Temp gauge help...

[PNWEx]

So, on my way home from work my 94 explorer limited 4x4's temp gauge fell to c and stayed there. Once arriving home,the top radiator hose was hard and hot. I turned the truck off and the gauge moved to its normal position. When I cranked the truck up again it fell back to the C. Any ideas to what this could be? I was thinking the sending unit but it seems when I turn the truck off it reads fine.

 

[PNWEx]

Also, my heater blows hot. AC blows cold. Truck runs great. And I know it was working this morning.

 

[ChildIdenticant]

Regarding the sending unit, what do you mean by "when I turn the truck off it reads fine"?

 

[PNWEx]

Regarding the sending unit, what do you mean by "when I turn the truck off it reads fine"?

It will start to read about where the O is in normal. And as the engine cools itll drop down to its normal resting place.

 

[Josh P]

With the ignition off, take the wire off the coolant gauge sensor and ground it. Turn the ignition on, if the gauge reads hot, it is ok and the sensor is bad.

 

[LG57]

Be aware there are two temp sending units. One is for the temp gauge and the other is for the computer. Be sure to get the right one.

 

[PNWEx]

From what I've read in here I think my thermastat is stuck open. So I'll start there after doing the front brakes and rotors.

 

[Josh P]

From what I've read in here I think my thermastat is stuck open. So I'll start there after doing the front brakes and rotors.

If your thermostat was stuck open, your heater wouldn't work well, and you could hold onto the radiator hoses without burning yourself.

 

[PNWEx]

Could a bad head gasket cause the temp to read cold? I let the truck run for about ten minutes and I notice that the heat was blowing not hot but warm and the needle would barely move. But it remained between the C and the N.

My oil looks good. I am pretty sure that its the head gasket the upper radiator hose was still hot though. Could the thermostat be stuck half open?

 

[Josh P]

Are you losing any coolant? How often do you have to add? Do you keep track of your fuel economy? If the thermostat was stuck open, your engine would never get to 160 degrees, which would keep the engine in open loop.

 

[PNWEx]

Are you losing any coolant? How often do you have to add? Do you keep track of your fuel economy? If the thermostat was stuck open, your engine would never get to 160 degrees, which would keep the engine in open loop.

Not like an abnormal loss I wouldn't say. My fuel economy is pretty much the same.
But it just happened. My oil looks clean. And I noticed it after I was coming over the mountain I like on. But for 8 bucks I'll throw a new thermostat at it and see what happens.

 

[DaSovietPotato]

I would look at the wiring and sensors first as there is no positive indication that the thermostat is stuck open. A new sending unit only costs about $6 and can be more easily removed than the thermostat.

 

[PNWEx]

I think I am gonna replace both while I'm there.

 

[PNWEx]

So, on some of the other thermostat threads, people have mentioned having to drill a small hole for a relief. All of the ones I can find around me have what they are calling a jiggle pin? Is this the same thing? And if so, how does the jiggle pin work?

 

[Josh P]

The jiggle pin is similar to a one way check valve. When the engine is off and the water pump isn't creating any pressure, the pin falls out allowing any trapped air escape. Once the engine is restarted, the pressure from the water pump pushes the pin back in to seal. If the thermostat doesn't have a hole, I'll drill one and put that hole facing up.

 

[PNWEx]

The jiggle pin is similar to a one way check valve. When the engine is off and the water pump isn't creating any pressure, the pin falls out allowing any trapped air escape. Once the engine is restarted, the pressure from the water pump pushes the pin back in to seal. If the thermostat doesn't have a hole, I'll drill one and put that hole facing up.

Ok, yeah the the haynes manual says to put the air hole up and I cannot find on with an air hole just the jiggle pin

 

[Josh P]

Ok, yeah the the haynes manual says to put the air hole up and I cannot find on with an air hole just the jiggle pin

A 1/16 drill bit will create the vent hole. One with a pin is good too

 

[PNWEx]

A 1/16 drill bit will create the vent hole. One with a pin is good too

so the pin will do the same thing basically?

 

[PNWEx]

Also will a 198 degree thermostat work? I know that the OE motorcraft is labeled a 190 but may open at 198.

Pretty dang confusing...if ya ask me.

 

[Josh P]

so the pin will do the same thing basically?

Yes, it is similar. A 198 thermostat would work, you lose a few degrees of buffer on a hot day or steep hills. I realize Portland isn't extremely hot in the summer.