Oxalic acid has been considered a good flush for more than 50 years.

https://www.astm.org/stp25166s.html

I can tell you from experience that CLR works NOTHING like it is shown on TV. The dip & clean demonstration they depict is a complete farce.

I will also say this: I had a 78 Super Coupe back in the later 80's & the engine always ran hot - something was not right with the cooling system, also the coolant always was brown even after flushing the system & using new coolant. Radiator looked good internally, but I pulled it anyway & had a radiator shop boil it out & pressure test it, then reinstalled along with a new thermostat & water pump. SAME scenario - running hot & dirty looking coolant. Finally on a slow day, we pulled the engine due to a freeze plug that was leaking - it was one of the ones that you could not do with the engine sitting in the cradle. So the plan was to replace all the freeze plugs with new ones, clean & paint the motor & the exhaust manifolds, etc. - reinstall. Upon knocking out the large freeze plugs on both sides, we discovered SO MUCH sediment in the passages - like mud. We hosed it all out & a LOT of crap completely flushed out pretty quickly & easily til the water ran clear. Installed new freeze plugs, painted the motor & reinstalled. This completely took care of the issue. I'll tell you this, there is no way you can effectively flush a motor that contains sediment unless you pull the freeze plugs. This was the ticket.

I can tell you from experience that CLR works NOTHING like it is shown on TV. The dip & clean demonstration they depict is a complete farce.

I will also say this: I had a 78 Super Coupe back in the later 80's & the engine always ran hot - something was not right with the cooling system, also the coolant always was brown even after flushing the system & using new coolant. Radiator looked good internally, but I pulled it anyway & had a radiator shop boil it out & pressure test it, then reinstalled along with a new thermostat & water pump. SAME scenario - running hot & dirty looking coolant. Finally on a slow day, we pulled the engine due to a freeze plug that was leaking - it was one of the ones that you could not do with the engine sitting in the cradle. So the plan was to replace all the freeze plugs with new ones, clean & paint the motor & the exhaust manifolds, etc. - reinstall. Upon knocking out the large freeze plugs on both sides, we discovered SO MUCH sediment in the passages - like mud. We hosed it all out & a LOT of crap completely flushed out pretty quickly & easily til the water ran clear. Installed new freeze plugs, painted the motor & reinstalled. This completely took care of the issue. I'll tell you this, there is no way you can effectively flush a motor that contains sediment unless you pull the freeze plugs. This was the ticket.

Not sure why you think you have a problem.

185 is perfectly fine, in fact running a 160 thermostat in a street car is not ideal. It sure isn't what the factory specified.

Not sure why you think you have a problem.

185 is perfectly fine, in fact running a 160 thermostat in a street car is not ideal. It sure isn't what the factory specified.

The factory was worried about block and ring wear with that recommendation, most motors will make more power at 160F operating temps. than they will with the same tune up at 180F

Have you checked the exhaust for restrictions? That would cause an increase in coolant temperature, especially at highway speeds.

Drove it home again today.
Same results. going in this morning it runs right on the 160 temp of the thermostat. Ambient temps were mid 60s I think

coming home this afternoon with ambient temps right at 100 it gets to 160 fairly quick, little slower to 180 ish
But about 6 or 7 miles on freeway at 70 mph it runs up to a clik under 200. ,,,maybe 198-199 range.
Once off hiway it takes maybe 2 or 3 miles and cools back down to upper 180s range

Running warm at highway speeds is usually a water flow issue.

Poor flowing radiator, wrong pump pulley or pump, thermostat not fully opening, etc.

I've used vinegar to flush the cooling system, remove all water/coolant, block drains too, fill with vinegar, warm up, let set overnight, flush and refill with proper coolant mix.

One thing I didn't see specifically addressed, is your exhaust flapper opening as it should?

Is the radiator correct for the engine-car? Is coming ‘home’ more uphill? Or change of altitude? At speed the fan and shroud mean nothing, you have airflow. Stopped up, fins closed off or not enough surface area the radiator isn’t getting rid of the heat, that simple. A Hi VAC friend told me once that a temp of 210 can drop 30 degrees to 180 faster then 180 to 150 degrees, outside temp differential being the same. So when you say up at 60 and back at 100 that’s a 40 degree change. It’s harder to cool at 100, your water can’t get any cooler than 100, (outside temp) give or take a few degrees. So my guess you have radiator problems, not fan, not shroud

Running warm at highway speeds is usually a water flow issue.

Poor flowing radiator, wrong pump pulley or pump, thermostat not fully opening, etc.

I've used vinegar to flush the cooling system, remove all water/coolant, block drains too, fill with vinegar, warm up, let set overnight, flush and refill with proper coolant mix.

One thing I didn't see specifically addressed, is your exhaust flapper opening as it should?