<VV> hot motor oil

[Ken Clark]

Since the motor oil topic came up again I have a question concerning oil when it gets hot(engine running temp Corvair).  A few years back I made a 1000 mi. round trip to Helen Ga show.  The engine did not use excessive oil, maybe a qt. in 400 mi.  I was told Mobil 1 was the way to go, so changed to MObil 1 before the trip.  Used about 8 qts round trip.  A Mobil(expert) tells me that the oil is thin as water and runs right through the engine.  My thought is that any oil is thin at engine temp.  Changed back to 10W40 Quaker ST. and did not have usage problem.  Any thoughts on this situation?
By the way, everyone(almost) used STP back in the 60's and did you ever take an engine apart that had been using it?  I've taken pans off that were covered with 1/2 inch of sludge.  I 'm told that was from STP and other additives.  Not sure, but know what I've seen.
Ken C