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Topic-icon 76 R90S oil pressure light problem

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1 year 3 months ago #3880 by 12763
76 R90S oil pressure light problem was created by 12763
I have a 76 R90S with 65,000 miles on it. Just restored it cosmetically after purchasing from a friend. Bike cranks and runs out fine but after it warms up the oil pressure light comes on at idle (1000 - 1,500rpm) It goes out around 1,500 - 2000rpm. The previous owner had noted this issue and had already checked the sump/scavenger and changed the oil pressure switch to no avail. Oil pump looked fine. It has fresh oil (10w-40) and oil filter(BMW).
Any thoughts on where I should go from here?

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1 year 2 months ago - 1 year 2 months ago #3909 by Wobbly
Replied by Wobbly on topic 76 R90S oil pressure light problem
► 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. :P

Hope this helps.

Don't hide 'em, Ride 'em !!
#15150
Last edit: 1 year 2 months ago by Wobbly.

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1 year 2 months ago #3910 by 12763
Replied by 12763 on topic 76 R90S oil pressure light problem
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.

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1 year 2 months ago - 1 year 2 months ago #3911 by Wobbly
Replied by Wobbly on topic 76 R90S oil pressure light problem

Wobbly wrote: ► 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.

Don't hide 'em, Ride 'em !!
#15150
Last edit: 1 year 2 months ago by Wobbly.

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1 year 2 months ago #3918 by 12763
Replied by 12763 on topic 76 R90S oil pressure light problem
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.

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