mechanical question (car)

[Lee]

Vehicle a 1990 Jeep with an older GM 350 motor.  There is a small coiled wire coming from the top of the thermostat housing and running to the dash.  I'm assuming this runs to the temperature gauge.  I can't find anything like this on Google.  What is this?  How does it work?

[Nick1911]

I don't know that vehicle well enough to tell you that this is what it is; but, assuming it isn't electronic, some manufactures actually make a temperature sensor that uses a working fluid inside a bulb, with a small hollow tube running to the gauge.  It's entirely non-electric.  As the bulb heats, the working fluid pressurizes, which is what moves the gauge movement. 

[Hawkmoon]

Small wonder you can't find anything, since 1990 Jeeps did not use GM engines. Whatever you have is a home-brewed engine swap patient.

If the wire runs to the thermostat housing, it is almost certainly connected to the temperature sensor. That is typically a variable resistor, in the ground leg of the circuit. 12 volts goes to the positive terminal of the gauge, then a wire runs from the negative terminal of the gauge to the sensor. If the instrument cluster is original, "wire" may include some printed circuit traces behind the gauges and then become wire at a connector where a wiring harness connects to the instrument cluster.

[wmenorr67]

^^^This.  How long have you had the Jeep?  Can you go back to the person you got it from and ask them?

[Tallpine]

How does it work?

Either well, or not at all.  So you tell us? 


No, I've never seen something like that on a GM 350, and I've had so many of those "older" ones that I've lost count now.

[Lee]

So essentially, it's a ground wire.  It was a 4 cyl. originally.  Someone put the 350 and TH 350 trans in it.  The gauges appear to be original though.  I don't know the who, when, where, why's of this Jeep.  The guy I bought it from only owned it 6 months, and he didn't make the mods. He liked it a lot and decided to buy a new one.  

[Brad Johnson]

Whatever you have is a home-brewed engine swap patient.

Small block Chevy conversion kits for Jeeps have been around for quite a while.  Some of them are darned good, well engineered and with very high quality parts.  Others, not so much.

Brad

[Lee]

Sorry, I'm having some connectivity issues today, so I'm about 3 replies behind. 
I left out the fact that it has an Edelbrock intake manifold.  The Thermostat housing has a brass fitting on top of it, and the coil comes out of the top of that.
It gauge seems to work OK, but I noticed that there was some antifreeze leaking right behind the housing (while sitting cold)...so I tightened the hose clamps, and that seems to have made it a little worse.  I cleaned it up the other day, and have a new wet spot today - I haven't driven it in a week.  I have no idea how old the hoses are, but they look old.   

[wmenorr67]

Change them.

[Lee]

  I will.  This isn't a regular driver...probably won't get out of the garage for a few months.   

[Brad Johnson]

I'd say it's likely high time to go one better than just changing the hoses.  You have a cooling system of unknown age and service history.  Go ahead and do a flush with fresh hoses and a new thermostat.

Brad

[Lee]

Yeah...that's probably a good idea. 

[Lee]

After looking a little closer at this gizmo...I think someone drilled and tapped the thermostat housing and installed some type of pressure switch or something.  Odd.