On the way home, the oil temp once again rose to a very high level (over 250 degrees). After I got home I checked the oil level, with the new dipstick, and wound up taking out almost a pint of oil to get the oil level down to what it is supposed to be.

At this point I am wondering if the thermostat is not opening completely in the oil cooler?

Could it be the Amzoil? Although I was told that using Amzoil should lower the oil temps.

Most people run synthetic. I run synthetic. I don't do this because I hope the engine lasts 200,000 miles. I won't own the bike anywhere close to that long. I use synthetic because the engine runs cooler, and I get a little bit better mileage. There are other benefits like greater thermal protection and better cold flow properties that provide oil flow quicker on cold start up, but again I won't be the one who owns the bike during the last 20% of its life. Having said all of that, it is impossible for me to provide any factual data about engine wear or longevity on conventional vs synthetic oil. But the facts speak for themselves - we don't have heat or lubrication related failures in twin cams. This was true for the three years the twin cam existed before Harley started selling synthetic oil, and it's true today. Things may be a bit different in the desert southwest. I suspect they have some occasional heat related failures, but out here despite our gridlock traffic and 95 degree summers we still do not have heat or lubrication related engine failures. We don't see burned valves, melted pistons, rings that have lost their tension, broken rods, wasted flywheel bearings, or anything else like that. The Twin Cam engine failures we see are very rare, with us rebuilding or sending out for reman only a handful per year. We build lots of engines for performance, but for actual failure purposes I'll bet we don't completely rebuild or reman 15 engines per year across three dealerships and thousands of bikes serviced every year. Of those very rare failures, the most common causes are cam bearing related. We're seeing about 3 - 5 engines per year that spin an inner cam (needle) bearing, thus destroying the case. We see a couple to a few that might ingest some pieces of a tensioner shoe. A couple of big end bearing failures per year, likely because some kind of foreign material went through the bearing. Perhaps a couple of engines with shifted flywheels per year. That's about it. That's pretty good for a dealer group that has a 35,000 customer database. Despite that very low failure rate, I cannot count the number of bikes we see every year that come in with less than a quart of oil left in them. Or sometimes, no oil at all. I've seen a bike come to us that had the oil changed and no oil was put back in, and the customer rode the bike a claimed 400 miles like that. I've seen bikes that idled in 95 degree heat for so long the engine finally shut down, only to cool off, fire right back up, and run fine. Engines that got so hot the exhaust heat shields blued. Engines whos owners claim the oil hasn't been changed in 50,000 miles (and it looked like they were telling the truth!) Despite all of this, the oil is never cooked into sludge and they keep on running. I've seen engines running for well over a thousand miles with the compensator nut backed off and the crank bouncing side to side (tightening the compensator is part of what controls end play in the bottom end). I don't think there is a Japanese, Italian, or German production motorcycle that does a better job of tolerating the abusive, neglectful behavior of some of the owners. The Twin Cam is an incredibly well engineered, understressed engine that had some teething problems in the early years but has turned out to be quite a gem. Are the late EVOs better than Twin Cams? I have a soft spot for EVOs. I like the sound and feel of riding a bike with that engine. The only big twin EVO I owned was a '98 Wide Glide I bought new. I did some performance stuff to it and had a great running bike that never lost a race. I still miss that bike. But I wouldn't even begin to say it had a better or more durable engine than the Twin Cam. It isn't even comparable.