OK - I forgot your earlier comments, sorry about that - makes more sense now. The coolant shouldn't boil as long as your pressure cap is working properly, and is rated at least 1.2 bar (preferably 1.4 bar, which is the newest revision), AND you have a 50/50 mix.

BTW - bad gauge senders usually read low, at least in my experience that's the usual failure mode. Let's hope yours isn't reading low right now...!

Best way to clean the fins is *remove* the radiator (yeah, I know it's a real nuisance), clean the radiator while out of the car, and then you have full access to the back side of the condenser to blast compressed air AND water (using both seem to work best, rather than just one or the other) and get the condenser airflow back to normal.