Problem Solved:: Temp gauge flucuation

[NCali]

trouble with my temp gauge and yes I have read the gauge repair thread. The gauge goes from cold (as the truck heats up) all the way to 260 deg and then it will slowly go down to about the center of the gauge. as I drive the gauge goes up in temp as I go faster , let off the gas and the gauge goes down. I replaced the sending unit and it still does the same thing.
Anyone have the same type of trouble with theirs?

this is an 87 2wd 1/2 ton

[Irish_Alley]

when it goes up with speed does it go down just as fast

[NCali]

No it actually rises quicker .

[Irish_Alley]

wonder if thermostat is stuck closed. hows it act when warm at idle

[NCali]

I changed the thermostat just to see if it was sticking and it still acts the same way. The truck isnt overheating.

[bd]

Post a pic of the heater hose routing, including where the hoses attach to the engine.

[bd]

Does the heater blow hot air?

[NCali]

The Heater hoses are routed from the water pump to the heater core and return into the radiator tank at the top on the fill side.

Yes the heater works fine . when heated up it blows 100 degree air out the vents

I have a big radiator in the truck. It is a 4 core brass radiator
With the radiator cap OFF looking into the fill hole the water level is just below the heater return.

Watching the water from a cold start, water flows from the heater return line . As it heats up the thermostat opens and the water level begins to rise to the neck level and goes back down to just below the heater return . It will run like that until you put the cap on.
  There are no bubbles in the water (combustion gases) and it doesnt use any water (like a bad head gasket)  the truck doesnt overheat
  During that time, with the cap off the temp gauge works normally, put the cap on and drive it and the gauge fluctuates . Driving at 70 mph the gauge will go to the hot side of the gauge , then back to the center of the gauge where the truck always ran its normal temp
   When it is on the high side of the gauge driving 70 mph and I let off of the gas the gauge will drop back to normal

[FlatBlack77]

when you are driving at 70 and the gauge is acting up, how cold is it outside?

[NCali]

Problem Solved::  On the back of the Dash one of the lines (trace) on the circuit[ panel was broken so there was an open ground on the circuit panel

I scraped the plastic coating back and dropped a drop of solder on the copper foil. I felt lucky that it stuck to the foil but my gauges all work correctly. My dang speedo still bounces though