Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

name

OBS Enthusiast
Joined
Aug 9, 2019
Messages
81
Reaction score
41
Location
ohio
Hi Guys,

I have a 1994 GMC suburban that I am trying to figure out why the temp gauge always reads low, I have tried to diagnose it before with no luck and when looking into it a second time I found something interesting and wanted to run it past you guys.

But first a little history :

A couple years back I got a new to me '94 suburban and when trying to diagnose a low reading temp gauge I replaced the sending unit by the spark plugs and thermostat ( 190 deg ) It did not cure my problem and I just lived with it. But now after flushing and replacing my coolant it seems to read even lower than it did before ( currently 140 max) so I decided to look into it again.

Here is what I got :

1) The suburban does get warm and throws good heat ( 120 - 140 deg. air out of the center vent according to an IR gun )
2) The IR gun shows 160-180 ish at the thermostat housing .
3) The gauge does not show movement when the thermostat opens up, but I can see it on the IR gun at the Thermostat housing ( about a 20 deg swing )
4) The hoses do get hot as you would expect .
5) No signs of overheating , but it does seem like a pig that cant get out of it way at times.


What I found is that the sending unit that I replaced a couple of years ago has 2 prongs in it , but the wiring harnes only has one wire. Not sure if this is the problem because it has always read low on the temp gauge . ( I probably just took the old unit to the part store so they could match up what was in there )

Is this the wrong sending unit for my application, or does this sending unit fit more than one application and is not the problem ?

Here are some pictures :
 

Attachments

  • IMG_0100.JPG
    IMG_0100.JPG
    228.7 KB · Views: 35
  • IMG_0089.JPG
    IMG_0089.JPG
    354.2 KB · Views: 34
  • IMG_0090.JPG
    IMG_0090.JPG
    292.6 KB · Views: 28
  • IMG_0095.JPG
    IMG_0095.JPG
    289 KB · Views: 25
  • IMG_0096.JPG
    IMG_0096.JPG
    265.5 KB · Views: 34

dave s

I'm Awesome
Joined
Oct 25, 2019
Messages
232
Reaction score
392
Location
pa
I don't have a solution but I have the exact issue with my 94. I have only changed the thermostat. Sender is on the shelf. I'll be paying attention to what you find out. I also used the IR gun and do see good temps on motor and heater. I haven't licensed it yet so it hasn't been an issue. I was thinking my gauge was just bad....
 

Ron88

Newbie
Joined
Jul 29, 2017
Messages
23
Reaction score
18
Location
08721
the one yhat you are holding looks like the sender that goes by the thermostat housing it tells the computer what temperature the engine is. The one you want is usually in the drivers side cylinder head and is a one wire hookup.
 

Das Hatt

OBS Enthusiast
Joined
Nov 14, 2021
Messages
79
Reaction score
128
Location
NY
This is correct. I believe technically the one next to the thermostat housing, screws into the intake, has 2 prongs is a SENSOR. It only goes to the computer.

The one on the side, between cylinders one and three, screws into the head, is a SENDOR/SWITCH. It only goes to the dash and controls the temp gauge and the ‘check gages’ light.
 

name

OBS Enthusiast
Joined
Aug 9, 2019
Messages
81
Reaction score
41
Location
ohio
the one yhat you are holding looks like the sender that goes by the thermostat housing it tells the computer what temperature the engine is. The one you want is usually in the drivers side cylinder head and is a one wire hookup.

The one by the thermostat housing has a different pin configuration and the connector is a little smaller, they will not interchange ( plug in ) on my truck. Here are some pictures of the the one by the thermostat housing.
 

Attachments

  • IMG_0093.JPG
    IMG_0093.JPG
    172.5 KB · Views: 6
  • IMG_0094.JPG
    IMG_0094.JPG
    161.7 KB · Views: 6

name

OBS Enthusiast
Joined
Aug 9, 2019
Messages
81
Reaction score
41
Location
ohio
take the clear cover off the cluster and pull the needle off the temp gauge while the engine is up to temp and put the needle back on at the appropriate reading.


Is there another part that could be at fault besides the sender unit, I would hate to go threw all that and find out that I something else was the issue.
 

name

OBS Enthusiast
Joined
Aug 9, 2019
Messages
81
Reaction score
41
Location
ohio
when doing some research before posting , I came across some thread that was talking about the clutch for the fan being filled with to much hydraulic fluid, causing the fan to spin at a higher RPM witch in turn causes the truck to run cold.

I dismissed it as BS, But what do I know .

Just saying....
 
Top