HOW big of a temperature delta between ECT and EOT is the "danger zone"?

[ColdFoundry]

I'm monitoring my 2006 6.0L with an Edge Insight. Cruising at 65mph, my Coolant Temp (ECT) is 192°F, but my Oil Temp (EOT) is hitting 210°F. That’s an 18-degree delta. HOW close am I to a catastrophic failure? I’ve heard 15 degrees is the limit before the oil cooler is considered "clogged." Should I try a chemical flush (like VC-9) first, or is it a waste of time once the delta stays this high?

 

[WrenchWhisperer]

The Ford spec is a 15-degree delta after the truck is fully up to operating temperature and cruising at 65mph on flat ground. At 18 degrees, you have officially entered the 'danger zone.' What's happening is the tiny cooling passages in your oil cooler are clogged with 'sand' (casting sand from the block) or silicate sludge. This starves your EGR cooler of coolant, which is usually the next thing to blow. You aren't at 'catastrophic failure' yet, but you are driving a truck that is slowly suffocating its own cooling system. I wouldn't tow a heavy trailer until that oil cooler is replaced.