What did you expect ???? The inline on not inline thermostat does not change the operation temperature of the engine coolant. A thermostat dictates when the flow changes from bypass to radiator.
And does no other function. A thermostat does not make an engine run cooler or hotter. After it opens the flow to the radiator and closes the bypass, the engine coolant temperature obeys to many factors none being the thermostat. Clues: air flow, rpm, ambient temperature, climbing...

 

A thermostat does not make an engine run cooler or hotter


i don’t agree with that statement

 

With the black/dark grey soft spring Land Rover thermostat I see

185F moving
194F idle

On the highway with a load it will climb a bit but then usually come back down.

'03 D2 with normal coolant

 

Without a thermostat the engine runs much cooler. The bypass design constricts flow, and I believe an inline set up would allow the coolant to flow more freely and cool more effectively.

I could be wrong, but am fixin’ on finding out.

 

Without a thermostat the engine runs cooler a longer time until engine stabilizes its operating temperature, then the heating factors take over and the thermostat or no-thermostat-present does exactly nothing as it is in open flow state towards the radiator.
The thermostat exists to manage very cold ambient temperatures to allow the engine to reach efficient warmer combustion operating temperatures and closed circuit operation.
A thermostat is a very good thing to have in polar climates. Nearly useless in tropics.

To run without a thermostat, the bypass path must be eliminated, plugged, condemned to coolant flow and will not harm engine operation unless it is winter in Alaska.

Engine block out-------> in-line thermostat or not------->radiator------->coolant pump suction. And no other flow paths.

 

So more volume of coolant being sent through and circulated through the radiator and block wouldn’t cool the engine more efficiently? I would think that the increase in heat exchanges would create a lower temperature.

 

My understanding is that the inline mod is for the convinience of being able to use a commonly available GM thermostat, with simpler hose routing.
And, that an available 170 degree thermostat can be used in non SAI trucks. Using a 170 with SAI will cause dash lights.

 

I was always under the impression that it was about temps, but I could be wrong.

 

We are talking about coolant temperature the thermostat directly effects your coolant temp

 

That is exactly correct. The more coolant mass flowing trough the radiator per second, the more heat is dissipated. The lower temperature is not created but achieved by releasing heat; by the coolant heat exchange.
But the working engine coolant temperature obeys to other factors. An engine with or without thermostat cannot get cooler than to a certain limit. That limit comes from ambient temperature, rpm, air flow, coolant mass flow, climb rate, tow load, lead feet, mixture ratio...
There isn't a thermostat that can make the engine run cooler for a while since start-up than having no thermostat at all.