Temerature sensor

Temperature gauge in 70 challenger hardly gets off cold. . the sensor when it is cold it reads 474 ohms. does anyone have a chart as what ohms it should read at different temperature.
thanks
Gregg

I don't have the answer to your question. But if you ground the lead to sensor and gauge sweeps to full hot, gauge is good.

^^^ do that & also you might ground the body (not the threaded shank) to a nearby ground (best would be to go all the way to the batt neg post) & see if it straightens out.

If I ground the wire the gauge is moving. Drove it around this morning for about a hour and gauge just got to C . . took heat gun and check temp of water pump where it bolts to block and it was only 174. When I rebuilt engine I sent radiator to Ray's and he put a third row veins in. Maybe engine not hot enough to move gauge that much . .

What thermostat are you using?

Is there any pipe dope or Teflon tape on the sender going into the water pump housing or intake manifold on SB ?
If so remove the sender and clean all that goop off of it and inside the threads on the where it goes and see if that makes it read better

1. Wrong or bad sending unit.
2. Bad ground on sending unit.
3. Wiring issue.
4. Guage needs to be calibrated.

Have a radio shack nearby ??

You can check the gauge and wiring with 3 resistors jumpered between the sending unit wire and ground.

10 ohms of resistance should read near high
30 ohms should be about mid point
80 ohms should read Cold

When doing the above test allow the gauge to stabilize for about 2 or so minutes

So if sending unit reads 474 cold on bench it probably the wrong sensor ? ?

These cars normally ran a 195 degree stat so "normal" should be around 200 degrees. I do not know OHM specs on the senders, but sounds like you are running cool. A simple mechanical temp gauge, installed temporarily, would tell.

Possibly, one would need the resistance spec's for that particular sender though. Your question did give me another thought,
One could warm the motor up to operating temp and take a resistance reading on the sender. knowing that 30 ohms should be about mid point on the gauge it might give an indication of whether the sending unit is the culprit. The best approach though is doing the resistor test previously mentioned.

I was going to install a mechanical gauge put could not get pipe plug out of water jacket housing. Next time I drive car I will check resistance when up to temperature. I wrote to auto gauge today to see if sensors come in different ranges of resistance . . .

You still haven't said what temperature thermostat you are running. It makes a difference.

180

Took car for a drive today .. temp by water pump housing was 175.
Ohm from sending unit was 60. Gauge inside was on the cold line. when car is 1st started the gauge is below the cold line can the needle be adjusted to start on cold line ? ?

FWIW, my gauge runs on the cold line with 180 stat. Based on the EFI probe, my stat actually opens around 175. Anyhow, I got used to it.

My understanding, the gauge can be adjusted after removing the cluster... though I have never tried it.

with a confirmed temp reading I would want an actual 180 water temp at a bare minimum. someone said something about some duct tape needed on shiny surfaces for a correct IR gun reading (not my area just a FYI). yes some gauges can be adjusted, look in the back side of it.

Sure but it will then be no longer calibrated

is this a new sensor or used one ? i have found that over time, deposits may build up on the sensor bulb making it look dirty or greenish in color, and causing the gage readings to be off. using a wire brush mounted in a drill motor removes the deposits, returning the sensor bulb back to a shiny, brass color, and readings return to normal due to increased conductivity to the sensor bulb. another "dirty connection" problem often overlooked. this might be something to consider. just my experience.

New Sensor put not sure where I bought it. I will look for a 40 ohm resistor and see see if gauge goes 1/2 way and go from there.

Have a radio shack nearby ??

You can check the gauge and wiring with 3 resistors jumpered between the sending unit wire and ground.

10 ohms of resistance should read near high
30 ohms should be about mid point
80 ohms should read Cold

When doing the above test allow the gauge to stabilize for about 2 or so minutes

I believe all radio shacks in Ohio closed. I did find a 39 ohm at work last night so I will test gauge today.

Be aware that the gauge response to resistance is not linear so using the 39 ohm will not tell you much about the calibration or potential circuit problems.

With 39 ohms the gauge came up to the cold white band. Where it goes when engine is around 175.