Changed water pump (Airtex Brass Impeller, on sale @ AB) , fan & clutch assembly(early D2, Torqflo 922302), thermostat (motored 180*), and coolant reservoir cap(original @ AB). Flushed and bled system as per Rave. Idle: 199*, 205* High temp. Running:199*. The reason I ask is because when I changed my original stat to Motorad 180 about a year and half ago, with original equipment I saw a 195* Idle that stayed constant for the 20 mins I tested it. This was before new radiator about 9 months ago, so I was hoping same or better results. Another possible factor is this time I went with premixed Peak, whereas before I bought concentrate and carefully mixed with distilled water. The reason I overhauled the system is because I was getting pressurization at the reservoir bottle, and decided to try and see if this would resolve it before I bit the bullet to do Head Gasket job. Your comments/opinions greatly appreciated!

 

I have used the motor rad in the past and your temps are in the range for on of them. I recently changed to a GENUINE GREY 180 from Lucky 8 and my temps have gone down to 188-194.

The motorad is better than the original one but not as good as the genuine grey 180

 

I don't think it is coolant mix related. A higher % mix of coolant will transfer less heat than a lower % mix of coolant (the specific heat of antifreeze is less than that of water). If you flushed your system, you most likely had some water remaining in the system. When you added the 50/50 premix you diuted the coolant % lower than 50. This mix would transfer more heat than the 50/50 mix. In addition it would be less viscous than a 50/50 mix resulting in more flow thru the system.

I would try a different thermostat. I have a motored 180 and run at 194. Others have posted that they are running higher than 194 with a motorad 180. I am going to go with a Genuine LR 180 next time I replace it to see if I can down below 190.

 

Testing today in San Antonio's 102* weather resulted in a high idle of 220, turned on heater to full blast to get home. Placed an order for original 180* stat at BP Utah, will remain parked until then, rebleeding to see if any air pockets are discovered. If this does not resolve it, an inline thermostat mod will be next, followed by selling her, even though she has been a great car, I cannot risk overheating her knowing about HG issues, and having recently moved into a newly built purchased home.