986 Running hot (Found solution)
 

Posting this for posterity:

Symptom: 1999 986 running with temps regularly above the "180" on the temp gauge.

Mods: after market headers, cat delete, RoW programming, after market exhaust, low temp thermostat.

Solution: moved from Peak pink coolant to Prestone for all vehicles.

Result: stable temps from the third mark to the right edge of the "180"

Notes: the Peak was purchased mid 2020, water wetter was added later on with no change in temps. This is my second 986, previous ran on porsche coolant then eventually prestone after changing the pump, both gave a low and stable temp.

For a long time I thought the temp was just the result of having a less restrictive exhaust.

If you're having problems with your temps then try changing to a different coolant.

Sorry, but that makes no sense. If you run these cars on pure water, they run fine and at the appropriate temperatures, customers running the entirely wrong types of coolant do not have over heating issues; so why would this particular coolant cause this?

No idea-- when I changed it, I didnt flush the peak coolant, just drained and refilled; all the seals, caps, and clamps are the same.

The peak has Potassium 2-ethylhexanoate and Sodium 2-ethylhexanoate, in addition to the glycols. The prestone only lists glycols and bitterant.

None of which would alter the thermal transfer properties of the coolant mix. Something else was wrong, like a stuck thermostat or a trapped air pocket. It was not the coolant............