'84 240Ti temp gauge erratic

I'd put my money on the ol' degrading wiring harness. Check the harness right at the firewall, I'll bet that your wires are bare and the temp guage one is grounding out. Same thing happened to mine...

Bill

My '92 was doing that exact thing, and I flushed it, replaced the thermostat, and the temp sending unit. ANd the hoses too I guess. That cured the problem. I'm guessing it was the sending unit that was bad on mine (and yours)... but mine was due for a cooling sytem overhaul anyway so I shotgunned it.

-jeff

It's under the intake manifold, in the middle of the cylinder head, just above the block. It's got a single yellow wire going to it, and that insulation likes to fall off. Check the integrity of the insulation at the sensor, and near all the 8 pin plugs up on the firewall.

Do this with the ignition turned off. Take the wire of the temperature sensor (which is fitted at the engine) and measure the resistance between the wire and earth (the chassis). I'm not completely sure about this but don't think it should read anything (no connection between the wire and earth).

If it does, check the wire along its path into the cabin. On some cars the heat from the engine makes the insulation on the wires cracky so it falls off so the temp. wire gets in contact with earth. I don't know if the wire is exposed to heat on a 240, but you should check that.

Also check the resistance on the temp. sensor itself by measuring between it's connector and earth. It should probably be far above 20 ohm if the engine is not very warm (Volvo 140's temp. sensor uses this range so maybe it's the same on 240). Higher temp. means lesser resistance in the temp. sensor.

I believe that's it.

The wires at the firewall are all almost bare.

I will tape them to see if temporary relief can be found.

Now the oil light is on, blinks a bit, but the oil is fine.

So what does this mean---that the car needs a whole new wiring harness?

Allan

The short answer is yes. The longer answer is that you can buy the appropriate end connectors and piggy-back onto the existing loom and avoid the several hundred dollar expense if replacing the harness would be a significant portion of the value of the car.

Bill