Here is a consideration:
The following piston is out of my sons KX 85, on this piston there are:
16 2 hour hare scrambles for 32 race hours
3 motocross weekends for another 12.5 race hours
12 weekends of riding at 6 hours per weekend (very conservatively) 72 hours
5 practise days at the local track at 4 hours per day for 20 hours
Total 44.5 race hours and 92 hard riding hours, 116.5 hours total.
Factory recommended piston replacement interval is 20 hours.
I pull the pipe, spark plug, and drop a camera inside the cylinder after every race while servicing preventatively.
If you know anything about a 85CC 2 stoke motocross bike, that is pretty darn good, they can be hard on top ends. The engine is substantially smaller and, much higher performing than the mentioned VW engine. It is jetted pretty much perfectly, hence the lack of any carbon on the piston, so cylinder temp is not on the edge, but not far from it. We run Evans coolant for the stability and to prevent overheating which will pretty much wipe out a 2 stroke piston and cylinder, we also run Amsoil Dominator race oil, we run this stuff in everything.
So here is a consideration, especially for those hot summer days, you blow a fan belt off and don't notice it in time, especially in an older vehicle without warning lights or shut downs, your engine hits 250 or 260 before you realize it, but you don't blow all your coolant out, you are able to let your engine cool down and continue on for short bursts if nothing else, and your engine is really no worse for wear. In my case i was able to drive my F-650 with a C7 Cat 60 KM's down the highway to the next town where I could repair my failed fan clutch, the temp gauge sat at 250 with the warning light on steady, but that's where it sat, no tow bill, no replacing coolant that boiled over. And I was on a seriously busy highway with no room to be messing with a broken down truck. Who would disagree that it's a pretty good safety advantage?
So if you are doing a rebuild, a restoration, a cooling system upgrade why not throw it in? Rely on your rig to the point that an overheating situation could endanger your life? I'd say use it. If your trying to fix an overheating problem, fix the source of the problem, don't band aid it.
KX85 piston:
My F-650 and the derelict fan hub that got a couple of 3/8 bolts drilled through it to lock it up after it failed:
http://www.expeditionportal.com/forum/images/attach/jpg.gif
http://www.expeditionportal.com/forum/images/attach/jpg.gif