OT: My truck's temperature gauge doesn't work.
The needle on the temperature gauge on my truck is always at the very bottom of the range. Stone cold.
The voltage at the wire that connects to the coolant temperature sensor reads 9.79 volts.
The resistance from the coolant temperature sensor to ground is 1040 Ohms when the engine is cold and 485 Ohms a couple of hours after I shut off the engine (the engine was still a little warm to the touch).
I'm guessing that the gauge went out but I thought I'd ask you guys since this is the first time I've ever diagnosed this type of problem.
What do you think the problem is? Do I need to do some more diagnosing?
My guess would not go to the guage first but rather the temperature sending unit which is probably screwed into the head, the water neck or possibly the intake? I am most experienced with GM products which generally sticks them in the head.
I would replace that first, then head for the guage if that does not fix it.
Be sure to check the thermostat. I thought the temp gauge on my F150 had died until the day it was about 100 outside and I was running the AC. That got the temp gauge to move slightly! It's a good thing the thermostat died while open.
I hate factory gauges. I put these in my Ranger plus a voltmeter.
I would suggest you find the engine sender unit , disconnect the wire from sender and leave the wire unhooked (open circuit), turn on ignition, and watch the guage. Then turn off the ignition and ground the wire to sender, turn on ignition and watch the guage again. The open circuit or the grounding of the circuit should produce a hot reading. If that happens the sender is probably bad. If neither test shows afull reading then the dash guage unit is probably at fault. JIM
Make sure you are checking the correct sending unit. My Chevy has a sending unit in the head that goes to the gauge and one in the intake that goes to the computer. Ditto the above post to ground the wire.
I already grounded the wire from the gauge at the sending unit end and the needle didn't budge. As I mentioned above the wire from the gauge has 9.79 volts at the sending unit. I have voltage.
Because the resistance at the sending unit (coolant temperature sensor) increased as the engine cooled I'm assuming the sending unit is operating correctly.
Since the gauge doesn't budge when the wire is grounded or when the wire has infinite resistance (disconnected from the sending unit) but it does have voltage is it correct to assume it's the gauge?
Can there be a voltage if the gauge somehow became disconnected?
How old is the truck, make, miles, etc.
My 1987 GMC 136,000 miles the gauge sticks on hot days, replaced the sender and now sometimes it sticks at the hot end when I turn the key tio ignition position. I usually pound on the top of the dash board and it then works. I was told by a mechanic friend that the gauge and sender have to be compatible as some after market stuff will give you faulty readings plus gauges vary from auto maker to automaker.
My Massy Ferguson farm tractor a 265 Diesel has the best idea as a brass/copper tube goes from the engine block straight into the back of the gauge, no dumb sending unit, simple is better.
Last edited by GRH; 08-18-2007 at 06:37 PM.
I suspect the dash guage is the problem. You say you have voltage at the sender ,which should eliminate any fuse problem. Not much left but the dash unit. JIM
Hang on a minute, last time I looked this was a MACHINIST site, so what in the blue blazes has a trucks water temperature gauge got to do with this site?
Come on now, get real, how in the heck can anybody diagnose this problem without being on the spot!
If you want this advice, go to an Auto Electrician and spend some money you bloody cheap skate and stop filling this site with absolute BULL$#!T!!