Boxerworks.com

The factory rec'd covering the cooler in very cold weather on GS models without a thermostat
and used a differently sized orifice vs the RS & RT (with thermostat) to control cold oil flow.

A factory bulletin was issued on the early non-thermostat covers.
which says to inspect the small hole in that cover, and if 2.0 mm, to drill it to 4 mm.

"That is the bypass port hole, the function of which is to allow SOME oil to flow, even if cold.
Increasing the hole size reduces the amount of oil passing through the cooler.
Speculation is that with the original smaller hole, some coolers ruptured with starts in quite cold weather
from the VERY high oil pressure when the oil is very cold.
That hole is a bit smaller in diameter than the hole in the thermostatic type covers
(which is, as noted well above, about 8 mm)
The GS cover does not have a thermostat.
It uses that specific internal hole size to ALWAYS allow some oil to flow,
and as the oil thins from heating up, more oil flows.
As noted above, the EARLY GS covers had a too-small hole, and it needs drilling..."
~ bmwscotter

ME 109 wrote:Oi! where did yer post go Vanzen?

My point stating the obvious is to do with all the talk past and present, about oil coolers.
Which amounts to nothing, if the thermostat doesn't work.
Which is part of the discussion that never really gets consideration.

To state: 'a thermostat that doesn't work is not much use at all'
may be more or less true or not.
Perhaps dependent upon the consequences of 'doesn't work',
i.e. whether the thermostat is stuck open or closed.
If closed – the thermostat and the cooler are certainly not useful, but still do no harm.
The engine is cooled just as if no cooler were attached.
If open – then the cooler functions quite like a GS non-thermo cooler,
with the important exception that the rate of oil flow vs temperature will be changed
due to the larger orifice -
and this might be useful – if duly considered.

My assumption will be that the factory engineers ultimately justified the additon of a cooler,
and especially as engines gained displacement and were required to burn leaner & hotter in the later years,
with the educated decision that an oil cooler would be a beneficial addition
to assure that the antiquated air-cooled engine could operate within it's prescribed temperature range
and therefor maintain engine longevity expectations ...
esp. considering those applications involving:
1. faired 247s that would have limited air-flow across the engine, and
2. 247s that were subjected to the rigors and abuse of off-roading.

Otherwise the added production costs of fitting a cooler
never would have passed by the desks of the bean-counters.

The proposition,
'The old airheads never had a cooler, the newer ones shouldn't need one either'
patently discounts changes made to the machine and the ulterior demands made upon it
during it's relatively short span of time and production.

vanzen@rockerboxer.com wrote:To state: 'a thermostat that doesn't work is not much use at all'
may be more or less true or not.

I should have been more to the point and said a thermostat which does not work because, no oil flows through it, because the expanding elephant element is kaput.
From what I can tell, it is unlikely that a thermostat could be 'stuck open' unless deliberately held open by a longer bolt in the bottom of the thermostat, which holds the piston? open.

ME 109 wrote: From what I can tell, it is unlikely that a thermostat could be 'stuck open' unless deliberately held open by a longer bolt in the bottom of the thermostat, which holds the piston? open.

I would have to guess: "unlikely," yes, but hardly impossible.

The unit functions in exactly the same way as an automobile coolant thermostat, and they fail in the "closed" mode the great majority of the time, but I've had them fail in the "open" mode from time to time as well, so I'm guessing that the oil cooler thermostat would be the same.

I think the only way the piston could be stuck in the 'open' position is if the pin in the expanding element got stuck.
There is a fairly beefy spring to push it closed.

ME 109 wrote:

Have you replaced the element in yours?

No I haven't Doug, I believe the part is still available from motobins.
I usually just put a longer bolt in the bottom of the thermostat in summer.
You can see the silver pin sticking out a little from the wax filled brass cartridge. As the oil increases in temp, so does the wax which pushes the pin out and pushes the piston up and aligns the 'ports' allowing oil into the radiator circuit.
It makes sense to me that the oil flow into the cooler is variable, as in x temp = x alignment of ports, up to full alignment.

Edit, gotta scratch my head a bit here, from memory the cartridge goes up inside the piston, with the pin facing downwards. The pin contacts the end of the standard 10mm long bolt that goes in the bottom of the thermostat.

ME 109 wrote:No I haven't Doug, I believe the part is still available from motobins.
I usually just put a longer bolt in the bottom of the thermostat in summer.

You could have a summer bolt, a winter bolt, and a spring/fall bolt.

dougie wrote:You could have a summer bolt, a winter bolt, and a spring/fall bolt.

That would work well Doug, but I'd need the winter bolt for early summer days, followed by the spring bolt by about morning tea time, and then the summer bolt about lunch time.
Unless of course the day was going to be a scorcher, then I would have the summer bolt in by breakfast time.