1996 Chevy Lumina Not overheating but running hot

It could be several things: old/low coolant, sticky thermostat, water pump going bad, radiator/water jackets getting clogged, cooling fan not working, loose serpentine belt, bad hoses etc.
Start by making sure your coolant is at proper level and in good condition (you can buy a coolant tester for $2 at Wal-Mart). If the level is low, add proper coolant to your radiator (engine cold!) And your overflow tank. If coolant too old, have your cooling system serviced (new coolant, radiator flushed etc)
Also make sure your fans come on when your car starts to get hot: open the hood; when the temp gauge starts to go beyond the middle, check that the fan located right in front of the radiator comes on. If it doesn't you have your problem.
If both the coolant and the fans check ok, I suggest you just go ahead and replace the thermostat; a new one only cost $5 and even though it may not be the culprit today, it may save you some problems in the future.
If it still fails to fix your problem, we still have a few suspects on the list: water pump, loose serpentine belt (either the belt has stretched or the belt tensioned is worn), bad hoses, an internal engine leak.

Start by checking your coolant and your cooling fan. Post back if you need more help.

No problem.
If your coolant was low you could have a leak somewhere, in which case it's only a matter of time before your car starts overheating again. You may want to inspect it visually (or have it inspected): check the hoses, the radiator, the water pump, around the intake manifold, the thermostat housing.
If there is no visible leak, have the system pressure tested; it will tell you if you have an internal leak. You may also want to have the radiator cap pressure tested. If the cap is old it may no withstand the 13-15 psi of pressure and leak coolant. If you still have the original cap, you may want to simply replace it ($5 at your autopart store).
You're doing the right thing by replacing your thermostat.
Let me know if you need more help.

Hello there,

150-160F is not normal operating temperature. Your engine should be running between about 195-210 (close to or at the middle of your temp gauge). Your thermostat is calibrated to open at 192-195 F.
I would start by replacing the thermostat; it sounds like it could be stuck open. Quick question: when you turn the heat on while driving, does it put out really warm air or just luke warm/cold air?

Let me know how that goes.

Again 150-160 is not normal operating temperature. The fact that your gauge shows 150-160 doesn't mean it is the actual temperature though. It's possible that your engine runs at normal temperature (around 195F) but your coolant sensor could be bad, or your gauge itself could be off resulting in the gauge showing only 150. You could find out by using an infrared thermometer and checking the coolant temperature at the thermostat housing, (engine idling at " œnormal' temperature) and comparing the temp on the thermometer to the temp on the temp gauge. You can buy this type of thermometer for $35-40 for the cheapest ones. You could also troubleshoot your coolant sensor by checking its resistance.
Since you said you were going to replace the thermostat, let's do it and see what happens.
If you feel like tackling this yourself, it's not a difficult job. All you need is basic tools (wrench, sockets, open wrench, a drain pan), and a Haynes/Chilton manual.
Quick tip: There's one way you can confirm a thermostat is stuck open: turn on your car when the engine is cold; grab the upper radiator hose with your hand; if you can feel liquid flowing thru it right away, it indicates a bad thermostat. It's not a very accurate test because " œfeeling' thru that thick hose while the whole engine is vibrating can be a little hard, but it may help you to confirm a bad thermostat nonetheless.

No problem.

If you need estimates on car repairs, here is a website for you:
repairpal. Com

Good luck