Coolant temp gauge staying below operating temp?

[SuperZ5]

As the title says, I cannot get my 85 300z base to show that it's running at operating temp. After letting the car warm up (I would assume) the needle moves to about 1/4 of the gauge and will not get any warmer no matter what. I have replaced the sender with a new one from autozone, I have flushed and burped the coolant, and if I ground out the temp sender wire the gauge reads max hot. I'm so stumped some one please help me out lol I've only had the car for 4 days now and I'm afraid to drive it without a proper working temp gauge.

[SuperZ5]

Oh and I've also replaced the thermostat.

[BadQ45t]

Sorry nobody responded, I wouldn't worry about the car overheating, there is an idiot light that I have only seen 1 time in 38 years of ownership and that waas when the radiator plug blew out on the freeway, even on the 122 degree day in Phoenix I only saw the gauge move up (had to core that radiator at only 50K). I have never heard of this on a Z but saw on my friends Celica years ago. Maybe time to spend a little $$ and have a mechanic that looks at cooling systems everyday to evaluate.

[Great White Zed]

I have the exact same problem and, like you, made what I thought would be the necessary changes to fix things. No luck. So, when I get a chance (which may not be til Spring), I plan to extract the gauge and attach it to a battery. If it reads 0 then it's the gauge; if it maxs out it's gotta be a wire.