My 1994 chevrolet 2500 6.5 diesel water temp does not work changed temp sensor and thermostat not overheating ?

Your list is missing the water pump. I'd also check belt tension.

You may have a faulty thermostat. Probable stuck in an opened position.

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Generally speaking, if it's turning, it's working. Although on rare occasions the impeller can erode, it is very rare. If you bring the car up to temp with the radiator cap off, when the thermostat opens the coolant should start flowing through the radiator. However, if there is an internal problem (like a head gasket), or the radiator is clogged, or there is still air in the system, it may belch out when it comes up to temp, so be careful. You may also check to see that the cooling fans are working if it only overheats while sitting still, I had a 626 with that problem. Let me know how it goes.

how recently have you changed the fuel filters?have other people used the truck?have you tried a commercial diesel fuel additive(power service) to help eliminate the algae that can grow if unchecked,with a diesel it usually amounts to a fuel or air issue so start by checking these areas,don't forget the air filter needs changed at regular intervals and fuel filters are the last line of defense on a diesel vehicles and water and algae are the enemy.
hope this helps.    

make sure that first the anti freeze level is correct. Then check the temputer sensor-fan might be cutting out if sensor is miss reading.1. temp sensor 2. fan

Sounds like you need a temp sensor for the gage. There's 2 under the hood one is a 2 wire in the intake manifold driver's side & a single wire one under the exhaust crossover pipe,also driver's side. You want to change the single wire one. Yes,it's tough. If it's still overheating quick, then it's a head gasket.

sounds like you could have some junk in your coolant system. I would try a complete flush maybe a couple of times with just water pumping through. you can get rust in there and even with a new thermostat as soon as a chunk of rust gets back to the thermostat ot can stick closed again.

reffer to owners manual