My 87 Z28 has had all of the expected cooling problems over the years. A few weeks ago I swapped the carb, dist, & intake manifold out & went non-computer. While at it I put in a new radiator & thermostat either 160 or 170.

Now it seemed to never want to warm up going by the temp guage although it had plenty of warm air etc.

I went ahead & swapped out the thermostat as I had a small leak on the housing & couldn't get it to seal. Went with a 180 stat this time & the car finally does warm up going by the temp guage, although it doesn have warm air quickly.

Problem is when I hit the highway it immediately drops way down like it is cold. Could it be a bad stat which would have meant the first one was bad too. Don't recall the brand but went with a better one than the el cheapo route.

Could it be a bad tempt guage?

 

It wont warm up because you went with a cooler stat. Try going back to the stock 195 and see if that fixes it.