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Coolant bleed after replacing rear coolant pipe adapter?

enobiko

Go Kart Newbie
Location
NE Ohio
Car(s)
2017 SE 6 MT
I replaced the rear coolant pipe adapter above the turbo, because the plastic one was leaking. Everything went well, I topped off the coolant reservoir, then ran it for a while, then re-checked and refilled the coolant reservoir. Should be good, right? A couple of hundred miles later...
I was gassing up and left the car running (!) because my wife was on speakerphone. The cooling fan kicked in on high after a while, which sounded odd... I've done autocross 5 times over the summer and left the car running after each run (in order to get coolant circulating to the hot spots, like the turbo) and never had an issue. Trouble is... when I went to look at the temp gauge, it *may or may not have been* almost into the red zone. Or... did I mistakenly look at the gas gauge instead??? Maybe so, because I pulled away from the pump and turned the car off, looked in the engine bay... no leak at the new pipe adapter, no loss of coolant in the reservoir... and when I turned the car back on, the coolant temp was exactly where it should be, at the 12 o'clock position. I've paid attention (before and after) and the coolant temp has never gone above the 12 o'clock position or done anything weird.
Is there some kind of air bubble in my system that may have caused a hot spot? If so, I didn't see anything that indicated how to bleed the system. (Thinking back to my 1971 Fiat 124 Spider with an external thermostat, a nightmare to bleed.)
On the other hand... this was one instance, and I have been questioning if I saw what I thought I saw. The car was not run hard at all prior to pulling into the gas station, but I did idle for a bit before I was able to pull up to the pump. I don't mind the cooling fan kicking in, but if I have an air bubble trapped, I would want to address that. I think that is unlikely, actually, given there are no other indications, but this is stuck in the back of my mind...
 

2018gti

Drag Racing Champion
Location
Boston, MA, USA
Car(s)
Golf GTI Autobahn MT
I think given that you don't know for 100% that the needle was around the red zone, I would just wait and see if it happens again. was the fan going faster than just the usual AC is on, fan starts up occasionally kind of speed? maybe you could try running the heater on high to get any potential bubbles out of there. when I replaced the adapter on mine (twice) I really didn't do anything special, just refilled the reservoir (which had emptied) and ran with the cap off for some time, possibly with the heater on.
 
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