temperature gauge readings 66 CJ5

I'm trying to get everything original working correctly in my 66CJ5 with f134 engine. I just installed a used but original configuration temp gauge in my instrument cluster and a new sending unit . Before then I was using a manual SW temp gauge under the dashdash which let me know the engine operates at 185-190 under normal conditions and its never overheated. However with the electronic gauge in the cluster, I'm getting a reading of 3/4 deflection which is about halfway between mid point and hot. I checked the resistance between the terminals on the gauge and get 12.5ohms, I think it's supposed to be higher 19-21 ohms. Otherwise the gauge responds to temp changes as it should. Two questions.
1) would the low ohm readings mean the gauge is not working accurately
2) Do I need to replace the gauge or can you install a resistor in line to calibrate the reading to a mid point at normal temp?

Eddy

 

Thanks,
No I did not disconect the TSU. I will do that and retest the resistance between the terminals. Great suggestion. And I did a search yesterday and read the string you sent. It makes me wonder if I have the right TSU.

I changed the 180 thermostat yesterday and put in a 160 but it only made about a needle width reduction in the reading. The 180 was the original thermostat and had a date stamp 7/65 on it. It looked like new but different than the aftermarket ones.

Thanks for your suggestions
Eddy

 

Mine does the same thing , if you find the problem please post. I never bothered to find the problem and fix mine .

 

Will do,
I'm going to see if I can find a 10 ohm resistor and put it in line between the gauge and TSU just to see what it does.
Eddy

 

Re: Calibrating temperature gauge readings 66 CJ5

OK, I found you can calibrate the guage and sending unit by adding a resistor in line. I picked up a 10ohm resitor from Radio Shack and installed it in line at the end of the wire on the sending unit and it dropped the needle deflection towards C which was the direction I needed.

Before the resistor and at 160F, the stock guage was registering about 2 needle widths above mid point on the guage (towards H). After the 10ohm resistor, it is about 2 needle widths below mid point towards C. I think a 5ohm reistor would be about right and I'm looking for one now.

Eddy

After lunch update:
I couldn't find a 5ohm resistor but an engineering friend explained that if you connect 2 10ohm resistors in paralell you get 5ohm. According to my meter, he was right and 5 ohms resistor in line just before the TSU calibrated my guage exactly to mid point with 160F thermostat.

Sparky, this may be worth logging somewhere.
Eddy

 

glad it worked for you!

 

eddy, as i mentioned earlier a trim pot would work also. a trim pot (or trimmer potentiometer) is just an variable resistor which has a similar form as a volume control on an amplifier or radio.

trim pot definition

there are lots of forms of these:

trim pot samples


a trim pot tends to be smaller and have a stem on it slotted for a screwdriver and a lock nut. you adjust the screw control until the value of the resistor (potentiometer) is correct or the needle is aligned correctly. that way you don't have to worry about finding a regular resistor of exactly the right value. just find a pot that contains the value within its range and turn the screw until the gauge meter is lined up with exactly what you want.

the drawback is that some trim potentiometers may not be weather and vibration "proof".