Coolant temp not registering on gauge.

I have a 93 Blazer, 4.3 W engine. This vehicle has the digital dash, when I first got it, the temp gauge didn't register (lights up full with key to display that all bars are working). Shortly after having it awhile, the gauge started to register, but it was on the lower end, no where near normal operating temperature. The next couple of drives it didn’t register anymore, than the next couple of drives, it registered and on one of those drives, it was registering normal temps for this engine. No it is back to not registering at all.

Does this sound like a stuck thermostat (went for an 80 mile drive last night and it never did register, heater is plenty warm), or is it the digital dash or possible the temp sending unit?

With the vehicle cold this morning, I took the Rad cap off and started the vehicle. Radiator was full, under acceleration it would dip the level a bit until I let off, then go back to full to the cap once again.

Any ideas?

As far as the digital dash goes, the only lights that are out on it are the yellow/red tach lights, which I understand to be fairly common.

There is no engine light, but I'm heading to O'Reilly's to plug in their scanner.

More than likely it's the sending unit on the drivers side block. Replace that and it should be fine.

My temp sending unit for the gauge is on the passenger side between the first two plugs. Fortunately, that took care of my problem. There is a sending unit of some sort on the drivers side between the 2 and 3 plug, anyone know what this is?

The coolant temp unit for the ECM is located in the front of the manifiold.

I'd really like to know what that unit is on the drivers side. O'Reilly could'nt tell me, and I don't have any sort of manual.

Ahh, I forgot 92-94 put theirs on the passenger side, the unit on the drivers side is the driver's side knock sensor, the other one is behind the passenger side head.

Thanks for the info. The wire harness plug for the knock sensor appears to be deteriorated something fierce.