1997 z-71 Cooling problem, changed thermostat but no water circulation. It got pretty hot when all this suddenly happened. truck starts and runs no white smoke.

start with a thermostat , do a good check of cooling system , are the cooking fans working properly , possible flush cooling system out.

it could be you have an air lock in the cooling system
remove the rad cap from the rad, start the engine and let it run until the coolant drops (add to fill it back up) or until the coolant boils out of the rad spout.

maybe pull the heat sensor. -replace it OR clean it off, reinstall it.

get a head gasket test done they may be bad and need replacing. it could be a bad water pump or poor cooling system circulation. is the rad cooling fan working like it should.

Probably the water pump. If the exhaust had issues, it would run.

Maybe a thermostat..or the heatercore clogged up..If the vehicle runs hot pretty quick then its the thermostat stuck closed..If the vehicle is not running hot,but you have no heat then the thermostat will be stuck open or the heater core not circulating

First when car is running hot stop and pop the hood check and see if the electric cooling fans are running. Second have your radiator cap checked, replace if bad. If neither or these are the issue, with the engine cold start it up and remove the radiator cap. It will take a couple minutes for the engine to warm up enough to open the thermostat. After it gets warm enough that your thermostat opens, (5 to 10 minutes) you should see the fluid in the radiator start to circulate. If this doesn't happen your water pump is out and needs to be replaced. Back to the first thing if your fans aren't kicking on check all your fuses in your engine compartment first. If you narrow down the problem to one of these and need more assistance, just reply to this comment and I will help you further.

1. Improper water circulation: Sometimes, eventhough you are sure that you have enough water on your radiator, your car still overheats. It might probably be that the water is cannot circulate properly, which results to improper cooling process. There are several reasons for this which you can discover by yourself. To verify if the water circulates properly, start your engine without the radiator cap. If water circulation is good, you should notice that the water pops smoothly over the top but still retains the amount. Another way to check, detach one of the ends of your radiator hose from your radiator and see if water flows continously over.
If water doesn’t circulates well, check the thermostat if it’s open. It should be open, meaning clean, and the water can pass through it.
If thermostat is clean and still the water doesn’t circulate properly, then you have to check the water pump. That’s probably where the problem is. A little leak on the pump will cause improper flow of water through the radiator system.
If you are sure that the problem is not about water circulation, another thing you can consider is check the engine oil. Very low amount of oil can cause greater friction of the mechanical system of your engine. If it’s not time to change oil yet, you can add over some amount of oil until advisable amount is reached.
While we can’t be always sure about our engine, especially if it’s not new, we should be prepared when it happens. Bringing extra gallon of water in your trunk will surely help.

check the water level in the radiator and in the expasion tank,
I reckon the thermostat has failed (very very likely).
http://auto.howstuffworks.com/cooling-system8.htm

when it fails it never opens to circulate water to the radiator, if this is true your temp gauge will read HOT but the radiator will be quite cool compared to the engine. ------ Thermostat is around $60 / £48 from BMW only!!, a non-bmw part is false economy and will invalidate your warranty.

Run the engine and look at the header tank , is there lots of air bubbles coming back out of the water if is then the head gasket may have split and that is down to either a can of Radweld or a strip down repair

If the radiator is not uniformly hot them I would go for that as your problem

Normal operation is that the engine starts the thermostat is closed , engine block heats up and opens water starts to circulate around the block

So to check that you need to fill the radiator with cold water run it for a few minutes check the bottom hose it should be cold

The stat opens and the bottom hose should get hot as the water from the block is pumped into the radiator for cooling.

The radiator should get hot all over and the cooling fan should kick in when the sensor hits the over limit stop.

If that does not happen then get someone to remove the stat altogether (It is only there to get the engine block warm quickly in cold regions )

In which case the bottom hose should go from cold to warm to hot

does it run hot while driving or in traffic?
if running hot at idle could be water pump not circulating enough try revving engine some and see if temp comes down. also check your fan clutch.
if running hot going down road probably radiator