp that I plan to exit on. In an attempt to dump
>> heat prior to the exit. So I'm wondering. With the 160 to 180's. Would
> this
>> allow me to dump more heat prior to the exit ramp? Don't even want to
> think
>> about the huge amount of variables on this one. Bob Dunahugh 78 Royale
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
>
>
>
> --
> Jim Kanomata
> Applied/GMC, Newark,CA
> jimk@appliedairfilters.com
> http://www.appliedgmc.com
> 1-800-752-7502
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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| Re: [GMCnet] 195 Degree Thermostat [message #333697 is a reply to message #333691] |
Tue, 19 June 2018 12:34 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Bob,
If the reason for the "Exit" is to stop, then I DO agree with your
procedure of turning on the fan -- and leaving it on for a while during the
stop (not overnight! :-) ) Continuing to blow heat out of the engine
compartment after the engine's shut down is certainly a good idea,
especially if, as many suggest, the 403 is especially prone to continued
temperature increase.
Back in my early days of motorhoming, I had a '76 Titan with a Chrysler 440
engine. We were doing OK all the way into the Texas Panhandle, but when I
slowed for the turn toward Palo Duro Canyon, the transmission downshifted
and there was an awful roar from under the hood. After a while, things
calmed down and we went on into the canyon and camped. That night I called
my friend who owned an RV dealership in NC, asking advice for my trip to
the transmission shop. He said, "Call my shop foreman in the morning." So
I did. HE had a big laugh: "That was the thermostatic fan coming on, NOT
the transmission down-shifting!" :-) First time I'd ever heard a
thermostatic fan, I guess.
He was right -- the next day I added a manual switch to the auxiliary
electric fan it already had. From then on, I did as you propose, Bob, and
never heard that ROAR again. :-)
Ken H.
On Tue, Jun 19, 2018 at 11:59 AM Bob Dunahugh wrote:
>
> I know the reasons for the 195. When I pull off the interstate for gas, or
> whatever. Shut the engine off. My Digi Panel alarm goes off due to heat
> buildup when I restart. I then turn the alarm off. Then sometimes forget to
> turn it back on for a while. That concerns me to not having the alarm
> active. Our 78 has the best radiator ducting. Radiator is clean inside, and
> out. Have the best water pump impeller.403 is clean inside, and out. As it
> has just 14,000 miles on it. YES. Not a real big deal. But I get anal
> about my 403. If they made a 190 degree. That just might do it. YES. I
> know I have personal problems in my head. ( GRIN ) Bob Dunahugh 78 Royale
> gmclist_list.gmcnet.org
>
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] 195 Degree Thermostat [message #333698 is a reply to message #333697] |
Tue, 19 June 2018 12:43 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Bob, just because you suspect that you have problems in your head, it does
not rule out that you do not have a mechanical problem to accompany them.
Someone once told me that "Just because you are paranoid, doesn't rule out
the fact that the whole world isn't out to get you". (Grin)
Jim Hupy
On Tue, Jun 19, 2018, 10:35 AM Ken Henderson wrote:
> Bob,
>
> If the reason for the "Exit" is to stop, then I DO agree with your
> procedure of turning on the fan -- and leaving it on for a while during the
> stop (not overnight! :-) ) Continuing to blow heat out of the engine
> compartment after the engine's shut down is certainly a good idea,
> especially if, as many suggest, the 403 is especially prone to continued
> temperature increase.
>
> Back in my early days of motorhoming, I had a '76 Titan with a Chrysler 440
> engine. We were doing OK all the way into the Texas Panhandle, but when I
> slowed for the turn toward Palo Duro Canyon, the transmission downshifted
> and there was an awful roar from under the hood. After a while, things
> calmed down and we went on into the canyon and camped. That night I called
> my friend who owned an RV dealership in NC, asking advice for my trip to
> the transmission shop. He said, "Call my shop foreman in the morning." So
> I did. HE had a big laugh: "That was the thermostatic fan coming on, NOT
> the transmission down-shifting!" :-) First time I'd ever heard a
> thermostatic fan, I guess.
>
> He was right -- the next day I added a manual switch to the auxiliary
> electric fan it already had. From then on, I did as you propose, Bob, and
> never heard that ROAR again. :-)
>
> Ken H.
>
>
>
> On Tue, Jun 19, 2018 at 11:59 AM Bob Dunahugh
> wrote:
>
>>
>> I know the reasons for the 195. When I pull off the interstate for gas,
> or
>> whatever. Shut the engine off. My Digi Panel alarm goes off due to heat
>> buildup when I restart. I then turn the alarm off. Then sometimes forget
> to
>> turn it back on for a while. That concerns me to not having the alarm
>> active. Our 78 has the best radiator ducting. Radiator is clean inside,
> and
>> out. Have the best water pump impeller.403 is clean inside, and out. As
> it
>> has just 14,000 miles on it. YES. Not a real big deal. But I get anal
>> about my 403. If they made a 190 degree. That just might do it. YES. I
>> know I have personal problems in my head. ( GRIN ) Bob Dunahugh 78 Royale
>> gmclist_list.gmcnet.org
>>
>>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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| Re: [GMCnet] 195 Degree Thermostat [message #333733 is a reply to message #333686] |
Tue, 19 June 2018 22:24 |
mrgmc3
Messages: 210
Registered: September 2013
Location: W Washington
Karma: 2
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Senior Member |
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JohnL455 wrote on Tue, 19 June 2018 08:05The thermostat has nothing to do with how hot your engine gets. It only controls how cold it gets. The capacity of the cooling system and fan on (engagement) point determines how hot it gets balanced against how much heat needs to be transfered and current conditions. So in theory with a 160 stat and forced manual fan engagement and non extreme conditions, you could possibly pull the temp down to 160 where the stat would begin throttling flow. That would he a bad thing and create unnecessary thermal cycling when 195 would be the target. With a 195 stat I don't think preemptive fan turn on when you hit the exit ramp is a bad idea at all. That transition from sustained road load to low speed is one of the more demanding situations due to multiple tough conditions-- engine road load heat still present, water pump speed drop, available fan drive RPM drop, and loss of forward motion air flow. In hot weather that is usually a point where the old style clutch engages as temp in air stream to clutch rises due to reduction of air speed. You can blow a wind tunnel force fan at the front end but with a 195 stat it should hold there....
I could not have said it better. I'm requoting to drive this point home as there seems to be major misconception about thermostats and cooling system function. The thermostat sets a "floor" temperature for operation. The radiator capacity, fin density, airflow and water pump flow determine the upper operating temp of the system. Another consideration when you are struggling with cooling efficiency is to verify the engine state of tune. Retarded spark and lean air fuel ratios can increase heat rejected to the coolant.
A final word on stats. 160F in cooler weather is too cold. The engine oil may not get hot enough to evaporate moisture or fuel from cold starts and blow by.
With all that said having the ability to manually force a fan on as you come off the freeway can't hurt.
Chris Geils - Twin Cities / W Wa
1978 26' Kingsley w/ very few mods; PD9040, aux trans cooler, one repaint in stock colors, R134a, Al rad, Alcoas, 54k mi
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