overheating after rebuild

'89 s15 jimmy 143,000 miles. Let it sit in driveway for about 15 minutes running after first crank and it started heating up (top hose was hot as he@*). Turned it off, next day installed thermostat, figured it wasn't opening. Cranked it, let it run in driveway for about 15-20 minutes or so and temp was fine. Decided to go do a test drive. About 1/2 mile down road temp started going up again. Pulled over and turned it off and sat for about 20 - 30 minutes to let it cool off. After that cranked it and temp dropped to normal range and was able to get home. Let it run in driveway for about 15 - 20 minutes when I got home and it was fine. Next day cranked it and let it run for about 15 minutes and temp started going up again, hose hot as heck again. Tried burping system cause figured maybe an air bubble was trapped in water pump. Never got any bubbles coming out of radiator. Cranked it and after 15 minutes or so temp goes up again. I've done a few rebuilds on other engines and never had any problem like this. Any ideas?

What was the temp of the lower hose?

What was the temp of the lower hose?

Sorry just realized I put wrong info, the bottom house was hot, top was not hot.

Use a garden hose with a little water pressure to force air pockets out while the engine is idle and the HVAC on high heat max.

Use a garden hose with a little water pressure to force air pockets out while the engine is idle and the HVAC on high heat max.

Didn't help. I replaced water pump, thermostat and radiator (found a tiny oil at top). I let it warm up for 15 minutes and it starts overheating so I shut it off. Let it cool off for about 10-15 minutes, crank it then it stays at a normal temp. I am at a loss.

Is it actually overheating or do you think you have a bad gauge or sending unit?

Is it actually overheating or do you think you have a bad gauge or sending unit?

It's actually overheating.

I could start with taking some reference pics.http://www.derrckmde.com/12.jpg

Reference pics of what?

Are you sure T-sat is installed correctly?
Do you have electric fans? if so, are they coming on?

Are you sure T-sat is installed correctly?
Do you have electric fans? if so, are they coming on?

Yes thermo is installed correctly. And the fan is coming on. Seems like if it was a sensor or something like that then it would always overheat. After I warm it up, turn it off for a bit to cool and then crank it up and run it's fine and at normal temp. The only thing I can think of is an air bubble under the thermo and after a cycle it passes and is fine.

Yes thermo is installed correctly. And the fan is coming on. Seems like if it was a sensor or something like that then it would always overheat. After I warm it up, turn it off for a bit to cool and then crank it up and run it's fine and at normal temp. The only thing I can think of is an air bubble under the thermo and after a cycle it passes and is fine.

Someone suggested running it without the thermo in (light driving) a few times and see if that will help get out any air that may be in there. I have been doing that for a few days, just to and from work. It's fine right now. Temp doesn't go up, stays in normal range. I'm going to put the thermo in at the end of the week and see what happens. If it still overheats then I have no freakin idea what it is. I've tested the thermo in some boiling water and it opens so it's good.