Overheating symptoms are the same in the aircooled beemer as in all other air-cooled engines.
Excessive valve wear (loosing valve-play quickly)
Then as temp rises:
- sluggish engine performance; jamming bearings...
- seized pistons/barrels and or crank
=> new engine...
It is never good to accept >130'C on the engine oil, but situations may force one to accept higher temps. As I wrote, my R80 have had >>180'C, and that did not seem to affect the engine much though - but valveplay dropped within 30-60km (!!!). Got tedious to adjust the valves every day...
I -strongly- recommend to make adjustments to handle periods of high engine temp; it is a bit of work and may cost a few quids, but in the long run it is woth it.
If you drive in areas with tempratures that get very high (>>35'C), your engine will really appreciate an oil-cooler or two. My experience is that the air-cooled engine prefers to have oil-coolers, preferably thermostat regulated. However, be ware, the beemer engine have an operational oil-pressure of 7 bars (+/- 1 bar); and a cold-strating pressure at summer that can hit 13-15 bars for a few seconds up to a minute. At winter, the cold-stareting pressure may hit >>22 bars!
So, Lockhart oilcoolers or any other cheap stuff will not do. You must use oilcoolers for hydraulic pressure, like www.setrab.se
. BMW original oilcoolers are ok, but not perfect.
The oil-temp gauge is there, not only for our curiosity, but to give us a warning when it is high time to stop the engine and let it cool!
Added cooling of the engine is a good idea. I have thought about installing a radiator fan. Friend of mine have a tube-fan that he turns on in traffic jam.
they have several solutions for different conditions. www.sjbmw.com
carry the solutions that CC developed; you need to ask for Chris.
You could ask Terry Phillips what stuff he still carries: http://www.suburban-machinery.com/
He had an oilfilter relocation kit that is really neat.
Synthetic or not... if the temp hits 180'C - it will not last long, no mattter which oil. Omega 757, http://www.magnagroup.com/
,lasted about 5000km before the oil-pressure started to drop. And at about 15000km it hit 3-4 bars operational pressure... way too low... all other oil, that I have tested reached 4 bars before 3000km...
- high engine temps = change engine oil often. When operation pressure drops below 5 bars - the oil should have been changed at 6 to 5.5bars...
(this applies for 0W-40, 0W-60, 15W-40, 20W-50; if you run on 30W it may be different; I haven't tested to drive on thinner viscosities).