I actually drilled out my old thermostat yesterday. I'm planning on installing later this evening or tomorrow. I've bought 2 different thermostats. One was oem (the one currently installed) and the other was from lucky8. I tested the lucky 8 one and it opened at 180° so that wasn't the original reason for the overheating.
thanks for the help. I'll let you know what happens.

 

My personal bet is head gasket very hard hoses are generally over pressure, BUT try this as well run with your expansion tank cap completely loose as bad cap can cause over pressure.

 

agree...since OP provided more history of hard and hot hoses....sausage links? waterfall sound? head gaskets even been done?

 

This is incorrect. 100% your issue is the thermostat. Boiling it tells you nothing. Drilling it out does nothing. The factory thermostat design has a bypass valve in it. When the thermostat opens the bypass valve is supposed to close, they don't. It is literally impossible for a D2 to overheat on level ground if it is full of coolant and the coolant is going through the radiator. Even with a bad head gasket. The only possible reason for overheating is a plugged radiator or bad thermostat. You thermostat bypass valve is not closing and all the coolant is bypassing the radiator.

If you want to test it, get rid of the thermostat. Connect the top radiator hose directly to the manifold outlet pipe, put a hose repair kit splice in the bottom hoses were the factory thermostat goes, the kit is $5 at Autozone. It's plastic, so not the best long term but will do for a test.

 

Ok, I checked the serpentine belt and it's correct. Installed a new aux fan and that is working now so that's good but obviously had no effect on the overheating. I tested the original 180° thermostat in a pot of boiling water and it opens. I drilled out the old 'original' thermostat but haven't installed it yet.

I took the rover for a spin to see if aux fan was working and after checked the hoses....I noticed that all were too hot to touch except for the lower radiator hose. It was actually cool to the touch. Weird. Does that point to a thermostat that isn't opening? What are your thoughts?

 

Ok, I checked the serpentine belt and it's correct. Installed a new aux fan and that is working now so that's good but obviously had no effect on the overheating. I tested the original 180° thermostat in a pot of boiling water and it opens. I drilled out the old 'original' thermostat but haven't installed it yet.

I took the rover for a spin to see if aux fan was working and after checked the hoses....I noticed that all were too hot to touch except for the lower radiator hose. It was actually cool to the touch. Weird. Does that point to a thermostat that isn't opening? What are your thoughts?

 

The hoses do look like sausage links. I don't hear waterfall sounds. The head gasket has not been done to my knowledge.

 

Cool to the touch lower radiator hose means that coolant is not going through the radiator, just like I said. Two possible causes:

1. Plugged radiator (very rare).

2. Bad thermostat (very common) where the coolant is bypassing the radiator.

 

My radiator is brand new so I'll replace the thermostat again and see if that fixes it.

 

Instead of wasting money on oem thermostat designs just do an inline mod (sticky at the top of the forum). However, if you are insistent on the OEM design I have three brand new I am happy to send you for free if you pay shipping. I am never going to use them (because they never work reliably and cause things like blown hg, but whatever).