I'm fairly sure I've narrowed this down to an ECU fault and rather than deal with that I'd rather just bypass it.

Which gets me to the question of at what temperature should the fan turn on with the slow speed, and when should it turn on the high speed?

I've seen some comments that the fan turns on after boiling, but I'm not sure how much. Though my last car, a Volvo 97' 850 T-5, cycled on at roughly 210-215 and took it down to 190 (idling) if I remember correctly (been a year or two now though).


My current car is a Volvo 99' S70 2.3L turbo.



I have tried searching but have so far failed miserably as I keep dredging up people with coolant problems who are replacing the parts, and not interested in when exactly it turns on. If someone can find a link I would love it if you can post it here .

 

I'm a fan of fixing thing "right", especially when dealing with something as critical as the coolant system but here you go.

I also have the 2.3L engine but in the 850. I run a ScanGauge and monitor coolant temp all the time while driving because I know that overheating an old car will likely be the death of it. You are pretty much right on. The fan turns on at about 192° and the high speed kicks in at about 210°. Not sure what you're going to do to "bypass" it but it sounds like a lot of work bypassing it and operating it after the bypass.