► For the first year of ownership, I mistook the red alternator warning lamp for the orange oil pressure warning light when seen out the corner of my eye. Doesn't exactly sound like the case here, but just to be sure.

► I'd be running 20w50 in the summer. You can run 10w40 as a "winter weight" when temps dip on down. But for riding above 70°F, 20w50 is simply going to be a better choice. You'll want to run it under 3500 rpm for the first 3 miles for warm up, but 20w50 really is a better weight for air cooled engines in the summer.

► Consider replacing the oil pressure switch again. Go to your local auto parts store and get them to order you one. This switch was used on a great many German cars of the similar year, so finding one is going to be easy and cheap. Secondly, a different brand of switch is going to have a different actuation range that may stop this "nuisance" flickering.

► Lastly, check the condition of the oil by-pass ball and spring. Next time the oil filter is out, shine a light down in there. Deep at the end of the filter cavity is a spring loaded ball. Those springs give up with regularity at this age. If it needs replacement, then order the screw, the spring and the ball. You'll probably destroy all 3 getting the old parts out.

If there is really a question, then real answers can only be found with an actual pressure gauge, applied when the engine oil is warm (not hot; not cold). These type electrical switches are only good enough to be "indicators of a possible problem". We have to keep in mind that their nickname "idiot light" has some basis in fact. 😛

Hope this helps.

Made sure the filter was OK. Pressure release valve seems good - bearing/ball depresses and returns, dropped pan and checked pick-up - all good, re-installed with proper torque. No improvement. New sending unit switch should arrive today to try. It’s definitely the amber oil switch light. I’ll let you know if the new switch from EME takes care of it. If not I’ll set up a pressure gauge to check the actual pressures.

► I'd be running 20w50 in the summer. You can run 10w40 as a "winter weight" when temps dip on down. But for riding above 70°F, 20w50 is simply going to be a better choice. You'll want to run it under 3500 rpm for the first 3 miles for warm up, but 20w50 really is a better weight for air cooled engines in the summer.

This suggestion being placed #2 wasn't by accident.

Thanks Wobbly,
Replaced the oil sender switch but that didn't do it either. So, I've covered the most likely offenders. Next, I'll get that oil pressure gauge and see what the readings are.
On a trip for the next week so it will be a week or so before I can sort out the actual pressures.

Posted by: @wobbly

► For the first year of ownership, I mistook the red alternator warning lamp for the orange oil pressure warning light when seen out the corner of my eye. Doesn't exactly sound like the case here, but just to be sure.

► I'd be running 20w50 in the summer. You can run 10w40 as a "winter weight" when temps dip on down. But for riding above 70°F, 20w50 is simply going to be a better choice. You'll want to run it under 3500 rpm for the first 3 miles for warm up, but 20w50 really is a better weight for air cooled engines in the summer.

► Consider replacing the oil pressure switch again. Go to your local auto parts store and get them to order you one. This switch was used on a great many German cars of the similar year, so finding one is going to be easy and cheap. Secondly, a different brand of switch is going to have a different actuation range that may stop this "nuisance" flickering.

► Lastly, check the condition of the oil by-pass ball and spring. Next time the oil filter is out, shine a light down in there. Deep at the end of the filter cavity is a spring loaded ball. Those springs give up with regularity at this age. If it needs replacement, then order the screw, the spring and the ball. You'll probably destroy all 3 getting the old parts out.

If there is really a question, then real answers can only be found with an actual pressure gauge, applied when the engine oil is warm (not hot; not cold). These type electrical switches are only good enough to be "indicators of a possible problem". We have to keep in mind that their nickname "idiot light" has some basis in fact. 😛

Hope this helps.

Hey Richard @wobbly

What a great post.  I thought I too had an oil pressure issue... and spent time diagnosing and documenting my results--going as far as purchasing an oil pressure gauge/kit... THEN, on my final check of the GEN/OIL dummy lights, I REALIZED that You Were Correct! 😋   I too had been mistaking the red GEN light for my red OIL light (both are Red on my '81 RS) haha. 

Soooooo... I'm relieved that one problem (I thought I had) has been alleviated from my list.  Now on to figuring out why my GEN light illuminates at times.

Thank you both  for this post.  Truly helpful  😎 

-Adam

'81 R100RS Silver Smoke

Ps. Hey @12763 what was the final verdict on your troubleshooting?  I don't think I saw any final post/resolution.  Cheers.

The location of the oil filter by-pass ball valve....

More and more of these are having issues as the spring collapses/breaks after 40 years of service. 

?1

The collapsed and/or broken spring is on the Left; the new spring for comparison on the Right.
The screw cap and ball which sit on top of the spring also shown.

Testing the condition of the spring is easy. While the oil filter is removed, simply reach to the bottom of the oil filter housing and push on the ball through the oil orifice in the screw cap. You'll need a slender rod to enter the small opening in the cap. I use an old bicycle spoke. You should feel the ball give way under pressure and then pop your tool back out. If you do not detect this "spring action", then you MUST replace all 3 parts: cap, spring and ball. 

Hope this helps.