Bad temp Gauge? Good heat.

[wyyup]

Hello everyone,

1992 Ranger 3.0. The temp gauge fluctuates quite a bit in this range:

I would expect if it was running cool, I wouldn't have heat. However, the heat is working very good and hot. This morning, the temp made it to the 'O' in "Normal" and it stayed there for 15 miles until I stopped to get gas. Once I turned it back on, it started jumping around again and wouldn't stay in the normal range.

Could this be a thermostat stuck open or just a bad temp sending unit?

thanks!

 

[RonD]

If heater temp stays constant then t-stat is working fine.

You can test the gauge easily and then replace sending unit if wire and gauge pass the test.

Find the ONE WIRE sending unit on the engine, there are two temp sensing devices, a two wire sensor for the computer and a ONE WIRE sender for the gauge.

Remove the one wire connector from the sender
Turn on key
Temp gauge needle should go all the way down or all the way up
Use a short wire and ground that one wire connector
Temp gauge needle should do the opposite of above, all the way up or all the way down
Turn key off

If needle has full range then wire and gauge are working fine, replace sender
If needle does not have full range then wire from sender or gauge has a problem.


If you replace sender, remember that all 1 wire senders need their threads as a ground, so NO SEALING TAPE on the bottom few threads, sender needs a good ground to work.

 

[ab_slack]

I usually find I get decent heat as soon as it moves off the bottom of the gauge. I partially depends on how cold out it is if your heat is good or not.

Don't forget to check fluid level as low can cause low temp readings sometimes if coolant is getting where the sensor is.

 

[kohlbeezy]

im resurecting this thread. i am having similar issues. when the one wire connector is connected to the sender it goes past the H on the gauge. when i disconnect it, it goes to the C or below. just replaced the sender. am i missing something?

 

[Rearanger]

when the one wire connector is connected to the sender it goes past the H on the gauge.

Engine cold?

when i disconnect it, it goes to the C or below.

I think RonD was giving both possibilities depending on polarity of the gauge. I understand the standard test is if wire to sender is grounded (key on) gauge will peg at "H", which proves the gauge.

If you just replaced the sender and the gauge goes to "H" when wire is connected you have a short in the gauge or in the wiring. The sender is variable resistance depending on heat.