I just removed and replaced my 12 year old radiator with 200k miles (1991 W126 350SD). I put in a brand new behr and filled the system with a mix 50/50.

The car is now running hotter than before. It doesn't overheat, but it likes to go to the 100C mark, where it do that before. And, it doesn't cool down as quick as it did with the old radiator. Then it will start behaving as it did with temps running 80-90C.

The system has been refilled and tests for approx -34F below. At one time, my mechanic lighted up the antifreeze a little to approx -20F below because he said it cools these beasts better.

Should I lighten the water/coolant mix up? Is there something I was supposed to bleed that I didn't?

Please help...

Thanks,
Richard