1987 K75S that had been sitting for 20+ years, but put away well..
Currently 109,000 miles with a major rebuild/parts upgrade at 103K in the late 1990s.

for the past couple hundred miles I have been seeing the oil light flicker on when hot and pulling away 1st gear from a traffic light after sitting for a bit. no oil light at any other time.

I got the bike running over the winter including an oil change using 20W50 regular oil,
and currently have about 1500 miles on it since.

Oil level is fine.. just above the center dot and still looks clean.

Any ideas on what to look at?

Ernesto wrote:1987 K75S that had been sitting for 20+ years, but put away well..  
Currently 109,000 miles with a major rebuild/parts upgrade at 103K in the late 1990s.

for the past couple hundred miles I have been seeing the oil light flicker on when hot and pulling away 1st gear from a traffic light after sitting for a bit.  no oil light at any other time.

I got the bike running over the winter including an oil change using 20W50 regular oil,
and currently have about 1500 miles on it since.

Oil level is fine.. just above the center dot and still looks clean.

Any ideas on what to look at?

A flickering oil warning on the dash means low oil pressure. Don't continue to run the engine. Detemine if the oil pressure switch is faulty (at the front beneath the water/oil pump) Don't confuse it with the oil temp sensor if your bike is qauge equipped. Look for water in the engine oil. Is the water pump/oil pump seal set leaking?

Drop the oil pan and clean the oil pickup screen, but also determine if the oil pickup tube o-ring or gasket is dislodged or not in place. What is the age/condition of the oil filter? A cheap brand, not specified to the bike?

Who did the 'major' work a mere 6,000 miles ago?

Your signature line doesn't indicate the model specifics. This is the Lufty turbo bike, yeah? That's a whole nother nether region.

Check the oil feed hose connections to and from the turbo and any oil cooler which may have been added due to the inevitable increased heat stresses placed on the engine from the turbo doing its job.

A flickering oil warning on the dash means low oil pressure. Don't continue to run the engine. Detemine if the oil pressure switch is faulty (at the front beneath the water/oil pump) Don't confuse it with the oil temp sensor if your bike is qauge equipped. Look for water in the engine oil. Is the water pump/oil pump seal set leaking?

Drop the oil pan and clean the oil pickup screen, but also determine if the oil pickup tube o-ring or gasket is dislodged or not in place. What is the age/condition of the oil filter? A cheap brand, not specified to the bike?

Your signature line doesn't indicate the model specifics. This is the Lufty turbo bike, yeah? That's a whole nother nether region.

Thank you!!
I will start digging in to see what is going on..
I do not have an oil temp gauge..
Oil filter was a name brand/quality filter.
Bike does have lots of Luftmeister and other new (1990s) internals (I can include a parts receipt if it will help) but no turbo..

Just FYI if it helps..

This was the last major work receipts from the original owner with the engine upgrade in 1999.. the bike was only run a couple thousand miles after that and then stored away for 20+ years

I had a Guzzi that did that (V1000G5). Turned out to be a corroded oil pressure switch and as your K-bike has been standing for so long, I'd go for that as the cheap option first. It could also be corrosion on the spade terminal that connects to the pressure switch.

I had a Guzzi that did that (V1000G5). Turned out to be a corroded oil pressure switch and as your K-bike has been standing for so long, I'd go for that as the cheap option first. It could also be corrosion on the spade terminal that connects to the pressure switch.

Thanks.. will check it out.. I only get it flickering on when accelerating from 1st gear after sitting at a stop when it is hot.

I'll do an early oil change as well.. everything was super clean on the initial change

If you find the oil pressure switch is faulty, it is OEM BMW part number 12 61 1 277 642, and fits many different years and model BMW motorbikes (all early Ks, including K1200 bricks, and all R1100 (not R1150 or Hexhead) Oilheads, as well as some BMW cars - E28 series 518, 1980 - '87 and E30 series 316, 318, 320, 1982 - '94. This makes ordinary parts store searches easier.

Of course, in many cases, it is simply whether the perfectly acceptable range of the replacement switch has a spade or mushroom head connector atop it. That's research for the end user.

Two Wheels Better wrote:Of course, in many cases, it is simply whether the perfectly acceptable range of the replacement switch has a spade or mushroom head connector atop it. That's research for the end user.

Makes no odds A female spade terminal will still grip a mushroom-head oil pressure switch but you might need to squeeze the spade terminal slightly with a pair of pliers to increase the grip. All three of my Bricks have been growing mushrooms down there.

Dai wrote:

Two Wheels Better wrote:Of course, in many cases, it is simply whether the perfectly acceptable range of the replacement switch has a spade or mushroom head connector atop it. That's research for the end user.

Makes no odds A female spade terminal will still grip a mushroom-head oil pressure switch but you might need to squeeze the spade terminal slightly with a pair of pliers to increase the grip. All three of my Bricks have been growing mushrooms down there.

Of course, my caution was not the basic connection, but that the switch was within acceptable range for reading a brick's oil pressure correctly. I happen to know that a 2002 Bimmer's op sw works a charm.

Snuck out to the garage to take a peek since I havent paid attention to the switch before..

it has a bit of road grime, but visually doesnt look bad. Looks like I am missing a rubber cover for it.

Does your bike have LED idiot lights in the instrument cluster?

My old K75RT had LED's and when riding in the rain my oil pressure idiot light would come on and stay on until the engine dried out.  The little bit of current leakage through the crap on the switch can be enough to make the light come on.

Clean the switch body and spray it with WD40.

Does your bike have LED idiot lights in the instrument cluster?

no.. no LEDs in this one (I did install a Katdash and other bulbs in my 74 R60/6)

I only get the light flicking on when pulling away from a traffic light when hot.

When you read my guess your going to say, that's a ridiculous case of wishful thinking, and I'll agree, but that hasn't stopped me in the past.

Although it was many years ago, it wasn't many miles ago that there was major engine work done. When you take off from stationary in first, the oil lurches to the rear, once moving, not so much, I think. Spose an oil cleaning rag was mistakenly left in the engine (or a plastic glove) and it's now worked it's way to the bottom of the sump, in front of the pick up filter. You stop at a red light, it settles, you take off, it lurches rear and gets partially sucked up, you back off, going into second, it settles.

Is this likely? No.
Is it ridiculous? Yes.
Have I ever heard of this before? No
Would I give it a shot? Yes.

I hope it's the case, cause it's an easy fix, remove the oil filter and you might get your hand in there.

At least it matches the symptoms, I think.

Ernesto wrote:Looks like I am missing a rubber cover for it.

It also looks like the PO had a corrosion problem with the spade terminal as that - thing - is a replacement (I hate those pre-insulated terminals with a real passion). The cover has a hole just wide enough to get the wire through, so you'll either have to live with the setup as it is or chop the terminal off, fit a cover and then crimp another terminal on. Before you chop it off, pull gently on the wire to see if you have sufficient slack to cut and crimp. If you don't, you actually really do . The wire is brown/green and if you check under the tank, somewhere close to the HES connector will be a single-way connector for the oil pressure switch. Take the HES cover off the crankcase and you'll find the wire is clipped in to the vertical channel. Ease it out of the channel and pull some of the excess through.

I'm betting though that the wire is perished and brittle underneath the engine. In this case cut off the one-way terminal and solder a new wire to the top of the old one. Use it as a pull-through; alternatively it is possible to feed a new wire through the pump body from the HES housing. One of two things will happen; the wire will happily pop out through the bottom of the pump body or the bloody thing will catch and curl up in the recess in the bottom of the pump body. A pair of longnose needle pliers and a torch (flashlight) are a good combination to pull the damn thing out. There's plenty of room to work in the recess. You can't get a single-way OEM-type connector easily, so I've used 'Japanese' (3.6mm) bullet terminals as a subsitute.

On the EME website under water/oil pump they have the sensors on special for $11, usually $13 and the rubber boot that fits over the connector is next to it for $10.  The sensor comes with its own washer.

Point-Seven-five wrote:Does your bike have LED idiot lights in the instrument cluster?

My old K75RT had LED's and when riding in the rain my oil pressure idiot light would come on and stay on until the engine dried out.  The little bit of current leakage through the crap on the switch can be enough to make the light come on.

Clean the switch body and spray it with WD40.

Of all of the dozens of K bikes I've owned with LEDs that's only happened on one of them. It was a 93 K1100LT and in heavy rain the oil light LED would come on but very dimly. I tried replacing the oil switch wire but that did not fix the issue.

Duck,in my case it was the mix of road dirt and winter salt coating the switch under the connector boot that when wet became just conductive enough to light up the LED in the cluster.  Cleaning the switch and boot and spraying with WD40 fixed the problem.

I agree with Daveyson that the problem is probably in the oil pickup or the oil filter gasket.  Wouldn't be a bad idea to pull the sump cover off and take a good look at the innards down there.

On the EME website under water/oil pump they have the sensors on special for $11, usually $13 and the rubber boot that fits over the connector is next to it for $10. The sensor comes with its own washer.

Was looking at those when you posted.. parts are on order, and probably wont get time to work on it till next week.

Don't be surprised if the old one is tough to get out. The torque spec for it is 40 Nm.

I put 10W40 in my K1100 for a bit and it would flicker at tickover in hot weather in France. A blip on the throttle got it to go out. But the cooling fan would also be running at this point.

A change to 20W50 mineral oil eliminated the flickering.

I now only ever use this, Motul 3000.

From my experience with older engines as wear progresses you will find exactly what you have. You didnt mention how hot is hot? If you are in 35-40c riding conditions as some do then its far more likely.

A check on fan to make sure cooling system is performing correctly is important.

As said though check out the oil pressure sensor first, I have had a few of these fail over the years.

I put 10W40 in my K1100 for a bit and it would flicker at tickover in hot weather in France. A blip on the throttle got it to go out. But the cooling fan would also be running at this point.

A change to 20W50 mineral oil eliminated the flickering.

I now only ever use this, Motul 3000.

From my experience with older engines as wear progresses you will find exactly what you have. You didnt mention how hot is hot? If you are in 35-40c riding conditions as some do then its far more likely.

A check on fan to make sure cooling system is performing correctly is important.

As said though check out the oil pressure sensor first, I have had a few of these fail over the years.

Thank you for the suggestions..

I am running 20W50 oil, and the oil light is flickering as I pull away in 1st gear after the bike is fully hot and when I am stopped at a traffic stop (after about 1/2 hour of riding).. Outside temps these day are around 80-90 degrees F.
If I roll to a stop and throttle up it does not come on.

I have heard the coolant fan come on in traffic, so that is functional.

I'm waiting on parts to be shipped and will replace the oil pressure sensor and rubber boot, oil, filter and drop/inspect/clean the oil pan this weekend or next week as I get time.

I got thu 1/2 of the job today..

Drained the oil, dropped the pan, replaced the oil filter, and replaced the oil pressure sensor.

I initially freaked out when I saw bits of material on the oil pickup screen, but it turned out to be slivers of old gasket material and not very much of it..  

The oil color looked reasonable for the age (1500 miles or so) and nothing unusual.

I am missing one oil pan bolt that I will need to replace,
and I now see that the oil sight glass is permanently stained at the middle mark, which means I may have had the oil less than what it should have been without knowing and thinking I was ok.

I will hopefully have time tomorrow to finish cleaning up the oil pan and gasket surface and lay a bead of permatex..  (my first time with a liquid gasket)..  sounds like I'll need to wait a day for everything to set before refilling the oil

Bonus, looks like a quick fix.

Could it be too low idle speed?

When you lay the bead of Permatex, don't be concerned about any that squeezes into the oil pan.  It will harden and you can remove the excess on the outside for a cleaner look.  I've had the excess bead sitting in the oil pan on next inspection and you have seen what the oil screen stops.

Everything is put together.. Still need to get some time for a longer ride to make sure all is good.

Looking back.. I think I now see the problem..

The oil sight glass is permanently stained at the 1/2 mark. I was most likely seeing that when I did my pre-ride oil check, and the oil level was probably low without me realizing, causing the oil pressure light to sometimes go on.

I now filled to the 3/4 mark and can see the fresh oil above the stain. Live and learn.

If you can see any oil in the sight glass with the bike sitting level then that is sufficient for proper lubrication; the oil pressure warning light should not light up or even flicker.

If you can see any oil in the sight glass with the bike sitting level then that is sufficient for proper lubrication

I did not know there was a stain blocking my view of anything below 1/2, so I dont really know how much oil I had before..
I checked prior to every ride and thought I was good.

Ernesto wrote:Looking back.. I think I now see the problem..
I was most likely seeing that when I did my pre-ride oil check, and the oil level was probably low without me realizing, causing the oil pressure light to sometimes go on.

Live and learn.

The oil pressure switch was the likely culprit. A switch can get clogged and not operate correctly, or its contacts can just plain fail from old age, causing a dim or flickering light. Regardless, the cause needs to be sorted quickly.  

One lesson learned from this situation could be that when there is an engine problem, without testing each procedure's results before doing another procedure, you really can't be certain of what you've learned.

My checklist for a flickering oil light. Hopefully this might help someone else.

1. A quick check under the bike for an oil drip
2. Oil level - a mechanical check with a dipstick, not a look at the sight glass because you could be misreading the level
3. The wire where it connects to the pressure switch. If it's corroded or split, I change it

Hmm. At this point could be the pressure switch, could be the indicator bulb.

4. If I have a spare pressure switch, change it because it's easier and quicker than dismantling the instrument housing
5. Dismantle the instrument housing and carefully check that the plastic PCB tabs have not got folded underneath the PCB and so are not making proper contact with the bulb housings. When you remove the bulb housing the PCB tabs are invariably pulled out with it and will very easily fold over rather than go back into the bulb slot
6. Check the wire contacts on the bulb. I have seen them broken off and only just touching the housing contacts
7. Change the bulb.

If it still doesn't behave correctly, run a wire directly from the one-way connector directly to pin 11 in the instrument housing (just strip the ends and poke them into the connectors). If it now works, you have a main loom problem. Check the wiring loom where it turns around the headstock because it has been known to start breaking up under repeated pulls against the fairing spider.