Understandable, but for another data point, I have driven stock, in warm weather, much further than 5KM at rpm between 7000 and redline and have never had the coolant light come on. I did change the coolant early on, with fresh 50/50 mix, and took care to follow the workshop manual (bleeding).

It's possible that your problem was fixed by effectively lowering the water pump rpm. It's also possible that the act of draining and refilling the system took care of it. I'm sure neither one of us wants to test all the parameters, but for someone having the problem it's cheaper to try a flush/fill/bleed first.

 

Just for the record, I didn't do a flush/fill/bleed. I just put on the pulley. I could think of half a dozen reasons why this could be, but I haven't had any overheating problems or anything yet. Maybe the pulley is just masking a bigger problem.....

 

I've had that problem and here's what I've done twice that stopped it. It happens after I drain some antifreeze installing something or other. Air gets trapped during the reassembly. Best solution is to find some ramps or a small hill you can stop on or even jack up the front of the car if you a floor jack.

Best if the car is cold when you start. Warm the car for 5 or 10 minutes until water flows to the radiator. Then with a rag, gloves and good face protection CAREFULLY loosen but don't remove the radiator cap. Let the pressure of gradually if possible and you'll likely find a lots of bubbles coming out of the overflow feed tube. It shouldn't blow out if you haven't let it idle too long. When it stops bubbling, tighten the cap.

Don't do it if the car has been driven, just warm it up from cold. You could easily scald yourself that way.