Temp gauge reads wrong! - The 1947 - Present Chevrolet & GMC Truck Message Board Network

jeffs98 · 03-13-2005, 04:57 PM

I have a 78 chevy and it has a new (tried numerous ones) temp sender in it and the gauge reads too high, actually the gauge starts reading that motor is getting warm way too fast!What i mean is that i can start the truck up and in no time the gauge starts rising past the 100 deg mark and on up!
I was told by a gauge repairman that this is not a sign of a bad gauge, he said it is the sender! I was wondering what this board thought as i always get correct answers here and am tired of messing with it! I am to the point now of trying to ohm test wires to gauge to see if one is partially shorted to ground! If the wrong temp. gauge was in it, would it do this or is that possible? Thanks!!
The temperature gauge in it has the temp numbers starting at 100 deg. i have noticed lots of older trucks having the ones that go cold to hot!! Just thought this might help!!

**Palf70Step** · 03-13-2005, 05:21 PM

Two things come to mind...Guage is bad...

Or maybe you have a temp sensor for an idiot light and not a gauge. That'll mess up your readings alot.

pedrofixlater · 03-13-2005, 08:28 PM

Take the wire of the sending unit and ground it if your gauge maxes out the gauge is fine.

jeffs98 · 03-13-2005, 09:36 PM

Gauge does max out if you ground the wire and it is a sending unit for a gauge not an idiot light!

**76sierraclassic** · 03-13-2005, 10:18 PM

When I got my '76 GMC, the temp guage didn't work at all. I changed out the sending unit, and it started doing exactly what you are describing; about a half mile down the road, it started to skyrocket, and pegged out. I took the sending unit back to O'Reillys and got another one, and it works just fine. Just for reference, both of the sending units were Borg Warner.

Mike

ureckme · 03-13-2005, 10:23 PM

Wrong!. This is what the prob is, older trucks use a 80 ohm sender witch is the larger sender. The newer ( 80? ) have a smaller sender 160 ohm. That is 160 or 80 ohm at 220F I put newer heads on my 73 C10 and the gauge would read low, the fix on mine was 2 senders 1 in each head. The newer trucks with the large sender will read to hot. Matt

jeffs98 · 03-14-2005, 02:32 AM

Ok ureckme,i think you lost me, maybe,or not?!! So you put two senders in, one in each head, and hooked up the wiring ??Couldn't you of just got the correct unit and installed it instead of doubling the resistance with two sending units!???

It is in a 78 and i have a thorsen tsu5 sending unit in it now!! I have had a lot of gauge repairs done lately on the 82 dump truck that i bought and the guy that has the gauge repair shop tells me that these are the most accurate sending unit inthe world! He also did not mention anything about the difference in the ohm specs from newer years and older years of chevy sending units!! I am going to look into this though and get back with ya!

ureckme · 03-14-2005, 04:41 AM

The correct sender would not fit in the newer heads. I have a 73 with 89+- to 95 heads. Thay have a small hole. 73 have a large hole. I found this out from a NAPA book. Mine needs 80ohms, the later heads ( smaller hole ) 160ohms, 2 160ohm senders is 80ohms at 220f. Heat up some water put your gauge wire on your sender, ground the outer part of the sender with an extra wire and drop it in hot water. But first did your gauge ever read right. My parts guy gave me at first the wrong sender for a f@rd and my gauge went sky high. The next one for the newer heads would bearly read 1/2 what it should, and 2 was right on, one in each head. Matt

jeffs98 · 03-14-2005, 07:12 AM

I don't know if it was ever right as it wasn't hooked up when i got the truck and now am getting around to fixing it! I just put a temp. gun on it and knew how hot it was even though the temp gauge was wrong!

ureckme · 03-15-2005, 12:21 AM

This is a pic of my original 73 sender ( left ) the other is for size (right). Matt

jeffs98 · 03-15-2005, 09:11 PM

The one on the left is the one that i have in the truck engine!! It is the same on both of the trucks that i got!! It just seems that there are two different gauge styles, i don't know why i think that but it just seems that way!! I thought that there was a gauge with a cold to hot reading and then there was a gauge with a specific temp reading on it!! I wonder if the cluster has to match the gauge itself or not???

Lynx · 03-15-2005, 09:19 PM

Hook a multimeter up to your sender and then to ground. This will tell you what kind of signal your sender is putting out(just to make sure its working properly).

Your Gauge will have to match the sender or else it will read diffrent then what the actual temp is. However if your using a 73-87 sender and gauge you should be fine since gm didnt change the actual mechanics of the gauage in this time period.

Edit: Forgot to mention that if you are running newer heads and your old sender wont fit in the hole provided all you need to do is go down to your local hardware store and pick up some NPT fittings.

ureckme · 03-15-2005, 09:33 PM

The gauge with the cold / hot goes with the sender in pic. The other with numbers takes a 160 ohm sender, its a smaller sender or one the same size with a spade on top?.Matt

jeffs98 · 03-15-2005, 09:40 PM

ureckme,I wonder what year of vehicle you could go to to get the correct one then for my truck!! I have the one in my truck with the temp readings and not with a top stud!! Lynx, i am going to get a reading @ sender and at dash and see if they are the same!!Thanks!!

ureckme · 03-15-2005, 10:10 PM

not sure of year, mid 80s and newer.Matt

jeffs98 · 03-15-2005, 10:14 PM

I called o'reillys and got one! It is for an 84 chevy! We'll see if it works!!!Thanks for all the input guys! I'll let ya know what i find out!!

03-13-2005, 04:57 PM	#1
jeffs98 Registered User Join Date: Jun 2004 Location: Parsons, Kansas Posts: 139	Temp gauge reads wrong! I have a 78 chevy and it has a new (tried numerous ones) temp sender in it and the gauge reads too high, actually the gauge starts reading that motor is getting warm way too fast!What i mean is that i can start the truck up and in no time the gauge starts rising past the 100 deg mark and on up! I was told by a gauge repairman that this is not a sign of a bad gauge, he said it is the sender! I was wondering what this board thought as i always get correct answers here and am tired of messing with it! I am to the point now of trying to ohm test wires to gauge to see if one is partially shorted to ground! If the wrong temp. gauge was in it, would it do this or is that possible? Thanks!! The temperature gauge in it has the temp numbers starting at 100 deg. i have noticed lots of older trucks having the ones that go cold to hot!! Just thought this might help!! __________________ 1978 Chevy C-60 Pumper Truck! 1985 Chevy 4x4 project! 2002 Chevy Crew Cab DURAMAX 4x4!! 2002 Harley Road King BIG BORE STG. II, Thunderheader,Dfo Module! 2003 Chevy Malibu!

03-13-2005, 05:21 PM	#2
Palf70Step State of Confusion! Join Date: Jul 2002 Location: Gulfport, MS USA Posts: 46,787	Two things come to mind...Guage is bad... Or maybe you have a temp sensor for an idiot light and not a gauge. That'll mess up your readings alot. __________________ Bill 1970 Chevy Custom/10 LWB Fleetside 2010 Toyota Tacoma PreRunner SR5 Double Cab - DD Member of Louisiana Classic Truck Club (LCTC) Bill's Gallery Life isn't tied with a bow, but it's still a gift. Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God!

03-13-2005, 08:28 PM	#3
pedrofixlater 75 STEPSIDE Join Date: Mar 2005 Location: Suffolk, VA Posts: 92	Take the wire of the sending unit and ground it if your gauge maxes out the gauge is fine. __________________ Pete 75 Chevy Stepside 70 Buick Skylark/GS

03-13-2005, 09:36 PM	#4
jeffs98 Registered User Join Date: Jun 2004 Location: Parsons, Kansas Posts: 139	Gauge does max out if you ground the wire and it is a sending unit for a gauge not an idiot light! __________________ 1978 Chevy C-60 Pumper Truck! 1985 Chevy 4x4 project! 2002 Chevy Crew Cab DURAMAX 4x4!! 2002 Harley Road King BIG BORE STG. II, Thunderheader,Dfo Module! 2003 Chevy Malibu!

03-14-2005, 02:32 AM	#7
jeffs98 Registered User Join Date: Jun 2004 Location: Parsons, Kansas Posts: 139	Ok ureckme,i think you lost me, maybe,or not?!! So you put two senders in, one in each head, and hooked up the wiring ??Couldn't you of just got the correct unit and installed it instead of doubling the resistance with two sending units!??? It is in a 78 and i have a thorsen tsu5 sending unit in it now!! I have had a lot of gauge repairs done lately on the 82 dump truck that i bought and the guy that has the gauge repair shop tells me that these are the most accurate sending unit inthe world! He also did not mention anything about the difference in the ohm specs from newer years and older years of chevy sending units!! I am going to look into this though and get back with ya! __________________ 1978 Chevy C-60 Pumper Truck! 1985 Chevy 4x4 project! 2002 Chevy Crew Cab DURAMAX 4x4!! 2002 Harley Road King BIG BORE STG. II, Thunderheader,Dfo Module! 2003 Chevy Malibu!

03-13-2005, 10:18 PM	#5
76sierraclassic Senior Member Join Date: Feb 2004 Location: White Hall, AR Posts: 316	When I got my '76 GMC, the temp guage didn't work at all. I changed out the sending unit, and it started doing exactly what you are describing; about a half mile down the road, it started to skyrocket, and pegged out. I took the sending unit back to O'Reillys and got another one, and it works just fine. Just for reference, both of the sending units were Borg Warner. Mike

03-13-2005, 10:23 PM	#6
ureckme ureckmefixit2@cox.net Join Date: Dec 2004 Location: Mesa AZ. (Phoenix) Posts: 1,284	Wrong!. This is what the prob is, older trucks use a 80 ohm sender witch is the larger sender. The newer ( 80? ) have a smaller sender 160 ohm. That is 160 or 80 ohm at 220F I put newer heads on my 73 C10 and the gauge would read low, the fix on mine was 2 senders 1 in each head. The newer trucks with the large sender will read to hot. Matt

03-14-2005, 04:41 AM	#8
ureckme ureckmefixit2@cox.net Join Date: Dec 2004 Location: Mesa AZ. (Phoenix) Posts: 1,284	The correct sender would not fit in the newer heads. I have a 73 with 89+- to 95 heads. Thay have a small hole. 73 have a large hole. I found this out from a NAPA book. Mine needs 80ohms, the later heads ( smaller hole ) 160ohms, 2 160ohm senders is 80ohms at 220f. Heat up some water put your gauge wire on your sender, ground the outer part of the sender with an extra wire and drop it in hot water. But first did your gauge ever read right. My parts guy gave me at first the wrong sender for a f@rd and my gauge went sky high. The next one for the newer heads would bearly read 1/2 what it should, and 2 was right on, one in each head. Matt

03-14-2005, 07:12 AM	#9
jeffs98 Registered User Join Date: Jun 2004 Location: Parsons, Kansas Posts: 139	I don't know if it was ever right as it wasn't hooked up when i got the truck and now am getting around to fixing it! I just put a temp. gun on it and knew how hot it was even though the temp gauge was wrong! __________________ 1978 Chevy C-60 Pumper Truck! 1985 Chevy 4x4 project! 2002 Chevy Crew Cab DURAMAX 4x4!! 2002 Harley Road King BIG BORE STG. II, Thunderheader,Dfo Module! 2003 Chevy Malibu!

03-15-2005, 12:21 AM	#10
ureckme ureckmefixit2@cox.net Join Date: Dec 2004 Location: Mesa AZ. (Phoenix) Posts: 1,284	This is a pic of my original 73 sender ( left ) the other is for size (right). Matt Attached Images

03-15-2005, 09:11 PM	#11
jeffs98 Registered User Join Date: Jun 2004 Location: Parsons, Kansas Posts: 139	The one on the left is the one that i have in the truck engine!! It is the same on both of the trucks that i got!! It just seems that there are two different gauge styles, i don't know why i think that but it just seems that way!! I thought that there was a gauge with a cold to hot reading and then there was a gauge with a specific temp reading on it!! I wonder if the cluster has to match the gauge itself or not??? __________________ 1978 Chevy C-60 Pumper Truck! 1985 Chevy 4x4 project! 2002 Chevy Crew Cab DURAMAX 4x4!! 2002 Harley Road King BIG BORE STG. II, Thunderheader,Dfo Module! 2003 Chevy Malibu!

03-15-2005, 09:19 PM	#12
Lynx Registered User Join Date: Jun 2003 Location: Fort McMurray, Alberta, Canada Posts: 513	Hook a multimeter up to your sender and then to ground. This will tell you what kind of signal your sender is putting out(just to make sure its working properly). Your Gauge will have to match the sender or else it will read diffrent then what the actual temp is. However if your using a 73-87 sender and gauge you should be fine since gm didnt change the actual mechanics of the gauage in this time period. Edit: Forgot to mention that if you are running newer heads and your old sender wont fit in the hole provided all you need to do is go down to your local hardware store and pick up some NPT fittings. __________________ Ben 1983 Silverado SWB 305 2002 Silverado Extended Cab 5.3 http://members.shaw.ca/bkennett Last edited by Lynx; 03-15-2005 at 09:25 PM.

03-15-2005, 09:33 PM	#13
ureckme ureckmefixit2@cox.net Join Date: Dec 2004 Location: Mesa AZ. (Phoenix) Posts: 1,284	The gauge with the cold / hot goes with the sender in pic. The other with numbers takes a 160 ohm sender, its a smaller sender or one the same size with a spade on top?.Matt

03-15-2005, 09:40 PM	#14
jeffs98 Registered User Join Date: Jun 2004 Location: Parsons, Kansas Posts: 139	ureckme,I wonder what year of vehicle you could go to to get the correct one then for my truck!! I have the one in my truck with the temp readings and not with a top stud!! Lynx, i am going to get a reading @ sender and at dash and see if they are the same!!Thanks!! __________________ 1978 Chevy C-60 Pumper Truck! 1985 Chevy 4x4 project! 2002 Chevy Crew Cab DURAMAX 4x4!! 2002 Harley Road King BIG BORE STG. II, Thunderheader,Dfo Module! 2003 Chevy Malibu!

03-15-2005, 10:10 PM	#15
ureckme ureckmefixit2@cox.net Join Date: Dec 2004 Location: Mesa AZ. (Phoenix) Posts: 1,284	not sure of year, mid 80s and newer.Matt



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03-15-2005, 10:14 PM	#16
jeffs98 Registered User Join Date: Jun 2004 Location: Parsons, Kansas Posts: 139	I called o'reillys and got one! It is for an 84 chevy! We'll see if it works!!!Thanks for all the input guys! I'll let ya know what i find out!! __________________ 1978 Chevy C-60 Pumper Truck! 1985 Chevy 4x4 project! 2002 Chevy Crew Cab DURAMAX 4x4!! 2002 Harley Road King BIG BORE STG. II, Thunderheader,Dfo Module! 2003 Chevy Malibu!

Register or Log In To remove these advertisements.