I have a 2000 blazer 4.3land I just changed the engine.vehicle runs good but I am losing fluid
I can find no leaks and no white smoke coming from the exhaust
What can it be? I have no thermostat in it and it shows that it's heating up
Thanks for your help

 

Check the oil for presence of coolant in the oil. (chocolate smudge)

You cannot run the Blazer without thermostat (actually any vehicle).
The internal balance for the water flows is not correct that way and it may not route the water properly through the radiator.

 

Checked oil and did not find any water in it. I refilled my radiator with water and drove it about 9 miles and it was showing the temperature of around 200*. Could it be the LIM gaskets maybe head gaskets. still can't find anything leaking.