Have you actually used an infrared thermometer and checked the engine's temps in various places (top of radiator...water pump housing....upper hose....intake area...sensor area) to see if its actually running at those temps?

The engine fan should be ROARING above about 85C.......the one on my 420 fully engages over about 84-85C and moves a TON of air, my front aux fan also comes on low around 85C With the A/C on.....

I just did the intake job on my 420 a few weeks ago and did not burp anything, I filled the coolant just by filling the expansion tank and running the engine...0 issues, runs at 82-85C, even sitting idling with A/C on a hot day it never even hits 90C. I am running about a 45% mb coolant to 55% water mix in mine right now.

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