The bar on my Mac got hot at first too. There were two problems:
1. The chain was too tight.
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I'd go for the chain too tight.
A properly tightened chain does not "snap" back to the bar. At it's tightest, it should still have about 1/8" hang below the bar. The only reason to tighten the chain is to keep it on the bar.
When the chain gets hotter, you need to let it have more hang, so that it won't be too tight when it cools.
When you run the chain to tight, you put huge forces on every rivet with every bend around the 2 sprockets. Despite all the oil in the world, that back & forth bending will create a lot of heat. Furthermore, it wears out chains very quickly!
Do you find yourself tightening the chain all the time? If you are, it's because you are overtightening; the chain "stretches" (wears out each rivet hole) until it has about the right tension...then you tighten it up again.
If you are running a big bar, you need to learn how to run it loose without throwing the chain. My 50" bar will hang 1"- 2" below the bar when it gets hot. If you tighten it up very much, the chain quickly stretches back to that point. Leave it loose and you can go that way for hours without tightening it more. Of course, it's been a long time since I had "hours" of work for that big bar. Usually, it's 15 minutes, and then everything is cut up.