Temperature gauge is out of control

[chris142]

I know stock gauges suck but its all I have right now. Got too many other things on my mind to install a good gauge.

It goes from M on normal to the L and back constantly. About every mile or so. I changed the sender and its not the problem.

What else could be causing this? Bad gauge in the dash?

My infrared temp gun shows its not running that hot.

 

[BrianX128]

Bad ground? Sounds like a frayed connection somewhere. I had an oil pressure sender that did the exact same thing and the push connector for the wire on the sender wasn't "tight" and I'm almost positive wind through the engine bay was causing it to fluctuate.

I smushed the end of the push connector with pliers and put it back on the sender tight and the oil pressure never moved from the r in normal since. Aftermarket oil pressure gauge never has shown any different oil pressure during that whole fiasco that fluctuated like the dumb factory gauge was either.

 

[snicklas]

One other thing to remember on the oil pressure gauge. From 87 on (I know on my 03 6.0 and my 07 4.6 P71) it is not a gauge, but more of an idiot light. The sender is a switch, that at approximately 7psi causes the needle to move to the "middle" of the gauge. This setup will NEVER show any change oil pressure, unless it drops below 7psi....... so the gauge moving around HAS to be 100% electrical....... I agree with Brian, look at connectors, and check all your grounds.....

In my 2000 P71 at idle in drive, with any other electrical load (light on, blower on, etc) the oil pressure needle would swing so fast it would literally bang off both ends of the scale, and occasionally it would just drop to the low end and stay there, like it had no pressure. Touch the throttle, put it in neutral, it would work fine. There was no ticking or knocking from the engine as though it had no oil pressure. I read up on the issue, and ended up putting a dedicated ground wire from a bolt on the alternator that also went into the block, to the negative post of the battery. Almost all the strange electrical issues with that car cleared up........

 

[CDX825]

The instrument cluster has a voltage regulator on it. When they start crapping out your temp and oil pressure gauges will act weird.

 

[Shadetreemechanic]

I believe you actually have two senders in this model, one for the guage and an overtemp sender. The overtemp is an on off sender that should turn on the engine light and max out the temp guage when it hits a preset temp.
You might look for that sender and disconnect it and see if that helps. I don't known exactly where to find it on the motor, but others may chime in. Search function here should give you location as well.

 

[snicklas]

The instrument cluster has a voltage regulator on it. When they start crapping out your temp and oil pressure gauges will act weird.

86 and under. They went away from the IVR with the bricknose trucks.... I've played that game also. However, the 86 and under, the gauge does actually show pressure differences, as it is a sender, not a switch....

 

[BR3]

I had similar trouble to the op a while back in my obs idi. Contrary to what 99% of people (I don't blame them, that's basically what everyone says) the coolant temperature sensors is actually that, a sensor. There is the idiot light, but the one on the dash actually works if it is functioning properly. It's a resistance based thermistor that REDUCES resistance as your temperature goes up.

That has several implications. In my case, when I upgraded my electrical system with bigger wires, more grounds, and better battery's, my stick coolant temp pretty much pegged high at a real 190, due to the fact that I had decreased whole truck resistance. The cluster is supposed to be able to handle this,but after 20 years I guess it had enough.

My simple solution outside of removing and rebuilding the gauge cluster was to find a common coolant temp thermistor chart online, and make some basics caluclations based on engine temp and displayed temp, and wire in a what in my case was 73ohm resistor. Now it's right back where it should be and functions great.
Hope that helps.

 

[chris142]

My 87 has a working oil pressure gauge. It shows low @ idle and moves up with oil presssure.

Is there any kind of voltage regulator I can replace for my dash?