11 BMW 1983 R100RS Diagnose Intermittent Low Oil Pressure Light

This write-up covers a journey of how I isolated problems in the oil system of this bike when my low oil pressure light came on. I diagnosed and fixed a couple problems in the engine oil system. But I’m not absolutely certain I have found the problem causing the low oil pressure light to come on. I’ve ruled out failures in the engine oil system and am convinced the oil pump is working properly, the engine oil passages are not blocked, the oil seals are not leaking, the oil pickup and screen are okay and the oil level is correct.

The electrical circuit is now the most likely reason for the intermittent low oil pressure light coming on. The last thing I replaced is the oil pressure sender switch even though when I originally tested it, it worked. But, it’s the next most likely component to have a problem due to its mechanical action. Until I ride a couple hundred miles, I won’t draw a final conclusion about having fixing the problem.

References

These references were very helpful to me as were replies to some posts I sent to the Micapeak Airheads forum. In particular, Bob Fleischer, Tom Cutter, Anton Largiader and Mike Valenti provided answers and assistance that were very valuable to me both on the forum and in private emails.

Parts Used

These are the parts I used for fixing the various problems I found,

Part Number Description Qty
11 11 1 250 157 BLIND PLUG – M12X1,5 (to 02/85) 1
11 11 1 250 159 COMPRESSION SPRING – L=11MM (to 02/85) 1
11 42 1 264 160 SHIM – 44X4 2
11 42 1 337 098 RING – 44X4 1
11 42 1 337 575 OIL FILTER OIL COOLER 1
 61 31 1 243 414 OIL PRESSURE SWITCH – M12 X 1.5 1

The Red Light Comes – Oh [email protected]#T!!!!

Since I got this bike running a month ago, I’ve been taking short trips with it so I can have some confidence it is reliable. I was riding along at about 50-60 MPH on a 93 F day when all of a sudden, the red oil pressure warning light came on just as I turned on to the road to my house. I immediately hit the kill switch, pulled the clutch and pulled over to the side of the road. I waited for a minute and then started the bike again. The oil pressure light went out immediately. Hmm.  I started riding and about two minutes later, the warning light came on again.  So, I went through the same drill of immediately stopping the engine and waiting for a bit. On start up, the oil light went out immediately.  This time I made it home just as the light came back on.  Not a good sign.

Some History

When I did the major service on the bike and changed the oil and filter, I found that the large white o-ring, aka, the infamous $2,000 o-ring, was torn and there was no metal shim behind it. I called the fellow I bought the bike from and asked more about what he had done to service the bike after he bought it. The original story was he bought it for his girl friend, but it was too big for her so it sat about a year before they decided to sell it. On our call, he told me he did no service work on the bike, nor did it get ridden except for a short ride home. His girl friend sat on it and decided it was just too big for her. The fellow he bought it from said it had been sitting for four years (and I can believe that due to the crud and rust on the frame) but he had changed the oil just before he put it up for sale. Perhaps he is the one who bungled the oil filter replacement and left out the shim?

At that time, I measured the distance between the edge of the filter canister and the top of the  engine block with a depth gauge (see picture below between the red lines). I got about 3.5-3.6 mm.

Distance to Measure From Edge of Filter Can to Top of Engine Block

Distance to Measure From Edge of Filter Can to Top of Engine Block

Based on the information in Bob Fleischer’s web page and this measurement, I added one shim behind the new white o-ring and called it good.

Potential Causes

Some potential causes for the low oil pressure light coming on are:

  • Low oil level in the oil pan
  • Oil pickup inside the oil pan lose or fallen off
  • Oil sender switch failed
  • White o-ring torn or distorted. Perhaps I munged the white O-ring when I installed it?
  • Oil pump worn or leaking badly
  • High oil pressure relief valve stuck open
  • Really bad engine seals and/or main bearings resulting in lost pressure

Below are the ones I looked into and my conclusions.

Oil Level and Oil Pickup Check

A quick check of the dip stick showed normal oil level in the pan. During the earlier major service, I removed the oil pan and replaced the pan gasket. I checked the oil pick up bolts and the oil pick up screen.  The bolts were tight and the screen did not have any sludge or gunk build up. There were no metal shards or other material in the bottom of the pan. I’m going to assume for now that the oil pickup is not causing the problem since it was good when I inspected it.

Oil Pressure Sender Switch Test

It’s very easy to remove the oil pressure sender switch from the left side engine block. It’s right behind the carburetor. I used a 24 mm socket and it came right out. Note that a standard socket is too shallow to go completely over the lug on the end of the switch. But, if I push the socket on over the switch about half-way over the face of the bolt surface and then push the shaft of the socket extension into the socket, it bites enough of the nut to loosen the switch body. The switch has a copper or aluminum washer to help seal it. That washer should be replaced when you reinstall the sender unit. It’s sold with a new switch, but part number 07-11-9-963-132 is the same washer.

This short video shows how I tested the oil pressure sender switch.

Testing Oil Pressure Switch

The oil pressure sender tested good, so it doesn’t seem to be the cause.

Checking Oil Filter Canister Depth and White O-Ring

The next step is to pull the oil cover off, check the white o-ring and remeasure the distance between the top of the oil filter canister and the top of the engine block. I remove the front lower fairing panel. I decided to remove the exhaust system as well so I can clean it up a bit as it’s grungy. That will make it easy to remove the three bolts holding the oil filter cover. As this bike has the oil cooler, there is not a lot of room to get to those three bolts.

When I removed the cover, the white o-ring was not damaged. That’s good. Then I measured the distance from the top of the oil filter canister to the top of the engine block. In the picture below, you can see the edge of the oil filter canister is below the top of the engine block. By the way, there are two styles of canister, earlier ones like mine with a sharp edge and later ones with a rolled edge. The metal shim is important with sharp edge canisters since it protects the white o-ring from being cut when the oil filter cover is bolted onto the engine block.

Canister Has Sharp Edge

Canister Has Sharp Edge

The distance I measure is shown by the red line.

Distance to Measure From Edge of Filter Can to Edge of Engine Block

Distance to Measure From Edge of Filter Can to Edge of Engine Block

Once again, I used a depth gauge as the flat edge let me get it square with the top of the engine housing.

Keep Depth Gauge Parallel to Engine Block When Measuring

Keep Depth Gauge Parallel to Engine Block When Measuring

To my eye, it looked about the same as the first time I measured it. But, the graduations are only 0.5 mm so it’s a bit coarse for these measurements.

Depth Gauge Shows About 3.6 mm

Depth Gauge Shows About 3.6 mm

So I used my vernier caliper to more accurately measure the depth shown on the depth gauge.

Vernier Caliper and Depth Gauge

Vernier Caliper and Depth Gauge

Using Vernier Caliper to Transfer Depth Gauge Measurement

Using Vernier Caliper to Transfer Depth Gauge Measurement

I made several measurements since it’s hard to keep the depth gauge parallel to the engine block and accurately transfer the depth to the vernier caliper. With this technique, I measured 3.8 to 3.9 mm canister depth depending where around the circumference of the canister I took the measurement.

Vernier Caliper Reading 3.82 mm Canister Depth

Vernier Caliper Reading 3.82 mm Canister Depth

Well, that’s interesting. Based on both Bob Fleischer’s and Anton Largiader’s information, it seems I should use two shims as my canister is set pretty deep as the design depth is 3 mm.

Oak Okelshen Formula for White O-ring Compression

Oak Okelshen wrote an article in the Airhead newsletter, Airmail, on how to compute the compression of the white o-ring when using shims and the optional paper gasket. Mike Valenti sent me this information in a private Email. Based on Oak’s formula, I’m at the lower range of o-ring compression, so again, adding two shims makes sense
Variables 
O-ring diameter -> “O” = 4.0 mm (I measured this because I’m a skeptic)
Shim Thickness -> “S” = 0.3 mm (I measured this as there nave been variations)
Cover Gasket Thickness -> “C” = 0 mm (almost never used)
Gap between canister and top of engine housing -> “G” = 3.85 (average)
Equation 
[(O + S – C – G)/O ] * 100% => between 10% – 25%
For my canister with one shim:
[(4 + 0.3 – 0 – 3.85)/4.0 * 100% = 11.2%
This is too low for my taste.
For my canister with two shims:
[(4 + 0.6 – 0 – 3.85)/4.0 * 100% = 18.8%
This seems to put the o-ring compression in the middle of the range.

Oil Filter Inspection

I pulled the oil filter out, I let it drain overnight.

Draining Filter Cartridge

Draining Filter Cartridge

After the filter had drained, I slit the outer cardboard cover and removed it. I have the hinged filter used with the oil cooler.

Hinged Oil Filter-Left Outside End; Right Next to Engine End

Hinged Oil Filter-Left Outside End; Right Next to Engine End

Cutting Outer Paper Cage

Cutting Outer Paper Cage

This exposes the filter paper.

Outer Paper Cage Removed Exposing Filter

Outer Paper Cage Removed Exposing Filter

I tried to pry the metal ends of the filter off the paper, but that didn’t work. So I just cut the paper away from the metal ends. That’s much simpler.

Cutting Filter Paper Cylinder From Metal End

Cutting Filter Paper Cylinder From Metal End

Filter Paper Cylinder Removed from One Half of Filter

Filter Paper Cylinder Removed from One Half of Filter

I kept kept track of which paper goes with which half of the filter, the inner half or the outer half. I unfold the filter paper and inspect it on both sides. These videos show what I saw.

Filter Paper Analysis-Outside 1/2 of Cartridge

Inside Half of Filter (Next to Engine)

Filter Paper Analysis-Inside 1/2 of Cartridge, Next to Engine

Outside Half of Filter

Here are some close up pictures of some of the debris trapped in the filter.

Black Plastic-like Particle

Black Plastic-like Particle

Bright Metal Particles

Bright Metal Particles

Bright Metal Particles

Bright Metal Particles

I posted the videos and pictures to the micapeak Airheads forum asking for comments about what I found. The opinion was that this amount of debris was not alarming.

Based on the black plastic, I will replace the cam chain tensioner when I do the restoration. As mentioned in one of the videos, none of the bright particles are magnetic, so likely they are aluminum. Later I found a likely source for the aluminum bits.

Checking Oil Filter High Pressure By-pass Valve

A comment from Anton Largiader about checking the oil filter high pressure relief valve altered me to the fact its a potential failure point in the lubrication system. Its job is to prevent lack of oil flow should the oil filter get clogged, or collapse. If that happened oil flow is restricted and the motor can be damaged. To prevent this, a ball valve at the back of the oil filter canister opens when the pressure inside the canister gets too high. However, if that valve fails, then unfiltered oil gets into the engine which is not good.

You can see the slotted end cap that traps the ball and spring of the valve inside the red oval in the picture below.

Filter Canister High Pressure By-Pass Valve

Filter Canister High Pressure By-Pass Valve

To my untrained eye, it doesn’t look right as the cap screw appears distorted. I put a wide blade, long handle screw driver in the slot on the top of the cap screw and find I can wiggle the cap easily. And then it falls out completely. The cap is not magnetic so I can’t use my magnet to fish it out, so I use my part grabbing tool. The ball bearing and spring come out with the magnet.

High Pressure By-pass Valve Parts-Mangled and Bent

High Pressure By-pass Valve Parts-Mangled and Bent

Mangled Aluminum Cap Screw-Source of Aluminum in Oil Filter?

Mangled Aluminum Cap Screw-Source of Aluminum in Oil Filter?

Mangled Aluminum Cap Screw

Mangled Aluminum Cap Screw

The cap screw has become oval. It’s made out of aluminum. My hypothesis is it got loose in the steel threads of the filter canister and through vibration worn into an oval shape. This could explain the bright aluminum bits I found in the oil filter.

The spring is not broken, but this does happen and that’s bad as hard bits of the spring can go through the oil system and damage crank journals, the oil pump and potentially restrict oil flow in the engine oil passages. But, the spring is not straight, likely due to the cap screw getting cock-eyed in the screw threads putting uneven pressure on the spring. I’m very glad I found this. But, I should have found it when I changed the oil and filter during the major service, but I didn’t know about the valve then. Now I do.

Here is how the parts go together with the wide part of the spring against the back side of the hole in the canister and the cap screw facing the outside of the cannister. It looks like a leaning tower of Pizza 🙂

Spring, Ball and Plug Assembly Order (Bottom-Inside; Top-Outside)

Spring, Ball and Plug Assembly Order (Bottom-Inside; Top-Outside)

I ordered a new cap screw and spring. You can see the difference between the new spring (left) and the original one (right). The original has sagged quite a bit. And, the new cap screw (left) is actually round 🙂

New (Left) and Original (Right) Relief Valve Spring

New (Left) and Original (Right) Relief Valve Spring

New (Left) and Damaged (Right) Aluminum Cap Screw

New (Left) and Damaged (Right) Aluminum Cap Screw

Install Filter Canister High Pressure By-pass Valve

It’s dark and a long way inside the canister to get to the hole for the by-pass valve. I decided to let gravity be my friend. Let Gravity Be Your Friend

Yes, I forgot to remove the tank, even though I had removed the fuel lines from it in preparation. It quickly came off as fuel was accumulating under the bike … DUHOOOO !!!

I originally tried my magnet to hold the spring and ball bearing together so I could insert them into the hole. But the magnet is too strong and there was no room to put a screw driver inside the canister to hold them there as I removed the magnet.

Magnetic Pickup is Too Strong

Magnetic Pickup is Too Strong

I used my parts grabber to insert the parts. First the spring goes in, wide part to the back of the canister and then the ball bearing on top of the spring.

Parts Grabber

Parts Grabber

Parts Pickup Holding Relief Spring-Small Coils Face Outward

Parts Pickup Holding Relief Spring-Small Coils Face Outward

Parts Pickup with Ball Bearing

Parts Pickup with Ball Bearing

Fishing Ball Bearing Into Hole

Fishing Ball Bearing Into Hole

Now the fun part begins. The ball bearing is almost to the top of the screw threads in the hole as you can see in the picture below.

Ball Sitting On Top of Spring

Ball Sitting On Top of Spring

I use a wide blade screwdriver that has a thick enough blade to capture the cap screw. The blade shown below is thick enough, but too narrow. I tried my Craftsman screw driver with the widest blade and it was exactly the right width and blade thickness so the cap screw would not fall off the blade.

A Bit Wider Blade Will Work Better

A Bit Wider Blade Will Work Better

I wasn’t able to get the cap screw to thread. It’s possible that the steel threads are bunged up a bit from the old cap screw rattling around. I removed the ball bearing and spring and carefully screwed the cap screw into the threads until it got hard to thread, backed it out and then screwed it back in a bit more. This seemed to dress the steel threads enough to let me screw the cap screw in until it is flush with the end of the canister. I checked the threads in the aluminum cap screw as I went and they were getting bunged up. Then I put the spring and ball bearing back into the hole and screwed the cap screw down. It only took about 5 tries to get the cap screw to screw in as its a tight fit and I have to get it perpendicular to the threads or it will cross thread. I aligned the slot in the cap screw with the groove cut in the back of the filter canister. That way when I check it during the next oil filter change, I can confirm that the cap screw has not rotated.

New Cap Screw Flush with Edge of Canister and Slot Aligned with Slot in Canister

New Cap Screw Flush with Edge of Canister and Slot Aligned with Slot in Canister

Some folks advise using a “tiny” bit of blue locktite to secure the cap screw, but be very careful to not get any on the ball bearing. Others advise peening the edge of the cap screw slot a bit to keep it from backing out. In my case, I did neither of these as the screw is nice and tight in the threads likely due to some minor buggering of the steel thread.

Install New Filter, Black Square O-Ring and White O-ring

I installed the black square profile o-ring inside the cover housing. I did not replace it as it’s new from the recent oil change

Black Square O-ring Installed in Cover

Black Square O-ring Installed in Cover

Then I install a new white o-ring outside the black square section o-ring.

White ($2,000 O-ring) Installed in Filter Cover

White ($2,000 O-ring) Installed in Filter Cover

I install a new oil filter with the built in black rubber gasket to the back of the filter canister.

Oil Filter Next To Engine HAS Rubber Gasket

Oil Filter Next To Engine HAS Rubber Gasket

The other end of the filter has no rubber gasket and faces me.

Oil Filter Outside End (Facing You) Does Not Have Rubber Gasket

Oil Filter Outside End (Facing You) Does Not Have Rubber Gasket

Oil Filter Installed Inside Canister-Shims Not Installed Yet

Oil Filter Installed Inside Canister-Shims Not Installed Yet

Next, I install two shims around the perimeter of the oil filter canister.

Two Shims needed for 3.8-3.9 mm Filter Canister Depth

Two Shims needed for 3.8-3.9 mm Filter Canister Depth

Two Shims Installed Between Canister Edge and Oil Filter

Two Shims Installed Between Canister Edge and Oil Filter

Then I carefully install the oil filter cover so I don’t disturb the white o-ring and attach the three bolts.

Oil Filter Cover Installed

Oil Filter Cover Installed

I concluded at this point that I found and fixed the problems that can cause the low oil pressure light to come on. I suspected my initial bad depth measurement lead to the white o-ring not sealing tightly so oil went straight to the sump on a hot day. I also fixed the filter canister high pressure by-pass valve which could allow unfiltered oil to go through the engine. Since the oil going through the by-pass valve still goes to the engine, I am not convinced it would cause a low oil pressure condition.

I plan to measure the oil pressure with an oil pressure test gauge at Harbor Freight to see how much pressure the bike produces, but first, I have to install the exhaust system.

Install Exhaust System

I was glad I remove this and the lower right side fairing panel. I needed all the room I could get to fix the filter canister high pressure by-pass valve. I also cleaned up the exhaust system. But, it is badly rusted and pitted, so I know I will need to replace it when I do the restoration.

Cleaned Up Exhaust

Cleaned Up Exhaust

Cleaned Up Exhaust

Cleaned Up Exhaust

I use some anti-seize on the header pipe where it inserts into the head, on the threads the header nut screws onto and on the cross-over pipe where it fits over the header pipes. The cross-over pipe was so badly rusted, I replaced it with a used one from my R75/6 project for now.

Anti-Seize on Exhaust Spigot Threads

Anti-Seize on Exhaust Spigot Threads

Anti-Seize on Header Pipe

Anti-Seize on Header Pipe

There are two steel rings that go inside the header pipe nut to seal the exhaust pipe to the header.

Header Pipe Rings Seal Header Pipe to Head

Header Pipe Rings Seal Header Pipe to Head

The square cross-section ring goes against the inside of the header nut and the beveled cross-section ring with the split in it fits inside the square cross-section ring into the side with the matching bevel. As shown below, the square ring on the left goes against the inside of the header nut with the bevel side facing you.

Solid Ring Goes First-Bevel Side Faces You

Solid Ring Goes First-Bevel Side Faces You

Tapered Ring with Cut Goes Last-Flat Side Faces You

Tapered Ring with Cut Goes Last-Flat Side Faces You

When I insert the header pipe into the head, I rotate it up and down to distribute the anti-seize around the pipe.

Wiggle Header Pipe to Distribute Anti-Seize

Wiggle Header Pipe to Distribute Anti-Seize

Wiggle Header Pipe to Distribute Anti-Seize

Wiggle Header Pipe to Distribute Anti-Seize

I remove the headers and dry fit them into the cross over pipe. I insert the cross-over tube on the stub of the header pipe that also has some anti-seize on it. I don’t tighten the bolts on the cross-over pipe yet.

Anti-seize on Header Stub to Cross Over Pipe

Anti-seize on Header Stub to Cross Over Pipe

Header Assembly with Cross-Over Pipe Loosely Connected

Header Assembly with Cross-Over Pipe Loosely Connected

Then I insert both header pipes into the heads getting them all the way inside the heads and spin the header nut a few turns to hold them there, but don’t tight it yet. I adjust the cross-over pipe so it’s even on the stubs of the header pipe.

Header Nut Loosely Threaded

Header Nut Loosely Threaded

Cross-over Pipe Even on Header Pipe Stubs

Cross-over Pipe Even on Header Pipe Stubs

I insert the header pipe hanger bracket onto the header pipes along with the muffler clamps. Then I slip the muffler onto the header pipe.

Muffler to Header Clamp Bracket

Muffler to Header Clamp Bracket

Now, I screw in the allen bolts that secure the rear muffler bracket to the frame. I tighten these down to secure the muffler.

Attaching Rear Muffler Bracket with Allen Bolts

Attaching Rear Muffler Bracket with Allen Bolts

Now I install the other muffler the same way. I use my exhaust nut wrench (not shown) and tighten the exhaust nuts. I don’t get aggressive with these. I snug them up and then lean on the wrench for another 1/8 turn.

I tighten the muffle clamps and then then header mounting brackets which hang on the rear engine mounts. I torque these engine mounting nuts to 55 Ft-lbs.

Testing Oil Pressure

I bought an oil pressure test gauge at Harbor Freight. It comes with 11 brass adapters to fit most threaded holes you find for oil pressure and transmissions. Some are tapered pipe thread and others are straight thread. The /5 used a tapered pipe thread but this bike has straight threads as shown in the picture below.

Oil Pressure Test Kit-Harbor Freight

Oil Pressure Test Kit-Harbor Freight

Correct Thread Adapter

INCORRECT Thread Adapter-USE THE STRAIGHT THREAD.

I thread the adapter where the oil pressure sender went on the left side of the engine block behind the carburetor.

Adapter in Oil Pressure Sender Hole

Adapter in Oil Pressure Sender Hole

Hose Attached to Adapter

Hose Attached to Adapter

I screw the hose from the gauge into the adapter.

I put the gauge near the instrument cluster so I can watch both RPM and oil pressure. Based on the oil system diagram from Bob Fleischer, the test gauge is before the high oil pressure relief valve above the timing chain (#11 in his diagram). That means I should see higher oil pressure than the 75 PSI set point of the relief valve. And, the pressure should be higher with cold oil than hot.

Here are two videos of the oil pressure I saw. CLICK TO PLAY THEM.

NOTE:
The red dash light the blinks on and off is the GEN light, not the oil pressure light. I’ll chase the cause down later.

Cold Engine Oil Pressure

Cold Engine Oil Pressure Test Video CLICK TO PLAY

Hot Engine Oil Pressure

Warm Engine Oil Pressure Test Video CLICK TO PLAY

I Think It’s Fixed

My conclusion at this point is I have plenty of oil pressure. I remove the oil pressure test gauge and install the original oil pressure switch with a new washer. But, to be sure everything is up to snuff, a test drive is in order.

My 130 Mile Test Drive

Yeah, I take long test drives since the Colorado Rocky Mountains are in my back yard. 🙂

Brook's Test Ride Route

Brook’s Test Ride Route – It Sucks, but Someone Has to Do it 🙂

Here’s the Google Map Route for those who want to take a nice ride along the Front Range mountains near Denver, CO.

For the first 80 miles there is no oil light coming on. I stop for some coffee at my favorite coffee shop  in Evergreen, CO overlooking the lake. And I head back home going down Turkey Creek Road, one of my favorites. And then, the oil pressure light comes on 🙁

This is a distinct bummer.  I immediately hit the kill switch, pull the clutch and pull over on the side of the road. I wait about 30 seconds, hit the starter and the engine fires up and the oil light immediately goes out. This happens about 5 more times until I get the bike back home. Something is still buggered somewhere.

I decide to install the test gauge and ride the bike until I can confirm I get low oil pressure, or I don’t.  With some wire and tape, I’m ready to see what the actual oil pressure looks like as I ride the exact same route again. Oh, the sacrifices you have to make to get good data 🙂

Connecting Test Gauge to Oil Sender Port

Connecting Test Gauge to Oil Sender Port

Attaching Oil Test Gauge to Instrument Cluster

Attaching Oil Test Gauge to Instrument Cluster

Oil Pressure Readings During A Test Ride

When I start out, I get similar pressure readings to my static cold start testing: as much as 100-110 psi at 4000-5000 RPM and 80 PSI at idle. When the bikes is hot, the pressure reads 34 PSI at 1000 RPM idle, 82 PSI at 3000, 88 PSI at 4000, 90 PSI at 5000-6000 RPM. If I grab a lot of throttle the pressure goes up to about 95 PSI +/1 as I pass 5000 RPM. If I gently accelerate to 5000 RPM it doesn’t go over 90 PSI. On uphill grades, the pressure is about 5 PSI lower and on down hill grades it’s about 5 PSI higher. I assume the oil level changes near the oil pickup so the head pressure in the inlet to the pump goes up and down causing a change in the oil pump outlet pressure.

BUT, at no time in 3 hours and 120 miles of riding in the mountains did I ever get low oil pressure. This rules out problems in the oil system itself including a bad oil pump, a stuck open high pressure oil relief valve, or engine seals leaking. So, the problem lies elsewhere.

Current Hypothesis of Intermittent Cause

I have an electrical problem in the oil pressure light circuit. All that’s needed for the low oil pressure light to come on is a ground to happen somewhere in the circuit. Since the pressure switch is mechanical, it’s possible it makes a momentary contact lighting the low oil pressure light. When I turn off the engine, the oil pressure goes down and the mechanical part inside the switch moves and clears the problem. So, I bought a new oil pressure switch and installed it. Time will tell if this resolves the problem of the oil pressure light coming on intermittently.

What’s Inside the Oil Pressure Sender Switch?

Since I have a new switch, I decided to open up the old one and see how it’s put together. This video shows how the switch is constructed and how it works.

Inside Oil Pressure Sender

Inside The Oil Pressure Sender CLICK TO PLAY VIDEO

Based on how the switch is constructed, one hypothesis is the plastic plunger that the small metal contact rides on top of can get worn enough that it rocks a bit to one side. The clearance between the small metal ring and the base ring is very small so a slight amount of tilting of the plunger may let it make contact. I can prove it, but a new switch removes the old one as a potential cause.

I’ll ride the bike and see if the low oil pressure light comes on again. If it does, then I will start looking for any place the oil pressure circuit can get a ground. But for now, I’m confident I do not have a low oil pressure problem in the oil system itself.

10 thoughts on “11 BMW 1983 R100RS Diagnose Intermittent Low Oil Pressure Light

    • Hi Skip,

      I’m pleased this material is helpful to you. Keep in mind there are changes in the oil systems between the /5 series and the later RS models. I think a number of the changes happened when the oil cooler was added. The fun I had with the $2000 O-ring is part of that “newer” oil system design. IMHO, its not an improvement in simplicity, reliability nor maintainability. But I suppose it’s a bit easier to work on than an in-line four UJM design of that era 😉

      Best.
      Brook.

  1. Very good article and well thought out. Good photos too! I have a 77 RS I bought new but have never had any real issues with it but your article is worth saving.
    Mac Morgan
    Hockessin, DE

    • Hi John,

      Thanks for dropping by. I hope you don’t run into similar problems. IIRC, the 1st year 1977 R100RS still used the same oil filter canister design found in the /6 models. IMHO< that's not as temperamental a design as the later models with the oil cooler and redesigned cover like I have on the 1983 model.

      Best
      Brook.

  2. Great stuff Brock, very helpful. The write up on the high pressure bypass valve was especially valuable as I’ve never seen that documented before. Three cheers!

  3. Thanks for a well written and documented article. I have a 84 R80RT.
    It has had the clock replaced with an oil press gauge.
    I was concerned about the high indications I saw (similar to what you show.)
    I did the same service you did, and found same results,
    IE cover had gasket when it should’nt, and blk. plastic bits in filter pleats.
    But the bike runs fine. And my oil pr. behaves just like yours in the vid.
    I suspect the design of the oil system creates higher pressure than I expected. My expectations may be not applicable as they are based on car or airplane engines. Thanks for all the info Mike

    • Hi Mike,

      Thanks for stopping by and reading one of my write-ups.

      I learned that “oil pressure” isn’t the constant we think it is. Not only does the pump vary pressure with RPM up to the point the high pressure relief valve starts opening, but the pressure will vary depending on where in the oil circuit you measure it. My pressure gauge was on the high pressure side of the high pressure relief valve, so I saw higher pressures than what maybe recorded on the other side of that valve.

      The bearing design for the engine will influence how much pressure the pump needs to deliver, so seeing what the manufacturer chose for bearing types can alert you to what the range of oil pressures the pump should deliver.

      I learned a lot working on this write-up.

      Best.
      Brook.

  4. Brook, was looking through this article. Two things I saw. First was that the Harbor Freight oil adaptor APPEARED to me to have a TAPER PIPE THREAD. BMW has two types of senders, the early /5 era, and all later ones.
    Taper threads….and Straight threads.

    The other thing, was the two photos of the pressure gauge ….looked like zero readings.

    • Hi Bob,

      Thanks for the review and comments.

      Yes, the caption needs to be edited on the adapter picture to indicate “INCORRECT” adaptor. Thanks for catching that. Yes, I used to incorrect pipe thread one to do the testing. Shame on me :-).

      The two “zero reading” pictures are actually videos as shown in the caption. You have to click to play them to see the readings. (I added that note to the caption). I can’t change the image selected for the thumbnail so it shows the first frame of the video with zero gauge reading.

      Thanks for looking this over. I appreciate it.

      Best.
      Brook.

Leave a Reply

Your email address will not be published. Required fields are marked *