Home » Public Forums » GMCnet » What T Stat for EFI
| What T Stat for EFI [message #242154] |
Mon, 03 March 2014 10:13  |
Oldngray
Messages: 544
Registered: August 2009
Location: Punta Gorda Florida
Karma: 0
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Does it make a difference what T Stat to use on the 455 with EFI/EBL.
Current is 180 and I think it is failing, was going to use another 180 but was told the EFI needs a hotter (195) to get out of closed loop.
Do not know what that means.
Thanks
Richard MacDonald
Punta Gorda, Florida
Sold our TZE April 2015
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| Re: [GMCnet] What T Stat for EFI [message #242156 is a reply to message #242154] |
Mon, 03 March 2014 10:30  |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Richard, I think the temp sensor reaches high limit at 173 degrees or close
to that. Open/closed loop is largely a product of exhaust O2 sensor, but is
influenced by the upper limit on the temp sensor. If you are at 180 or
above, and the temp sensor is working as it should, the 180 thermostat
should be fine. If you want more heat from your heater, use the 195 in
winter, and 180 in summer. Open loop can be compared to an open circuit in
electricity. No current can flow. When in closed loop, data can flow in
that 02 circuit, and the computer can vary the pulse width on the injectors
to match the 02 present in the exhaust gasses.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Mon, Mar 3, 2014 at 8:13 AM, Richard MacDonald <rm1936@gmail.com> wrote:
>
>
> Does it make a difference what T Stat to use on the 455 with EFI/EBL.
> Current is 180 and I think it is failing, was going to use another 180 but
> was told the EFI needs a hotter (195) to get out of closed loop.
>
> Do not know what that means.
> Thanks
> --
> Richard MacDonald
> Punta Gorda, Florida
> 76 Edgemonte TZE 266V102313
> Howell TBI EBL
>
>
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| Re: What T Stat for EFI [message #242158 is a reply to message #242154] |
Mon, 03 March 2014 10:43 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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I have no idea what EFI you are using, but I have a scangage on my Chevy Colorado and it goes into closed loop at around 105 to 110 degrees F. It also comes for the factory with a 180 thermostat.
In the winter time that aluminum engine has a hard time maintaining 180. It usually runs 170 to 174 when the OAT is below +10. I replaced the thermostat and the new one does the same thing. I posted a question on the Colorado forum and found that others are seeing the same numbers. In the summer it runs 178 to 182. I never get any messages about low temperature with those numbers.
I know nothing about EFI but I thought the closed loop operation was determined by the oxygen sensor, coolant temp over 100, and some period of time.
If you are running around 180, I would look somewhere other than coolant temperature for your problem. Where is the temperature sensor for the EFI mounted and is it OK? How is the oxygen sensor?
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: What T Stat for EFI [message #242166 is a reply to message #242158] |
Mon, 03 March 2014 11:35 |
Oldngray
Messages: 544
Registered: August 2009
Location: Punta Gorda Florida
Karma: 0
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Thanks Jim and Ken for the replys, I have the Howell, and will go with the 180 again.
Richard MacDonald
Punta Gorda, Florida
Sold our TZE April 2015
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| Re: What T Stat for EFI [message #242172 is a reply to message #242154] |
Mon, 03 March 2014 12:04 |
cbryan
Messages: 451
Registered: May 2012
Location: Ennis, Texas
Karma: 3
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In my Accel multiport setup with the 500 Cadillac, the literature has a cryptic reference: "Use a 180 degree thermostat". Doing some research I find that some Ford drag racers like 160 degrees for maximum power. Accel has its roots in racing. There may be another reason.
However, in an old old flathead hotrod book showing a curve for cylinder wear as a function of coolant temperature, it is rapid for less than 160 degrees, going down smoothly with increased coolant temperature. Very low for 180 degrees, but looks about 30% lower still for 195. Saving 30% wear? Sign me up. I remember this because it is counter to my first belief, which was "cooler is better, 100% of the time."
Drag racers do not worry about long term wear of cylinder walls.
On the internet, people observe straight six engines where the front cylinder is almost always worn most, presumably because that cylinder gets the return coolant first, therefore runs cooler.
Some take the trouble to plumb the coolant return direct to the heads near the exhaust valves. A plumber's nightmare. Makes a lot of sense.
Dan runs a 195 thermostat in winter and a 180 in summer. Better heater output, I think. I like cardboard "radiator shutters" for cold weather. High tech redneck.
What I have written is far more than I know. Trying to understand.
HTH.
Carey
Carey from Ennis, Texas
78 Royale, 500 Cadillac, Rance Baxter EFI.
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| Re: What T Stat for EFI [message #242187 is a reply to message #242158] |
Mon, 03 March 2014 14:35 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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I found this statement here:
http://www.thirdgen.org/open-loop-closed-loop
The system will stay in 'Open Loop' until the following conditions are met:
1. The O2 sensor has varying voltage output, showing that it is hot enough to operate properly. (This depends on temperature)
2. The coolant sensor is above a specified temperature about 40oC/104oF.
3. A specific amount of time has elapsed after starting the engine.
I also found this:
http://www.hotrodhandbooks.com.au/eBooks/TPI/TPI%20On%20Line-03-2.html
Open Loop
When the engine is first started the system goes into open loop operation. In open loop, the ECM calculates the Air/Fuel ratio based on inputs from the coolant and MAF sensors. The system remains in open-loop until the following three conditions are met:
Coolant temperature above 105°F.
Oxygen sensor has varying output voltage (indicating it is hot enough to operate properly).
A specific amount of time (preprogrammed into the MEM-CAL) has elapsed.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: What T Stat for EFI [message #242202 is a reply to message #242172] |
Mon, 03 March 2014 16:22 |
mikethebike
Messages: 331
Registered: January 2014
Karma: 0
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I think that old flatty with rapid wear below 160 had a lot to do with the oil back then. I'll wager that with modern oil the wear at 140 or 150 is negligible.
But to address closed vs open loop....open loop has a predetermined fuel map (Harley-Davidson) and requires remapping when enough changes like cams, headers, throttle bodies etc are done to the engine are made whereas closed loop with an o2 sensor does not require a remap due to the fact that the system continually 'maps' the fuel curve based on tps, air/water temp, barometric pressure, vacuum and o2 feedback. My Z/28 had 3 o2 sensors and I've heard that some high dollar cars have 1 per cylinder. You might need to increase the injector flow rate to more lbs per hour to keep up.
| cbryan wrote on Mon, 03 March 2014 12:04 |
In my Accel multiport setup with the 500 Cadillac, the literature has a cryptic reference: "Use a 180 degree thermostat". Doing some research I find that some Ford drag racers like 160 degrees for maximum power. Accel has its roots in racing. There may be another reason.
However, in an old old flathead hotrod book showing a curve for cylinder wear as a function of coolant temperature, it is rapid for less than 160 degrees, going down smoothly with increased coolant temperature. Very low for 180 degrees, but looks about 30% lower still for 195. Saving 30% wear? Sign me up. I remember this because it is counter to my first belief, which was "cooler is better, 100% of the time."
Drag racers do not worry about long term wear of cylinder walls.
On the internet, people observe straight six engines where the front cylinder is almost always worn most, presumably because that cylinder gets the return coolant first, therefore runs cooler.
Some take the trouble to plumb the coolant return direct to the heads near the exhaust valves. A plumber's nightmare. Makes a lot of sense.
Dan runs a 195 thermostat in winter and a 180 in summer. Better heater output, I think. I like cardboard "radiator shutters" for cold weather. High tech redneck.
What I have written is far more than I know. Trying to understand.
HTH.
Carey
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[Updated on: Mon, 03 March 2014 16:50] Report message to a moderator |
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| Re: What T Stat for EFI [message #242209 is a reply to message #242154] |
Mon, 03 March 2014 17:22 |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
Karma: 11
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| Oldngray wrote on Mon, 03 March 2014 08:13 |
Does it make a difference what T Stat to use on the 455 with EFI/EBL.
Current is 180 and I think it is failing, was going to use another 180 but was told the EFI needs a hotter (195) to get out of closed loop.
Do not know what that means.
Thanks
|
This one is sort of a matter of personal preference. Some like to idle in open loop. Because EBL allows us to change some of these parameters, I set my temperature threshold fairly low, probably like Ken's truck. I do this because I like the idea of the O2 sensor telling the computer how things are going. This means you can get out of closed loop when you choose regardless of the thermostat. Because it is closed until 180... regardless of 180 or 195 units, the higher thermostat only makes a difference above 180.
As mentioned in this thread, temperature is not the only parameter required for the system to go into closed loop. Many of us have found that an unheated O2 sensor has a hard time making the computer be happy at idle, let alone warmup. So, a working, heated, O2 sensor will probably) get you out of closed loop quicker, along with lowering the temperature threshold.
I have an aluminum intake which has the exhaust blocked off, making it a little harder to "warm up" than a stock setup. I notice that my idle evens out considerably when the computer/TBI quits guessing and starts squirting gas in an informed way.
I have been running a 195 for a year or two, thinking it might help vaporize gas, especially in the aluminum intake. To tell the truth, I notice no real difference when compared to the 180 I used for years... with EFI.
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
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| Re: What T Stat for EFI [message #242243 is a reply to message #242154] |
Mon, 03 March 2014 23:16 |
mrgmc3
Messages: 210
Registered: September 2013
Location: W Washington
Karma: 2
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Senior Member |
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I'd suggest running 195 stat - this does not hurt your cooling system and it helps to keep the oil temp closer to the boil off point for various condensates.
Open loop- this means there is no feedback from the o2 sensor. The fuel delivery will be based on pre-determined mapping such as VE. VE is volumetric efficiency - the amount of air ingested at a particular speed and load as a fraction of the total volume (at WOT you might be near 95% of those 455 cubes, but coasting it will be more like 10%). The fuel delivery could be based on mass air flow if equipped with a MAF sensor.
- closed loop - the o2 sensor has to get hot enough to function. It develops a voltage based on presence or absence of O2 in the exhaust. The o2 sensor switches from high to low voltage (and back) at 14.7:1 on gasoline. The control strategies work as follows; read "rich" or low voltage and the system will shift lean. Then when the ECM sees "lean" it shifts rich again. The fuel control will dither back and forth across the nominal point of 14.7:1 with pretty tight control, typically + and - only 0.1 or 0.2 A/F ratios. The systems usually will shift into an open loop rich mode at wide open throttle. The above applies to "switching" o2 sensors. Many cars in the past 10 years have adopted wide-band or linear lambda systems - a topic for another post.
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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