the engine runs great but the oil & coolant are mixing & pouring into the reserve bottle but not in the engine.
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1999 Ford E-250 Question: coolant & motor oil mixing in radiator
Answer #1ZeeTech February 12, 2011, 10:00Master
Looks like you have a bad oil cooler. Replace the cooler, flush the entire cooling system - you might need to do it more than once - replace the missing oil and that should be it.
Answer #2patrick mannion from Greg Solow's Engine Room, February 12, 2011, 10:02Master
I just looked at the workshop manual on the 4.6 and 5.4L engine both have an engine oil cooler on the side of the engine (at oil filter) with coolant hoses attached to it. Perhaps the oil cooler is leaking and allowing the transfer of oil into the cooling system. This problem is only going to get worse and needs to be fixed immediately. The cooling system will have to be thoroughly flushed out as oil will damage rubber coolant hoses.
i agree w/ other responses, failed oil cooler. easy enough to replace.