I'll do a flush this weekend, as for the aux fan, I tried running it with a hot rad and it made little difference.

any way to lock or otherwise jam the fan clutch solid, I don't mind extra noise or parasitic drag. something temporary till I can eliminate this problem....which may do so in and of itself...

__________________
RIP: 80 300SD
RIP: 79 450SEL
2002 E430 4matic (212,000km)
2002 ML500 'sport'

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FACEBOOK: PANZER450

if the aux fan made little difference then it may not be the fan clutch. The aux fan pushes a large amount of CFM. As far as locking the clutch, you may be able to have someone weld a scrap clutch solid for you? I wouldn't try anything too drastic, a broken clutch & flying fan blade can spell disaster.

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Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k

I wired my aux fan to relay/switch, and with the fan on it does help a little, it keeps the temperature around 84-85 I did notice that under a load, say going up a hill, the temp rises but drops back down a bit when I ease off the throttle.
It's roughly 22*C outside right now, and it didn't get as hot as it did in the past. If I turn the aux fan off, the temperature climbs quickly to around 100. turn it on again and it has no effect.
Ok, so what's up?

In what I've seen with my cooling system, I'm more inclined to believe that it's my radiator that's faulty, boiled out. The fan clutch although suspect, still moves quite a bit of air, ruling an air flow deficiency. Thermostat opens when it should. Water pump works well, so that leaves the radiator...and this next thread...

__________________
RIP: 80 300SD
RIP: 79 450SEL
2002 E430 4matic (212,000km)
2002 ML500 'sport'

____________________________
FACEBOOK: PANZER450

The fact the e ngine is cooling down again when you let go the throttle means the radiator isn't blocked but your fan clutch is barely working . A LOT of air should flowing when the engine is at idle and hot. If it's simply a breeze and not making much noise ,then that is your answer.

The temp drops maybe 5* when I turn on the aux fan. I had the car in my shop earlier today, with the aux fan running, engine fan going and a shop fan blowing and it still was pushing 100*

__________________
RIP: 80 300SD
RIP: 79 450SEL
2002 E430 4matic (212,000km)
2002 ML500 'sport'

____________________________
FACEBOOK: PANZER450