underheating

After a long trip about 350 mile, I stopped at a light and I notist my temp gauge is down to 150. Not seeng this before I pulled off of the road to investigate whats going on under the hood, As I did this the temp gauge moved back to 210. So I'm thinking now I'll be OK ? Right ? Or is this the start of a bigger problem ?

i would change the temp sender. they can go bad giving false readings. cheap any easy replacement.

I have a 97ZJ I bought last year, the previous owner mentioned bad gas milage, I noticed that the temp gauge never got above 150. I bought it and replaced the thermostat, it came out in 3 pieces so it was for sure 'stuck open' LOL...
Mileage more than doubled from about 8-9 to 21-22. Thermostat is pretty easy and alot cheaper then a sender is.

My 90 RENIX runs too cold in the winter, everything is good on the closed cooling system so i just block off the grill opening (during winter only of course!)