What ever happened when you felt the two hose when they were heating up? Did you sense blockage? You rad may have blockage>

What about running without a thermostate as previously asked? If you overheat w/o a thermostat, you gotta have a blocked rad (if you're not losing water volume).

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'89 420 SEL
'90 300 SEL
'68 Olds 88 Convertible
'84 300 SD (sold it)