Temp light stays on constantly

[buffle]

Started my 87 today, and after driving about 10 minutes the hot light came on. Now it won`t go out, I guess I`ll change coolant sensor. Also put in new thermostat last week and upper hose doesn`t get hot. It is a stant stat. I always thought they were good stuff.

[geezer#99]

Did you put the stat in in the right direction?

[C-10 simplex]

It would be interesting to put a temp gauge on it as well to see exactly how hot, if it at all, it is.

[clinebarger]

Your temp sender wire is shorted to ground somewhere......It would take about 10 minutes for the exhaust manifold to burn through the insulation Make sure the wire isnt touching the exhaust manifold.

[bilfman]

Originally Posted by clinebarger

Your temp sender wire is shorted to ground somewhere......It would take about 10 minutes for the exhaust manifold to burn through the insulation Make sure the wire isnt touching the exhaust manifold.

As mentioned it might be grounded out. Could also be a bad sending unit. The best way to start the diagnosis is to let the truck cool right down for a few hours and start it up. If the light is off, it is most probably not a grounded wire and then could be a bad stat install.

If it is on the the sending unit is bad or the wire hooked to is is grounded somewhere. To check this pull the wire off the sending unit, if the light is on then the wire is grounded somewhere, if it goes off then the sending unit is bad.

[buffle]

Yeah the thermostat is in right. the light came on after my 1st trip on the road. I have started it in the shop a few times and it seemed fine. I guess I`ll unplug the sensor and see what it does and while the coolant is down I`ll drill a small hole in thermostat in case the problem is trapped air.

[buffle]

Are there 2 coolant sensors? The one next to the thermostat housing keeps engine from starting when unplugged. Is there another one that feeds the idiot light? It is a 4.3 V-6