I'm suspecting a blown head gasket, but I don't know the engine temp because the temperature gauge on the instrument panel is swinging wildly from top to bottom, with a rare momentary stop at a believable temp reading. I don't know where the temp sensor is so lets start there and see if I can get reliable temp readings. Thanks, Jim

'89 Dodge Dakota, 3.9L

 

I think the sensor for the gauge is right next to the heater hose outlet on the intake manifold. (passenger side) It's a one-wire sensor, sounds like you have a bad connection.

 

To be specific, it's hidden under the A/C compressor, right behind the right (passenger) side front most intake bolt.

It's a 1 wire sending unit.

The insulation was cracking on mine.

RwP

 

Dodge must have rolled dice on each engine to decide which sensor to put where..... On the ones I have seen, it was the two wire sensor (for the pcm) that was stashed under the a/c compressor.

 

Yep; that's where it is on the Magnums. The LAs have it as I stated. Has to do with single plane vis kegger.

RwP

 

Thanks guys(?), It's a single wire under the compressor and it has bad insulation. The wild swinging went away when I moved it so it wasn't touching other wires or the manifold. Photos attached.

I have a lot of shrink tubing. I think I will cover it with that.

I'll let you know how the rest of the head gasket diagnosis goes. A good friend of mine has an automotive machine shop and he will do the head work for the cost of the gasket.

Sensor

Bare wire