Not the thermostat....knew it.

Have you flushed it?

 

As someone mentioned already.... confirm the belt routing is correct.

 

It’s the sensor. Get one from AB, went through the same crap — check my build thread

 

The only thing that makes me think it’s NOT the sensor is that the lower thermostat hose is still ice cold after running for 10 min. Realistically it should have opened up by then and flowing warm coolant

 

I didn’t replace it. But I did put it on my other disco to confirm it seals and yes, it was working fine

 

It it should have opened ? Yes if it’s not your water pump it’s your thermostat if no air in system. What else could it be ??

 

To run without thermostat you must block the bypass hose. Inserting a golf ball in that hose worked great for me 50 years ago on my '68 BMW. Coolant flow must go only from engine block to radiator inlet, and radiator outlet to coolant pump suction.
I run an in-line thermostat on the Rover with no bypass path.

 

Yes, but your inline is after the coolant exits the block. If you put in in before the coolant enters the block, where the stat is now, it will stay closed due to the cooled coolant from the radiator. Correct?

The OP just did his head gaskets. It's possible some junk got lodged in the stat...but I'm betting, front up high on a steep incline would help.

 

Yes, but your inline is after the coolant exits the block. If you put in in before the coolant enters the block, where the stat is now, it will stay closed due to the cooled coolant from the radiator. Correct?

The OP just did his head gaskets. It's possible some junk got lodged in the stat...but I'm betting, front up high on a steep incline would help. Having air in the stat is also a possibility.

 

I was right