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Join Date: Apr 2010
Location: Clinton, MS
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That temperature difference is fine - discretely. There is insufficient evidence for the evolving 10-degree indicator...it is a 15-degree indicator (based on the preponderance of warranty claims post-failure where the 25-degree delta was a false panacea). Perhaps watching the delta climb from a 6 to 8-degree difference to a 10 to 12-degree difference is applicable to indication of restriction in the oil cooler but without that degree of specificity then to characterize any delta below 15 is specious.
I am guessing that the OP is running unloaded as the ECT is below the opening threshold of 192-degrees; either that or the thermostat has failed open. Also not knowing your gearing means that it is speculative to determine whether the OP is running in overdrive or a lower gear by travelling at 80mph. The conditions for oil cooler efficiency begin with an engine at operating temperature (not cold start conditions) and highway speeds (55-65mph...not 80mph). It is conceivable that this engine - operating hard against wind resistance - is at the upper end of its powerband running in 4th gear. Even if it is in OD more fuel equals more heat on the oil. That little oil cooler is a marvel but it is a little oil cooler.
My truck has 4.88 gears. I don't think F-350's have better than 4.10s and typically are 3.73s so this is all academic at this point.
...but the temp spread (under the less-than-compliant conditions identified) is fine...
Better to get an assessment under the correct conditions.
Jonathan D. Howell
Lieutenant Colonel, U.S. Army
2005 EarthRoamer XV-LT (Ford F550)
"Americans Travelling America"