Temp Gauge Isnt Working - The 1947 - Present Chevrolet & GMC Truck Message Board Network

jjg · 07-13-2002, 07:34 PM

hey guys
My temp gauge is gonna drive me nuts i dont know if it is my temp unit or my gauge or what. But this is what i did.
I went and purchase a new unit ran a wire from that to the bottom peg on the back of the gauge then ran wire from the top peg to the fuse box that has 12 volts when the switch is on... DID I DO THIS CORRECTLY???? The gauge just sits on the C and will not move anyway to check the gauge to make sure it is working properly? Any help would be appreciated.
John

mikep · 07-13-2002, 08:07 PM

stock gauges are calibrated with 195 degree thermostats if I am not mistaken. If you use a 180 degree thermostat it will sit right on the C. Thats where mine sits too. It started sitting there when i put a 180 thermostat instead of the 195 so that sort of tipped me off...Duh.. You'll know if it starts to get hot as it will rise off the "C" and travel where the "H" is.

Longhorn Man · 07-13-2002, 09:26 PM

Is this a stock type guage..or an aftermarket?
No matter what temp your thermostat is, it should read.

mikep · 07-13-2002, 10:48 PM

Its not going to read anything if the operating temperature of the engine is below the operating range of the gauge. Stock gauges are calibrated to read in the normal range at 195 degrees. If your engine temperature is only 180 then the gauge will not be in its operating range and will show C since the gauge is calibrated to show C at 180 degrees. Thats why mine shows C at 180 degrees. If I had a 195 thermostat it would read in the middle of the gauges range. If I had a 210 thermostat it would read in the H area of the gauge.

Bill72BB · 07-13-2002, 10:58 PM

I've run 160 ,180. and 190 Degree thermostats and have always had some reading ,
Right now I run a 180 and the temp gauge is at about what the 1/4 full mark would be if it was a gas gauge .

Bill

mikep · 07-13-2002, 11:03 PM

Mine is calibrated to 195 and doesnt move over C at 180. If you have one that is calibrated at 180 as many were then it will show a higher reading. Different engines and years used different temp thermostats and a different gauge setting corresponding to that thermostat.

Longhorn Man · 07-13-2002, 11:06 PM

Thank you Bill, That is what was in my head...but not gettinng typed.
The guage shows a range of temps...from cold, (say 150 degrees) to hot. (probably about 250) Otherwise, it would only tell you when you are at operating temps, and nothng else, and then it would be of no info...worse than a dummy light.
Just like the disclamer in the owners manual that says you must keep it at a 50/50 mixture....B.S. Temp is temp, be it water, oil, air, or green radiater goo. (I have confirmed this too) The reason they say 50/50 on that, is to make you think that is the case, and you (the owner...not YOU) are fooled into doing 50/50 and they would have less warantee claims for cracked blocks and the like.
Water is also the best coolant, but that is a whole thread in its self.

mikep · 07-13-2002, 11:16 PM

The bit about coolant is wrong too but that is another discussion as you have stated. heat transfer is much faster for ethylene or propylene glycol than straight water.
The gauge is really only there to tell you if its too hot. The range of the guage on a engine that is designed to run at 195 is more like 175-260 degrees on these trucks or at least it was on the last 3 I have owned which all did the same thing when i put 180 degree thermostats in them. It also depends on the sending unit calibration.

RipMeyer · 07-14-2002, 12:11 AM

I dont understand what you mean the gage is calibrated to a thermostat? Its just a gauge with a range. Not matter if the thermostat is 160 ,180 or 195. The gage will still read. the sending unit is the only factor. For example if the top end of the scal is 250 and the low is 100. no matter what thermostat is in there it will always show the temp accordingly. 100 low, 250 high. Temostat has no bearing on the gage reading the temp.

Longhorn Man · 07-14-2002, 12:50 AM

Is a rectal thermometer calibrated to your @ss verses an oral one calibrated to your mouth?
A thermometer is a thermometer is a thermometer.

RipMeyer · 07-14-2002, 01:50 AM

Do you believe the themostat changes the range of the gage? The thermostat is not a factor. It still reads correctly even if you take out the thermostat.

RipMeyer · 07-14-2002, 01:53 AM

Confused

Are you making my point or contesting it?

mikep · 07-14-2002, 02:18 AM

OK lets try this again. Pretend you are an engineer working at General motors in 1966. Boss Kettering has given you the assignment of designing a temperature gauge to mount in the new chevrolet truck line. You have decided to make a "relative scale" instead of an "absolute scale" gauge as is the custom of the time. A relative scale gauge is a gauge that has C on one side and an H on the other to signify cold or hot. Since the boys over at engine design have decided that the new truck line will use a 195 degree thermostat in most of the models you design the gauge so that the "C" corresponds to an engine coolant temperature of 180 degrees and so that "H" corresponds to an engine coolant temperature of 260 degrees because you can not build a gauge that has a full temperature range from 100-300 degrees and have it

a. legible. Its a small gauge.

and

b. accurate . Analog gauges of this type are only accurate in the middle of their scale.

So with a 195 degree thermostat the gauge will read in the normal area which is about 1/3 from the left. You want the driver to know if the engine is overheating so you allow more room on the right side of the gauge since the greatest damage to the engine can occur when it is overheating. If it were an absolute scale readout gauge the driver could look at the gauge and tell the exact temperature of the engine. If it were 180 the gauge would say 180 degrees but the gauges in these trucks do not do that do they. They just tell you if they are hot or cold relative to their design calibration which in this case means a normal operating temperature of 195 degrees.

Years later some guy comes along and decides to change the thermostat so that the engine coolant will operate at 180 degrees instead of 195 degrees as was originally intended and then wonders why the gauge isnt working properly and insists that the gauge must be wrong when it is doing exactly what the designer intended it to do 37 years ago and that is show an engine coolant temperature of 180 degrees on a relative scale where C=180F and H=260F.

But what the hell do I know ? I only took 2 years of instrumentation and control technology in college , have been working in the field for 14 years and I spend a good third of every working day servicing and calibrating control instrumentation and working on glycol to water chillers.

RipMeyer · 07-14-2002, 02:34 AM

The gage has nothing to do with the temp. its simply a voltmeter.
the sending unit / THERMOCOUPLE is the only factor.

Example
the gage responds full scale with 4 millivolts, the sending unit/THERMO COUPLE puts out 4 millivolts at 250 deg. the gage has no idea that it has a thermostat in the engine and doesnt care. you could use a sending unit/THERMOCOUPLE that put out 4 millivolts at 2000 deg and that gage in your truck would work just fine but would read full scale at 2000 deg. over simplified but you get the point

mikep · 07-14-2002, 02:40 AM

That is right. The calibration of the gauge is matched to the calibration of the sending unit. The sending unit is calibrated to begin letting voltage through at a preset temperature. In this case we are assuming its 180 degrees which corresponds to the C mark on the gauge. Change the sending unit, Take care of the problem or alter the calibration of the gauge and accomplish the same thing. Point is that when the thermostat was changed from 195 to a lower temperature it changed the temperature of the coolant which changed where on the gauge the needle was pointing. Can we agree on that? I have changed several of them in the past from 195 to 180 and seen the same thing happen every time with each hovering around the C mark until they overheated and raised into the higher range on the gauge .

RipMeyer · 07-14-2002, 02:53 AM

Ok we seem to agree alittle. However the gage and thermostat is still not a factor.
with the current sending unit, lets just say full scale is 250. no matter what 250 is its max temp. right? so lets say we have a 160 themostat and your truck heats up to 200 and it reads 3/4 of full scale. now lets put in a 195 thermostat and your truck heats up to 200. Its gonna read the same spot at 3/4 of full scale because the sendind unit puts out the same voltage..

The thermostat has nothing to do with it.

jjg · 07-14-2002, 03:00 AM

OK thanks for all the input , but i dont think i am any closer to understanding the problem
John

RipMeyer · 07-14-2002, 03:03 AM

What was your question?

Just kidding.

Ok, what is it exactly you bought? Did you buy a mechanical gage?
Electric? Change sending unit?

jjg · 07-14-2002, 03:08 AM

Well it is the original style gauge that came with these trucks, I went ahead and got a new temp unit, but is there a way to make sure the sending unit actually works??? Or how bout a way to test to see if the gauge is shot or not. Do the gauges usually crap out or is it something else.
thanks
John

RipMeyer · 07-14-2002, 03:30 AM

ok, I dont have an answer but I have the question that if answered will.

Does the meter movement get power from the sending unit alone? And not 12 volts. If so you may have fried the gage.

Anyone?

LILREDGMC · 07-14-2002, 09:13 AM

Just my 2 cents, from memory, as it fades a bit, if you pull the wire off the sending unit, and take it to ground, the gauge should go full scale. Open circuit would equal no output, grounded circuit would drive the needle to full scale. I haven't walked out and done it to confirm, but this is my recall. Anyone else.

Longhorn Man · 07-14-2002, 11:26 AM

So the Temp guage is the same then. Thats what i was trying to say in the first place. The guage should give a reading even when a slightly cooler reading is there regardless. It won't come much off the cold when running a 160 stat in it, but it will come up a bit.

mikep · 07-14-2002, 11:49 AM

I guess the real question here is if the engine starts to get hot does your needle move ? Pull the fan belt off and run it for a few minutes then shut it down. see if it starts to get hot or not. see if the needle moves.

jjg · 07-14-2002, 12:54 PM

yeah the needle does not move at all, so i am guessing it is my gauge, i have another stock one but i have no idea about the condition is there a way to bench test it to see if it works????
John

mikep · 07-14-2002, 02:23 PM

are you sure you have a graduated sensor and not a n on/off idiot light sensor?

07-13-2002, 07:34 PM	#1
jjg Registered User Join Date: Mar 2000 Location: elk horn, ia, USA Posts: 554	Temp Gauge Isnt Working hey guys My temp gauge is gonna drive me nuts i dont know if it is my temp unit or my gauge or what. But this is what i did. I went and purchase a new unit ran a wire from that to the bottom peg on the back of the gauge then ran wire from the top peg to the fuse box that has 12 volts when the switch is on... DID I DO THIS CORRECTLY???? The gauge just sits on the C and will not move anyway to check the gauge to make sure it is working properly? Any help would be appreciated. John

07-13-2002, 08:07 PM	#2
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	stock gauges are calibrated with 195 degree thermostats if I am not mistaken. If you use a 180 degree thermostat it will sit right on the C. Thats where mine sits too. It started sitting there when i put a 180 thermostat instead of the 195 so that sort of tipped me off...Duh.. You'll know if it starts to get hot as it will rise off the "C" and travel where the "H" is. __________________ No truck :-(

07-13-2002, 10:48 PM	#4
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	Its not going to read anything if the operating temperature of the engine is below the operating range of the gauge. Stock gauges are calibrated to read in the normal range at 195 degrees. If your engine temperature is only 180 then the gauge will not be in its operating range and will show C since the gauge is calibrated to show C at 180 degrees. Thats why mine shows C at 180 degrees. If I had a 195 thermostat it would read in the middle of the gauges range. If I had a 210 thermostat it would read in the H area of the gauge. __________________ No truck :-(

07-13-2002, 10:58 PM	#5
Bill72BB Thats the Hillbilly way Join Date: Jul 2001 Location: Torrance,Ca Posts: 5,979	I've run 160 ,180. and 190 Degree thermostats and have always had some reading , Right now I run a 180 and the temp gauge is at about what the 1/4 full mark would be if it was a gas gauge . Bill __________________ BILL Torrance Calif 90504 Member DUF Club Member Old Farts Club 72 3/4ton Custom Camper BB402/400 trans Dynomax Cerama-coat headers , Hei distributor ,Edelbrock 1411 air,ps,pb,leafsprings ,98 chevy 60/40 seat,S10 shoulder belts tilt,3.54 Dana 60 rear. 16" Eagle wheels with LT265/75 16 tires,Gaylord Lid,H4 headlights with 100W relay conversion. " If I knew I was going to live this long I would have taken better care of myself " Marriage changes passion...suddenly you're in bed with a relative. A GUY'S PRAYER.... Lord, I pray for a nympho with huge boobs who owns a liquor store and likes to fish and hunt and has a Harley .Amen ,

07-13-2002, 11:03 PM	#6
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	Mine is calibrated to 195 and doesnt move over C at 180. If you have one that is calibrated at 180 as many were then it will show a higher reading. Different engines and years used different temp thermostats and a different gauge setting corresponding to that thermostat. __________________ No truck :-(

07-13-2002, 09:26 PM	#3
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Is this a stock type guage..or an aftermarket? No matter what temp your thermostat is, it should read.

07-13-2002, 11:06 PM	#7
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Thank you Bill, That is what was in my head...but not gettinng typed. The guage shows a range of temps...from cold, (say 150 degrees) to hot. (probably about 250) Otherwise, it would only tell you when you are at operating temps, and nothng else, and then it would be of no info...worse than a dummy light. Just like the disclamer in the owners manual that says you must keep it at a 50/50 mixture....B.S. Temp is temp, be it water, oil, air, or green radiater goo. (I have confirmed this too) The reason they say 50/50 on that, is to make you think that is the case, and you (the owner...not YOU) are fooled into doing 50/50 and they would have less warantee claims for cracked blocks and the like. Water is also the best coolant, but that is a whole thread in its self.

07-13-2002, 11:16 PM	#8
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	The bit about coolant is wrong too but that is another discussion as you have stated. heat transfer is much faster for ethylene or propylene glycol than straight water. The gauge is really only there to tell you if its too hot. The range of the guage on a engine that is designed to run at 195 is more like 175-260 degrees on these trucks or at least it was on the last 3 I have owned which all did the same thing when i put 180 degree thermostats in them. It also depends on the sending unit calibration. __________________ No truck :-(

07-14-2002, 12:11 AM	#9
RipMeyer Registered User Join Date: Oct 2001 Location: Southern New Mexico Posts: 649	I dont understand what you mean the gage is calibrated to a thermostat? Its just a gauge with a range. Not matter if the thermostat is 160 ,180 or 195. The gage will still read. the sending unit is the only factor. For example if the top end of the scal is 250 and the low is 100. no matter what thermostat is in there it will always show the temp accordingly. 100 low, 250 high. Temostat has no bearing on the gage reading the temp.

07-14-2002, 12:50 AM	#10
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Is a rectal thermometer calibrated to your @ss verses an oral one calibrated to your mouth? A thermometer is a thermometer is a thermometer. Last edited by Longhorn Man; 07-14-2002 at 12:56 AM.

07-14-2002, 01:50 AM	#11
RipMeyer Registered User Join Date: Oct 2001 Location: Southern New Mexico Posts: 649	Do you believe the themostat changes the range of the gage? The thermostat is not a factor. It still reads correctly even if you take out the thermostat.

07-14-2002, 01:53 AM	#12
RipMeyer Registered User Join Date: Oct 2001 Location: Southern New Mexico Posts: 649	Confused Are you making my point or contesting it?

07-14-2002, 02:18 AM	#13
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	OK lets try this again. Pretend you are an engineer working at General motors in 1966. Boss Kettering has given you the assignment of designing a temperature gauge to mount in the new chevrolet truck line. You have decided to make a "relative scale" instead of an "absolute scale" gauge as is the custom of the time. A relative scale gauge is a gauge that has C on one side and an H on the other to signify cold or hot. Since the boys over at engine design have decided that the new truck line will use a 195 degree thermostat in most of the models you design the gauge so that the "C" corresponds to an engine coolant temperature of 180 degrees and so that "H" corresponds to an engine coolant temperature of 260 degrees because you can not build a gauge that has a full temperature range from 100-300 degrees and have it a. legible. Its a small gauge. and b. accurate . Analog gauges of this type are only accurate in the middle of their scale. So with a 195 degree thermostat the gauge will read in the normal area which is about 1/3 from the left. You want the driver to know if the engine is overheating so you allow more room on the right side of the gauge since the greatest damage to the engine can occur when it is overheating. If it were an absolute scale readout gauge the driver could look at the gauge and tell the exact temperature of the engine. If it were 180 the gauge would say 180 degrees but the gauges in these trucks do not do that do they. They just tell you if they are hot or cold relative to their design calibration which in this case means a normal operating temperature of 195 degrees. Years later some guy comes along and decides to change the thermostat so that the engine coolant will operate at 180 degrees instead of 195 degrees as was originally intended and then wonders why the gauge isnt working properly and insists that the gauge must be wrong when it is doing exactly what the designer intended it to do 37 years ago and that is show an engine coolant temperature of 180 degrees on a relative scale where C=180F and H=260F. But what the hell do I know ? I only took 2 years of instrumentation and control technology in college , have been working in the field for 14 years and I spend a good third of every working day servicing and calibrating control instrumentation and working on glycol to water chillers. __________________ No truck :-( Last edited by mikep; 07-14-2002 at 02:35 AM.

07-14-2002, 02:34 AM	#14
RipMeyer Registered User Join Date: Oct 2001 Location: Southern New Mexico Posts: 649	The gage has nothing to do with the temp. its simply a voltmeter. the sending unit / THERMOCOUPLE is the only factor. Example the gage responds full scale with 4 millivolts, the sending unit/THERMO COUPLE puts out 4 millivolts at 250 deg. the gage has no idea that it has a thermostat in the engine and doesnt care. you could use a sending unit/THERMOCOUPLE that put out 4 millivolts at 2000 deg and that gage in your truck would work just fine but would read full scale at 2000 deg. over simplified but you get the point

07-14-2002, 02:40 AM	#15
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	That is right. The calibration of the gauge is matched to the calibration of the sending unit. The sending unit is calibrated to begin letting voltage through at a preset temperature. In this case we are assuming its 180 degrees which corresponds to the C mark on the gauge. Change the sending unit, Take care of the problem or alter the calibration of the gauge and accomplish the same thing. Point is that when the thermostat was changed from 195 to a lower temperature it changed the temperature of the coolant which changed where on the gauge the needle was pointing. Can we agree on that? I have changed several of them in the past from 195 to 180 and seen the same thing happen every time with each hovering around the C mark until they overheated and raised into the higher range on the gauge . __________________ No truck :-( Last edited by mikep; 07-14-2002 at 02:45 AM.



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07-14-2002, 02:53 AM	#16
RipMeyer Registered User Join Date: Oct 2001 Location: Southern New Mexico Posts: 649	Ok we seem to agree alittle. However the gage and thermostat is still not a factor. with the current sending unit, lets just say full scale is 250. no matter what 250 is its max temp. right? so lets say we have a 160 themostat and your truck heats up to 200 and it reads 3/4 of full scale. now lets put in a 195 thermostat and your truck heats up to 200. Its gonna read the same spot at 3/4 of full scale because the sendind unit puts out the same voltage.. The thermostat has nothing to do with it. Last edited by RipMeyer; 07-14-2002 at 02:57 AM.

07-14-2002, 03:00 AM	#17
jjg Registered User Join Date: Mar 2000 Location: elk horn, ia, USA Posts: 554	OK thanks for all the input , but i dont think i am any closer to understanding the problem John

07-14-2002, 03:03 AM	#18
RipMeyer Registered User Join Date: Oct 2001 Location: Southern New Mexico Posts: 649	What was your question? Just kidding. Ok, what is it exactly you bought? Did you buy a mechanical gage? Electric? Change sending unit?

07-14-2002, 03:08 AM	#19
jjg Registered User Join Date: Mar 2000 Location: elk horn, ia, USA Posts: 554	Well it is the original style gauge that came with these trucks, I went ahead and got a new temp unit, but is there a way to make sure the sending unit actually works??? Or how bout a way to test to see if the gauge is shot or not. Do the gauges usually crap out or is it something else. thanks John

07-14-2002, 03:30 AM	#20
RipMeyer Registered User Join Date: Oct 2001 Location: Southern New Mexico Posts: 649	ok, I dont have an answer but I have the question that if answered will. Does the meter movement get power from the sending unit alone? And not 12 volts. If so you may have fried the gage. Anyone?

07-14-2002, 09:13 AM	#21
LILREDGMC Registered User Join Date: Oct 2001 Location: Pittsburgh, Pennsylvania USA Posts: 461	Temperature Just my 2 cents, from memory, as it fades a bit, if you pull the wire off the sending unit, and take it to ground, the gauge should go full scale. Open circuit would equal no output, grounded circuit would drive the needle to full scale. I haven't walked out and done it to confirm, but this is my recall. Anyone else.

07-14-2002, 11:26 AM	#22
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	So the Temp guage is the same then. Thats what i was trying to say in the first place. The guage should give a reading even when a slightly cooler reading is there regardless. It won't come much off the cold when running a 160 stat in it, but it will come up a bit.

07-14-2002, 11:49 AM	#23
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	I guess the real question here is if the engine starts to get hot does your needle move ? Pull the fan belt off and run it for a few minutes then shut it down. see if it starts to get hot or not. see if the needle moves. __________________ No truck :-(

07-14-2002, 12:54 PM	#24
jjg Registered User Join Date: Mar 2000 Location: elk horn, ia, USA Posts: 554	yeah the needle does not move at all, so i am guessing it is my gauge, i have another stock one but i have no idea about the condition is there a way to bench test it to see if it works???? John

07-14-2002, 02:23 PM	#25
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	are you sure you have a graduated sensor and not a n on/off idiot light sensor? __________________ No truck :-(

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