94 LT1 - Not All Thermostats are created equal
09-01-2012, 01:26 PM
#1
Drifting
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Location: 1994 LT1 Coupe 6-speed with FX3 & 2000 LS1 Vert 6-Speed with F45 Hunterdon County, NJ
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94 LT1 - Not All Thermostats are created equal
Hi all,
On my 94 Lt1 with 100k miles, while preparing for my final analysis before replacing the radiator (temps not bad, 194-197 but creeping up to 205-10 while driving which it did not used to do), decided to replace the 5 year-old AC Delco thermostat (131-100).
In doing research on which brand/model to install, I discovered two of the main manufactures now have a 'cheap' and 'decent' model (AC Delco has their regular one - 131-100 & their 'Professional' model - 12TH10D --and-- Stant has a regular and a 'Super-Stat' model - 45218).
The interesting physical difference between the AC Delco 'regular' 131-100 and Stant 'Super-Stat' 45218 is the size of the 'heat engine' (wax within copper moving device) --AND-- the Stant 'Super-Stat' has a 'jiggler' to allows air to bleed upward through the thermostat when closed). So for a couple dollars more, it eliminates the need to do what most folks do -- drill a hole through the thermostat to faciliate air bleeding.
The more interesting operational difference is the speed of opening.
Albeit both opened and closed at about the same temperature and opened about the same amount (1/4"), The Stant 'Super-Stat' opens noticeably more slowly as well as closing more slowly.
I believe this is a desireable improvement, especially based on the reverse flow of the LT1 (i.e. cooled radiator coolant enters the engine through the thermosat vs the earlier L98 engines where hot engine coolant exits the engine through the thermostat).
By the thermostat moving more slowly, as the cooler water from the radiator is introduced into the water-pump, it will NOT suddenly close and restict inflow, but remain open longer, thereby accepting more coolant from the radiator, likely resulting in better mixing of the radiator coolant with the engine coolant, possibly further reduce hot-spots within the engine and improving the flow through the radiator, which might keep the temperatures lower too.
AFTER NEW RADIATOR INSTALLATION UPDATE -- SLOWER IS NOT BETTER -- TEMPERATURE SWING TOO MUCH DUE TO SLOW THERMOSTAT -- ON TEST DRIVE ROSE TO 205 and DIPPED TO 186... GOING TO TRY BETTER AC DELCO OR RETURN TO ORIGINAL AC DELCO.
Note intial tests in garage show the Stant 'Super-Stat' has the same digital temperature points as the old thermostat (slow rise to 194, then pause, then to 196-197 next pause), was not using a fan in front of the car this time.
Will do a test drive this afternoon and post back results.
FYI, Whereas the AC Delco was 5 yrs old, very little mileage on it as car was effectively not driven over the past 3 years, so I believe it still operated similiar to when it was new.
So likely moral -- spend a couple dollars more and purchase the better model of thermostat, no matter the brand, likely worth it...
On my 94 Lt1 with 100k miles, while preparing for my final analysis before replacing the radiator (temps not bad, 194-197 but creeping up to 205-10 while driving which it did not used to do), decided to replace the 5 year-old AC Delco thermostat (131-100).
In doing research on which brand/model to install, I discovered two of the main manufactures now have a 'cheap' and 'decent' model (AC Delco has their regular one - 131-100 & their 'Professional' model - 12TH10D --and-- Stant has a regular and a 'Super-Stat' model - 45218).
The interesting physical difference between the AC Delco 'regular' 131-100 and Stant 'Super-Stat' 45218 is the size of the 'heat engine' (wax within copper moving device) --AND-- the Stant 'Super-Stat' has a 'jiggler' to allows air to bleed upward through the thermostat when closed). So for a couple dollars more, it eliminates the need to do what most folks do -- drill a hole through the thermostat to faciliate air bleeding.
The more interesting operational difference is the speed of opening.
Albeit both opened and closed at about the same temperature and opened about the same amount (1/4"), The Stant 'Super-Stat' opens noticeably more slowly as well as closing more slowly.
I believe this is a desireable improvement, especially based on the reverse flow of the LT1 (i.e. cooled radiator coolant enters the engine through the thermosat vs the earlier L98 engines where hot engine coolant exits the engine through the thermostat).
By the thermostat moving more slowly, as the cooler water from the radiator is introduced into the water-pump, it will NOT suddenly close and restict inflow, but remain open longer, thereby accepting more coolant from the radiator, likely resulting in better mixing of the radiator coolant with the engine coolant, possibly further reduce hot-spots within the engine and improving the flow through the radiator, which might keep the temperatures lower too.
AFTER NEW RADIATOR INSTALLATION UPDATE -- SLOWER IS NOT BETTER -- TEMPERATURE SWING TOO MUCH DUE TO SLOW THERMOSTAT -- ON TEST DRIVE ROSE TO 205 and DIPPED TO 186... GOING TO TRY BETTER AC DELCO OR RETURN TO ORIGINAL AC DELCO.
Note intial tests in garage show the Stant 'Super-Stat' has the same digital temperature points as the old thermostat (slow rise to 194, then pause, then to 196-197 next pause), was not using a fan in front of the car this time.
Will do a test drive this afternoon and post back results.
FYI, Whereas the AC Delco was 5 yrs old, very little mileage on it as car was effectively not driven over the past 3 years, so I believe it still operated similiar to when it was new.
So likely moral -- spend a couple dollars more and purchase the better model of thermostat, no matter the brand, likely worth it...
Last edited by theadmiral94; 09-09-2012 at 08:04 PM. Reason: correction slower response is NOT better
09-01-2012, 03:21 PM
#3
Instructor
I recently replaced the thermostat in my 1994 with the stant super stat as well. I figured I would pay a few extra bucks for the premium model. The car operates at the exact temperatures the OP mentioned while driving around.
The car still has the original radiator and 130k miles. I thought it was interesting how it pauses at 194. Is that when the thermostat is completely open?
slow rise to 194, then pause, then to 196-197 next pause
09-01-2012, 04:55 PM
#4
Drifting
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Stant Super-Stat seems to reduce temp flucuations
Hi All,
driving test complete. Albeit temps slightly higher than normal (outside temp hot too, 93-96 per AC Head), likley the system still needs another 'burp', especially given I have yet to put back in all the anti-freeze I took out (reused fluid as was nice and green and very little mileage).
So, good news is the 'Super-Stat' seems to slow down the swings of the temperature, and slower changes to the temperature is better for the engine.
On 45 min drive, temperature climbed to 194, paused a bit (shorter than than when idle-ing in the garage), and then went to 196-197, but then did rise and fall from there to 215 (A/C was off) depending on speed, rpms, etc.
I would say this is an improvement over the smaller 'heat engine' in the low-grade AC Delco unit, and presume this welcomed slower response would also occur with the higher-grade AC Delco and other brands too.
To CNJ Surveyor,
To answer your question, the pause at 194 is likely when the 180F degree thermostat starts to open and the temperature which IF the radiator was properly sized, would be the temperature all the time. To support this assumption, note the FSM 'test' which says to raise the temperature of the immersion fluid to 20F degrees above the thermostat's temperature, so given the fluid travel distance between the thermostat's location in the top of the waterpump housing, and the position of the digital temperature sensor, the 15F degree difference makes perfect sense to me.
Also, my stove top testing did show the Stant 'Super-Stat' thermostat starting to open at 180F degrees, but didn't test the old AC Delco one for a slow temp rise from below 180F degrees.
driving test complete. Albeit temps slightly higher than normal (outside temp hot too, 93-96 per AC Head), likley the system still needs another 'burp', especially given I have yet to put back in all the anti-freeze I took out (reused fluid as was nice and green and very little mileage).
So, good news is the 'Super-Stat' seems to slow down the swings of the temperature, and slower changes to the temperature is better for the engine.
On 45 min drive, temperature climbed to 194, paused a bit (shorter than than when idle-ing in the garage), and then went to 196-197, but then did rise and fall from there to 215 (A/C was off) depending on speed, rpms, etc.
I would say this is an improvement over the smaller 'heat engine' in the low-grade AC Delco unit, and presume this welcomed slower response would also occur with the higher-grade AC Delco and other brands too.
To CNJ Surveyor,
To answer your question, the pause at 194 is likely when the 180F degree thermostat starts to open and the temperature which IF the radiator was properly sized, would be the temperature all the time. To support this assumption, note the FSM 'test' which says to raise the temperature of the immersion fluid to 20F degrees above the thermostat's temperature, so given the fluid travel distance between the thermostat's location in the top of the waterpump housing, and the position of the digital temperature sensor, the 15F degree difference makes perfect sense to me.
Also, my stove top testing did show the Stant 'Super-Stat' thermostat starting to open at 180F degrees, but didn't test the old AC Delco one for a slow temp rise from below 180F degrees.
09-09-2012, 08:01 PM
#6
Drifting
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Member Since: Sep 2003
Location: 1994 LT1 Coupe 6-speed with FX3 & 2000 LS1 Vert 6-Speed with F45 Hunterdon County, NJ
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Slow thermostat is not better
Hi All,
I Put in a new radiator (Delphi RA 1138) and did a major cleaning of the AC Condenser). Now, the radiator can cool the engine below the thermostat setting (yea!).
However, I discovered that the Stant Super-Stat's slow-response IS NOT an advantage and plan on changing back to AC Delco, either original one or their 'professional' version.
During my 30 mile 1 hour test drive, whereas the temperature now stays much lower than before (196-205 versus 200-220 thanks to the new radiator),
The Stant Super-Stat thermostat DOES NOT not keep the temperature as steady as the old AC Delco thermostat used to (e.g. while driving at 55 mph, temp now varies from 190 through 201 -- versus it used to stay pretty steady at 194).
So unfortunately, even though the 'jiggler' did make filling and bleeding much easier, I must withdraw my recommendation of the Stant Super-Stat based on my latest results.
I Put in a new radiator (Delphi RA 1138) and did a major cleaning of the AC Condenser). Now, the radiator can cool the engine below the thermostat setting (yea!).
However, I discovered that the Stant Super-Stat's slow-response IS NOT an advantage and plan on changing back to AC Delco, either original one or their 'professional' version.
During my 30 mile 1 hour test drive, whereas the temperature now stays much lower than before (196-205 versus 200-220 thanks to the new radiator),
The Stant Super-Stat thermostat DOES NOT not keep the temperature as steady as the old AC Delco thermostat used to (e.g. while driving at 55 mph, temp now varies from 190 through 201 -- versus it used to stay pretty steady at 194).
So unfortunately, even though the 'jiggler' did make filling and bleeding much easier, I must withdraw my recommendation of the Stant Super-Stat based on my latest results.
