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2006 Ford F-350 4D 4WD Lariat LB
22 Posts
Discussion Starter · #1 ·
I have a Ford F-250 6.0 and I have a Sinister bypass coolant filter and a new Stant degas cap. Coolant flush with Motorcraft Gold three weeks ago and full synthetic oil change two weeks before that, and I cleaned out the EGR valve with the oil change (2x a year for EGR valve). Truck has been running great with no issues - but about a week ago I noticed that the engine gives out a high rev sound like the fan is working overtime. It seems to slow the automatic shift and rarely spikes over 2k RPM. It dies down when the transmission shifts into higher gear. When at cruise speed (about 70 mph highway) it is barely discernible, but audible. At idle the engine stays about 700 RPM. No black smoke, just a slow to shift and high fan rev.

Any ideas what might be causing this? My friend says it is the air filter assembly, which looks ok (not too dirty). But he runs 50/50 veggie oil/petro diesel in a 6.0 and after replacing his injectors once already he still hasn't learned his lesson. I'd appreciate any suggestions on this.

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