Temp Gauge Fluctuating

[CRocker]

For the last 250 miles of today's 325 mile RTE I watched the temp gauge on my '88 do something I haven't noticed before...

Normally, with temps like today's, it stays right at the bottom edge of the normal operating range (it would be pointing at the center of the Neutral Lamp) while riding on the highway.  Today, however, I noticed it climb from it's normal position (over the course of 10 seconds, or so) to about 20% of the normal operating range (where it would be pointed at the lower LH corner of the Headlight Lamp)...then, it would drop back down to it's normal position (over ten seconds, or so)...and this whole process would repeat over and over again. 

And, a couple of times, it remained at it's normal position for several miles at a stretch...

All riding was done on a 65mph two-lane highway at speeds of 60-75 mph...

I have included a picture of my instrument panel for reference...

Any ideas?

[Motor Head]

 Sounds like the Thermostat cycling, and your description of the Gauge where it points to, sounds like the open and closing temps for it. This fluctuation is normal, in cooler temps. That is if the system is full.
Have you ever done a cooling system flush, and replace the maybe original thermostat?
 The O-rings on the two coolant manifolds would also be a good idea, if not new hoses as well.

[CRocker]

Uhh...no...not in the 18 months I've owned it...

[Rick Hall]

I recall the first few years the Connie temp gauge 'hunted' during cold temps. The solution was to redesign the thermostat. Drill a small 'weep' hole in the rim.

Or partially block the airflow through the radiator in cold temps.

Rick

[Motor Head]

Uhh...no...not in the 18 months I've owned it...

Well if you go to do it, the valve cover comes out Much easier with the rear water manifold out of the way, or the Stat housing, you may want to check the valve adjustment. Then for a couple of bucks you could replace the 7mm ignition wire.
 
 As Rick Hall stated, you can put a small weep hole in the rim of the Stat. That is if the new one doesn't have a hole or jiggle pin. Somewhere there is a post about a Mod to make a bypass system. But basically if the Radiator takes a lot of cold air, the temp there will always be less than the Set temp of the Stat. So when it opens it gets a Gulp of chilly liquid, then it closes, just to do it over again. Partial blockage of the radiator surface will help, as Rick said, but in 40 degrees it is not really an issue.