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I can sure agree about that lack of economy, barely drove the thing and I'm already 1/3 a tank down on gas.
In my area they sell ethanol-free 87 octane,,
You think 5W-50 would work well for my engine?
In short - yes. There are two main areas of concern when lubricating any engine, but particularly older ones: the first is getting oil to the upper areas of the engine as soon as possible after firing it because tests show that a great deal of engine wear occurs immediately upon after startup when the engine is cold, oil pressure is low, tolerances are tight and oil has drained from parts leaving metal on metal contact until adequate oil pressure can be achieved. Older engines need this protection more because they lack the roller tipped valve train of modern cars and are more susceptible to wear in those areas. Some tests suggest that every cold start with inadequate lubrication is equivalent to driving several hundred miles. So, we want oil that is as thin as possible when cold in order to get oil pressure up as fast as possible. The second area of concern occurs at higher RPM and sustained highway speeds (older cars rarely have more than three or four speed transmissions so engine RPM tends to be higher during highway driving). Again, tests have shown that 50 weight oil provides the best lubrication under those conditions (some research states that 50 weight is the only oil that provides adequate protection at higher RPM). Most racing oil is straight 50 weight but that won't work for daily drivers because that is far too thick for cold starts (it works for racers because they commonly pressurize the oiling system before firing the engine). So, for daily driving - especially older cars - ideally, we want oil which is thin when its cold and thick when its hot. Tough to do with crude based oil which breaks down if the additives used to achieve multi-viscosity are stretched too far. You will never see 5W-50 crude based oil - only synthetic can achieve that desired multi viscosity. In simple terms, the first number of an oil's "weight" indicates its viscosity (i. e. its thickness or ability to flow) when cold, and the second number indicates its viscosity when the oil is hot. The thinnest oil when cold and thickest when hot is 5W-50 and that can only be found in full synthetic oils. There are many other reasons why synthetic is better: it keeps contaminants in suspension better and drains them out with the oil change (rather than allowing dirt to percolate out of the oil as it cools, resulting in sludge); synthetic also provides a harder oil film between parts and will tolerate far higher operating temperatures before breaking down. Synthetic oil also lasts much longer between oil changes and although I personally follow the same oil change regimen as I would with crude based oil, you will note that Mercedes, BMW, Audi, etc., etc., etc. come from the factory with synthetic oil and their recommended oil change routine is 12,000 miles (20,000 kms) or once per year. I change oil once a year in all my classic cars, usually in fall, before I store them. Synthetic oil is not usually recommended for use in newly rebuilt engines until such engines have been driven/broken in for 10,000-15,000 miles because synthetic oil provides such an effective barrier to wear between metal parts that it will not allow parts in new engines to wear in or 'mate' properly, which may cause the engine to smoke. That alone should be a convincing argument for the superior protection offered by synthetics. Laboratory built oils cost more but it's still cheap insurance for an engine compared with cost of rebuilds. BTW, most experts suggest than 10 lbs of oil pressure for every 1,000 RPM is adequate for street cars so, forget high pressure oil pumps (not to be confused with high volume oil pumps which are desirable).
BTW, synthetic oils also seem to have higher levels of ZDDP than crude based oils. ZDDP is very necessary for older, flat tappet equipped engines but those additives have been greatly reduced in most modern oils (to reduce pollution). I believe that Castrol Syntec has the highest levels of ZDDP and that's what I use but I always add a container of ZDDP at every oil change as well..
The Owners Manual for my '79 states: " . . . minimum octane rating as designated by any of the following numbers: RON: 91; Average of Research Octane Number and Motor Octane Number (Antiknock Index): 87
