My b17 does that as well, cant leave her running for too long or the temp goes up to 210 and thats when my fan finally kicks on. Already put in a Spoon Sports thermostat which did no good. Figured my next step would be a better radiator (still stock). I had a ton of air in the system on my 240 and just resolved her heating issue by parking her on an incline to get it all out.