Jumpy Temperature Gauge Questions

[shertex]

The temp gauge on my 95 E300D jumps around a bit. Usually sits in the 85-90 range, will climb to 100, but will also move rapidly at times, both up and down.

My assumption is that very rapid movements of the gauge cannot reflect rapid changes in temp....that the thermodynamics of the system simply wouldn't work that way. Is this correct?

From what I've read, it's likely a bad sender or a bad ground. Any other possibilities?

How to I locate and access the sender?

Thanks.

[Jack None]

My gauge can get a little twitchy, but only when it's slightly above 100 C. I figured it might have something to do with water above boiling point. The system is pretty well pressurized, though, the water in the reservoir will only start boiling if it's above 100 C and I open the reservoir cap (with a rag).

These fast subsecond twitches can't be thermodynamic. The fastest real changes I've seen are maybe from 100 to 90 over 30 seconds or so when coasting down a hill.

BTW, operating at 100 C is a new thing for me. It used to run more like 90 C (mild summer day, 75 mph). Haven't figured out the problem (if there is one) yet.