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Oil Pressure light on 87 K75

48882

48882

Member
I had previously posted about my oil pressure light here: https://forums.bmwmoa.org/threads/1987-k75t-broken-wire-to-oil-pressure-switch.108914/

The light is coming on, but I don't think it is related to the wire. The light come on and stays on after the bike has been running for a while. If there was an issue with the wire, it would either not turn off or turn of and on during the ride.

I have read another post where it was suggested that the oil filter might not be tight. I have changed the oil/filter since this started happening and the old filter was on tight and the new one was installed properly (I believe)

A couple of thousand miles ago, the water/oil pump was rebuilt, but I drove 2k+ miles without the light coming on. So I believe the rebuild was done correctly.

I have driven the bike 1k+ miles since this has started happening, and I see no ill effects so far. Bike has 125k on it.

Any thoughts on what else it could be?
 
First, I’d recommend hooking on an oil pressure gauge and verifying that your pressure is ok. If the pressure checks out ok then I’d recommend installing a new oil pressure sending unit. They’re not overly spendy.

Best,
DeVern
 
Paul Glaves's response is very interesting and intuitive.

Yesturday, riding back from an advanced moto course, I noticed a dim red low oil pressure light trying to glow after riding in what was probably the worst pouring rain storm I have every ridden through in my riding days since 1977. The light became progressively brighter as I kept on driving to make it home. I did check the oil level in the crankcase and it is exactly where I put it after the major clutch overhaul last January.

I did a login this morning to report my situation and the first post I see is about an Oil Pressure Light on a 87 K75, the only difference being mine is a 93.

DeVern is right, the pressure switch is only $10 from EME and I was getting ready to order one. The shipping costs though are terrible.

Definitely going to check that boot, which is also $10 from EME.
 
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Will remove the belly pan and inspect the pressure switch this morning. If I remove the pressure switch, will engine oil leak out due to location of switch below oil level line?
 
TEST the switch and the wiring and the bulb first.

Disconnect the wire from the oil pressure sender. Take a jumper wire (preferably with alligator clips on each end. Clip clip to end of oil pressure wire and the other end to the ground wire just above the shift lever. Turn on key and the kill switch. Does the light come on? Yes, the wiring is good and bulb is good. No, wiring or bulb is bad.

Take an ohm meter and measure from oil sender to ground above shift lever. Key and kill switch on. Start engine.
Complete circuit Yes, sender is good. No, sender is bad. <I Believe this is backwards!!!

1.WITH THE ENGINE RUNNING (with oil pressure) the sender should show an OPEN CIRCUIT to ground (no light).
2.WITH THE ENGINE RUNNING (with oil pressure) the sender is bad if it shows a CLOSED CIRCUIT to ground (light on).

3.With the engine off (no oil pressure) the sender should show a CLOSED CIRCUIT to ground (light on).

If #1. Is bad you either have extremely low oil pressure or the sending unit is bad. Let’s hope it’s the latter.




:dance :dance :dance
 
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Just to close the loop on this issue, the bike sat for two days on my lift. When I got to it, I checked the rubber boot and it was dry.

Followed 98lee's advice and the test revealed a functional pressure switch.

I guess Paul Glaves was bang on wrt water seeping into the rubber boot. The issue happened while returning home riding in heavy rain (yeah, I know). At first the low oil pressure light bulb was faintly glowing. I had the low fuel light brightly lit and so there was a good comparison staring me right in the face. I should have checked the rubber boot when I got out of the rain but meant removing the belly pan and I was too tired and nursing a bad shoulder.
 
Recheck your sender. I got the instructions backwards. Recheck my previous post. Crazy day!



:dance:dance:dance
 
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GasStation said:
Just to close the loop on this issue, the bike sat for two days on my lift. When I got to it, I checked the rubber boot and it was dry.

Followed 98lee's advice and the test revealed a functional pressure switch.

I guess Paul Glaves was bang on wrt water seeping into the rubber boot. The issue happened while returning home riding in heavy rain (yeah, I know). At first the low oil pressure light bulb was faintly glowing. I had the low fuel light brightly lit and so there was a good comparison staring me right in the face. I should have checked the rubber boot when I got out of the rain but meant removing the belly pan and I was too tired and nursing a bad shoulder.
Click to expand...
That sending unit grounds the connected wire (lighting the bulb) when oil pressure is absent or low. The wire connector is bare and water in the little boot provides a path to ground to the engine case even when there is oil pressure. Thus the light can flicker or come on when water in the boot provides a path to ground. I discovered this while riding across Oklahoma on a trip from Kansas to a Houston Club rally. When the light came on I stopped and while trouble shooting found the little rubber boot had water in it. After dumping the water and splashing a bit of IsoHeet in the boot and around the connection the light stayed off so I proceeded on to Texas and then later back home to Kansas.
 
Yep, my exact experience and initially I was somewhat concerned that I was "running low on engine oil pressure".

Yesturday, with the bike on the lift, I thought of securing the rubber cap with an additional tiny T-wrap over the small lip there is on the pressure switch assembly. Then, I thought that this a ONE TIME occurrence and I've had this bike for well over 20 years and after 47,000 kms, that was the only event.

So, I cracked open a beer and listened to "Riders on the Storm - Doors" as a tribute. 🍺
 
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