195+- degrees. It has to run a little warmer than thermostat to reach a proper temp for emissions.This is higher than engine was originally designed for (180+-) and part of the problem. There is little wiggle room to run these 40 year old designed engines at modern engine tolerances (higher temp for cleaner burn).

 

According to RAVE the thermostat starts to open at 179F and is fully open by 204F. So 204F +/- a few degrees, but I'm with you I don't worry too much about a few degrees.

 

The only things that get "out of spec" are the same things that will cause overheating with an inline thermostat. Clogged passages, bad fan, air leak, inoperable thermostat, old coolant, etc.

And I'm not sure what point you are making on the heater core. Positive water pressure is coming from the upper Intake, the same passage that feeds the upper rad hose, and is being simultaneously pulled to the pump input. This loop prob had less flow than the rest of the system with the stock thermostat but it would be the primary circuit with an inline with closed thermo.

 

Might be a bit off topic. Im not really a mechanic but I can follow you guys but what reason why it need to run higher temp for cleaner burn? There are cars that run regular and I guess maintain proper emissions. Yah, I guess its the design. Was there anybody in 16 years found a better way to hack it better? Hack the engine? Do internal bypass or something? Increase the size of the small water hole in the engine block? Get a better water impeller. Add external oil pump etc. HAHAHA! Theres probably at least one genius in this forum. LOL! Must be driving a Range Rover? Hehe

 

Again you correct on the out of spec issues, except for one. The factory thermostat mixes the bypass coolant and radiator coolant to achieve an expected temperature compromise. When the out of spec things happen it streeses the system. Whether a clogged radiator, unchanged coolant, bad pressure cap, etc. the expected temperature and timing of reaching it fluctuates. The inline is how the engine was originally designed for. It does not mix the hot and colder coolant AFTER the radiator. It merely sends coolant to the radiator when it gets to a certain temp. If the system is out of spec it is not a problem until the thermostat is open all the time and the radiator cannot keep up.

As to the heater core, neither the factory thermostat nor an inline is in the core loop. The thermostat being at the exit of radiator is no different than being before the entrance to the radiator. Either location is irrelevant to the heater core loop. The factory bypass will merge coolant at the mouth of the water pump if thermostat is closed. The inline will shut off coolant to the radiator until opened. But while the inline is closed, the heater core loop STILL CIRCULATES independently of the radiator loop.

 

Theoretically, the hotter you can keep the cylinder and therefore the overall combustion energy, the more efficient and powerful the engine would be. But the materials available to us in mass production can't handle sustained heat and pressure like we would want for optimum efficiency.

if you could keep an engine heated to 500 degrees without the meterials fatiguing it would be more efficient than one that runs at 200. Especially if that heat is a byproduct of high compression.

 

The point being made is that while the inline is closed the heater core is pressurised more than when the thermo his open. It isnt a completely separate system. It shares flow with the res of the system and when you cut off the main flow passage, I.e the circuit made closed by the inline thermo, then you force the majority of coolant flow to the heater core. There is physically nowhere else for it to go other than the small bypass holes in the thermostat when the thermo is closed

 

Without measuring flow under these surcumstances I couldn't say whether the inline thermo, while closed, is enough obstruction to cause the heater core to overpresurise, but it's a valid concern in my eyes when considering the design of the system.

 

Around the early-mid 90s, the EPA started focusing heavily on startup emissions. Prior to this, the catalytic converter was the primary means of meeting the existing requirements. Unfortunately they only work when they're hot. The new standards required manufacturers to scramble and come up with methods of getting the catalysts to heat up as quickly as possible, or risk not being able to sell their car.

Most took the logical approach, and implemented improved engine management, while also moving the cats closer to the engine. Rover apparently decided to throw a bunch of complicated band aids on instead.

 

You are forgetting about the pressure cap. It protects the system from overpressurising. There's a reason it has a pressure rating that you don't go over when replacing a defective cap. They can fail to a lower rating and reduce the boiling point of the coolant, but they act as a failsafe above max rating and don't fail to a higher rating. The system is safeguarded unless you use a higher rated cap.