When one removes the cap the o-ring fits snug against the inner wall. Between that wall and the outer wall there is a space and a hole/tiny drain. That space always gets wet (after driving), even after I dry it carefully then start the engine.

 

I did an oil change yesterday and while the underpanel was off got the rear wheel liner off and replaced the reservoir. The reservoir comes complete with cap and level sensor at the bottom. (Not sure if the parts guy didn't know but now I have an extra cap). The new cap feels slightly loose so I'm not sure if I stopped the leak. Temp still goes up to 201 F but someone shared should be 197 F if no leak...

 

My 4S runs at 200F in comfort mode once warmed up. If it is in Sport or Sport+ the water temp will drop and run cooler than that..

If you are reading 201F---- I would not consider that too hot. Visibly losing coolant is a different issue however.

Regards,

 

Thanks that's really helpful/comforting to know. I did notice the coolant temp drops in sport mode, too distracted by the engine revving in sport plus to notice what the temp is.

 

another data point: my coolant temp sits at 201 steady-state during long idling sessions

 

Thank you for sharing that. It does not allow me to rep your post saying I should spread it around... My initial guess it that the reservoir replacement did the trick. I ordered rubber stoppers (from WidgetCo) in all sorts of sizes and instead of draining the coolant first, I just removed the lower hose and plugged both the hose and old reservoir, (with a bucket underneath to catch what bled out). I then filled about a gallon and a half of coolant to get it to the mark. Within a couple of days I opened the cap to top it off. It no longer looks wet in the area with the drain, so hopefully no more leak...