Normal operating temp

[4WDKC]

since our gauges dont have numbers what position does the temp gauge sit while driving down the road?

 

[77 K20]

The normal for the trucks I've owned and my dad's truck was 1/4 on the gauge.

 

[HotRodPC]

Depends on the year model. Some are #'s. Mine rides a couple needle widths below 210 with a 180 degree thermostat. In hot weather it'll ride at 210 so I think my gauge might read a bit high. Maybe not, it's a big block and they tend to run warmer, and they'll run a bit hotter using the temp sender in the head than in the intake manifold.

 

[4WDKC]

this is what my gauge looks like.

You must be registered for see images attach

and the needle never goes past that mark between c and 1/2

 

[MikeB]

My 69 pickup had a similar problem where the needle was at 1/3 full scale at 185 degrees or so. I replaced the wire wound calibration resistor on the back of the gauge with one of another value from Radio Shack. The needle then pointed straight up at the same temp. I don't know for sure, but 73-87 trucks may also have a replaceable calibration resistor.

Lots of good info here:
http://forum.73-87chevytrucks.com/smforum/index.php?topic=25339.0

An excerpt from the link:

COOLANT TEMPERATURE GAUGE PARAMETERS

For Truck Years: 1967 - 1973

The Temp Gauge Needle Should Point to:
Left Line (Cold) when sender resistance = 350 Ω
Middle Line when sender resistance = 76 Ω
Right Line (Hot) when sender resistance = 51 Ω

For Truck Years: 1974 - 1978

The Temp Gauge Needle Should Point to:
Left Line (Cold) when sender resistance = 350 Ω
Middle Line when sender resistance = 68 Ω
Right Line (Hot) when sender resistance = 46 Ω

For Truck Years: 1979 - 1990

The Temp Gauge Needle Should Point to:
Left Line (Cold) when sender resistance = 1,365 Ω
Middle Line when sender resistance = 96 Ω
Right Line (Hot) when sender resistance = 55 Ω

 

[77 K20]

this is what my gauge looks like.

You must be registered for see images attach

and the needle never goes past that mark between c and 1/2

That is the gauge I have. 1/4... or that little mark between C and the 1/2 mark was where mine and my dad's run at.

 

[4WDKC]

My 69 pickup had a similar problem where the needle was at 1/3 full scale at 185 degrees or so. I replaced the wire wound calibration resistor on the back of the gauge with one of another value from Radio Shack. The needle then pointed straight up at the same temp. I don't know for sure, but 73-87 trucks may also have a replaceable calibration resistor.

Lots of good info here:
http://forum.73-87chevytrucks.com/smforum/index.php?topic=25339.0

An excerpt from the link:

COOLANT TEMPERATURE GAUGE PARAMETERS

For Truck Years: 1967 - 1973

The Temp Gauge Needle Should Point to:
Left Line (Cold) when sender resistance = 350 Ω
Middle Line when sender resistance = 76 Ω
Right Line (Hot) when sender resistance = 51 Ω

For Truck Years: 1974 - 1978

The Temp Gauge Needle Should Point to:
Left Line (Cold) when sender resistance = 350 Ω
Middle Line when sender resistance = 68 Ω
Right Line (Hot) when sender resistance = 46 Ω

For Truck Years: 1979 - 1990

The Temp Gauge Needle Should Point to:
Left Line (Cold) when sender resistance = 1,365 Ω
Middle Line when sender resistance = 96 Ω
Right Line (Hot) when sender resistance = 55 Ω

not worried so much about the location of the needle, just what it is trying to tell me. If that mark indicates 150* then my ecm is going to let the engine continue to run rich because it not getting up to operating temp.

That is the gauge I have. 1/4... or that little mark between C and the 1/2 mark was where mine and my dad's run at.

Thanks.

 

[Georgeb]

The ecm reads off of a different sender in the intake manifold on the 87 TBI if you are going to need to verify what temp it's really running at. then you can verify the operation of both senders.

 

[4WDKC]

I was more wondering if the tstat in it is working correctly. without numbers on the gauge I had no useable information.

 

[HotRodPC]

this is what my gauge looks like.

You must be registered for see images attach

and the needle never goes past that mark between c and 1/2

Same gauge as mine except mine has #'s above the first, middle and last mark. Straight up is 210. After replacing my water pump, and fixing my heater hose leak, and paying more attention to mine since you posted this thread, mine actually stays just past the 1/4 or first mark off the C. If I sit in traffic or let it idle awhile, it's just below the straight up mark. So whoever said the 1/4 mark is probably right.

 

[MikeB]

not worried so much about the location of the needle, just what it is trying to tell me. If that mark indicates 150* then my ecm is going to let the engine continue to run rich because it not getting up to operating temp.



Thanks.

The only thing I can think of is to temporarily install a mechanical gauge in whatever coolant port you have available -- intake manifold, or one of the cylinder heads.

You can check the mechanical gauge for accuracy in a pan of hot water. I'd focus on 160 to 210. The best way to do it is to compare it to an air conditioning thermometer such as this:

You must be registered for see images attach

Ideally you'd have the gauge in the cab so you can "calibrate" your stock gauge while the truck is on the road and the temp is increasing. In my experience, differences between temp readings at the various ports are greater at idle, but less at higher RPM and when the truck is moving.

BTW, "calibrate" doesn't always mean "adjust". In this instance it means making a note of where the stock gauge needle points at various coolant temperatures displayed by the mechanical gauge. And that's exactly your goal.