Also look for coolant residue from loose hoses or pin-hole leaks, and fan motor bearings.
I was having heating problems years ago, and found two issues:
1) The hose clamps were a bit loose due to the hose rubber taking a set from age.
2) I had shifted over to Engine-Ice and noticed purple coolant residue on the left cowl.
After investigating further, I found the left upper radiator tank had a hole in it the prior owner had patched with JB-Weld, which does't work with radiators, due to the expansion and contraction of the metal.
After having the hole welded and pressure tested, I ceased having cooling issues.
On a hot summer day at idle in traffic, it would not exceed 218, which the fans quickly dropped down to 208. Once moving, the temp dropped even lower.
And in the spring, with temps in the 80s, I saw temps below 180 degrees while on the move.
3) For either SP1 or SP2, check condition of the fan motor(s).
With the engine off and cool, try to spin fan(s) by hand. They should easily and freely spin.
When I was refurbishing my SP2 (due to prior owner), I noticed left fan motor bearing was squeaking when rotated by hand and would immediately stop rotating, plus indication of fan blades rubbing against the radiator fins.
I corrected the fan to radiator clearance issue, and replaced both fan motors.