Inacurrate temp sender

I bought a new temp sender for my dauntless. I tested my gauge and the voltage regulator is putting out a fluctuating 5-6 volts like it should. The temp gauge wouldn't peg when I grounded it, so I changed the temp gauge with one from a different speedo cluster I had laying around. Now both the fuel and temp gauge peg when I ground them.

When I start the dauntless, the temp gauge slowly climbs to the very end of the green line towards hot (it dosn't peg, it goes about 90 percent). I got a cooking thermometer for 7 bucks. Everyone should have one of these things. Its running at a perfect 195 and not fluctuating. Any ideas as to why my temp gauge almost pegs every time? My fuel gauge reads about empty but I only have about three gallons in there so I'm not suprised.

 

Shouldn't you run at the top edge of green at 195F? Doesn't green mean the temperature is ok?

 

just a shot in the dark here, but is it possible that the resistance is different for the gauge out of the other speedo?

 

I thought it should be somehere in the middle like my other jeep. With it at 90%, you have a hard time telling when your overheating.

I didn't think of that. I figured the resistance would be the same through all jeep years. Sounds like it's a logical explanation tho!

 

do you know what year etc the gauge you are using is? if so you may be able to find out by getting the sending unit for that year model, or see if it calls for a different part# you should be able to determine whats going on with a good ohm meter

 

After putting this together I feel like I need to apologize for at least the length and most likely way too much detail..............Sorry!

My old original Jeep Service Manual reads: "On some vehicles, the temperature guage may register on or close to the H (hot) mark when coolant tempature is 190 F to 200 F. In such cases a 25 ohm, 1 watt resistor may be installed on the temperature guage which will place the pointer just beyond the center mark at a coolant temperature of 190 F to 200 F. Install the resistor between the two terminals on the back of the guage. Insulate the exposed leads of the resistor with electrical tape."

Note: You will need to remove the metal strap, or possibly existing resistor, that is between the two terminals on the back of the guage. The metal strap is a dead short. The greater resistance you put between the two terminals the further toward Cold the needle will move.

When I had to install a new temp gauge a few years back I had the same situation you do. I found that the 25 ohm resistor wasn't exactly right for my new temp guage and existing sending unit combination. I tried different value resistors with the coolant at normal running temp until I found the one that put the needle near the center of the guage.

The easiest way to do this, after removing the metal strap, is to connect leads to the two terminals on the back of the guage so that you can connect a "Decade Resistor Box" or misc resistors to the leads to determine what resestance value you will need. A Decade Resistor Box usually had six variable switches, starting with 1 to 9 ohms for sw 1, 10 to 90 ohms for sw 2, etc. The switches can be adjusted until your guage reads where you want it to at normal operating temp. If a Decade Resistor Box is not available come up with a few resistors and see what works. Then just get a resistor, or 2 or 3 if necessary soldered together in series, with that ohm value, or close, and make sure it/they have at least a 1 watt capicity value. Greater capacity than 1 watt, such as 5 watt, 10 watt, etc, is OK. Anything less that 1 watt capacity and the resistor will probably fail due to over heating. I like to error on the side of "not having to do it again". I think I used a 5 watt resistor.

Make sure not to get the engine to normal operating temp and then shut it off to do this because the hot engine will heat up coolant past normal operating temp after it is shut down due to the engine being hot and NO cooled-down coolant being pumed through the engine from the radiator.

Good Luck!