Topic: Oil Pressure Conundrum

[The Lone Builder]

I took the bike for a ride yesterday and the oil pressure light stayed on until I revved up to about 2000rpm. It cam on again when the revs dropped. Last time out, all was fine.

The it came on and stayed on. I checked oil in the tank and while it was a bit low, it was still half way up the stick. I rode home - now a total of 5kms with no apparent ill effects.

Today I checked the pressure with a gauge. When I removed the galley plug, no oil came out, though now there is a bit of a leak, so oil is getting there. The pressure was up to 60psi almost instantly, but the light was still on. I recently changed the oil pressure switch and it was working fine previously.

However, not being happy, I checked what was happening at the rockers; there was no oil splashing out and they seemed dry to me.

My next step is to check, for change the pressure switch, but it is the dry rockers that are worrying me. I only checked No 4 cylinder, so I'll also check the other side.

Any thoughts or suggestions would be most welcome.

[newday777]

Did you check exhaust side or intake side? Check 1 and 4 exhaust side.
What oil?
Has this bike just been woken up from a long sleep? What's it's history??

[denward17]

Did you check the rockers with it running, or just turning over the starter?

[MauiK3]

I know it’s a pain but maybe pull the pan and look at the screen.

[Tracksnblades1]

LB,
For a starting point, the service manual indicates the 750’s oil pump relief valve spring it set for
 “56.9 psig @ 4,000 rpm with the oil temperature at 176*f…

You could verify it has oil pressure with a known mechanical gauge.
Then test your oil light pressure switch. It’s activation pressure is in the manual also and is quite low..

[Tracksnblades1]

It reads the oil pressure light goes out when ever the oil pressure is above 7.1 psig..

Edit: And operation with oil temps at 244*f or higher can cause intermittent oil light activations during idling @ 800-900rpms.
        as well as discouraging operations with an illuminated oil light..

[The Lone Builder]

The mystery deepens.

Why is my oil warning lit staying lit?

I inspected the oil gallery and all the holes seemed to be clear.
I checked the pressure switch with an air hose and it was working as expected, so I put it back.
At this point the gauge was reading 60psi as soon as I started the engine, and remained there up to 4000 rpm.
Oil light still remained lit, so I checked the wiring - just to be sure. When the blue/red connection in the headlight was broken, the light went out, so no additional feed to the switch.
I was still not getting the splashing oil at 1 & 4 exhaust tappets that I was looking for.

I replaced the switch; no change
I removed the gauge.
With the bike on the side stand, there was a bucket of oil coming out the No 1 exhaust valve.
With it back on the main stand, oil appeared at the No 4 valve also.

So, great news, yes? Problem solved!
NO!! the light still remains lit!

So does anyone have any ideas as to why the light should remain lit when measured pressure is good, and observed supply to the top end is also good?

Please, any ideas welcome.

[newday777]

Did you inspect the wire for fraying? Any bare exposed wire can be the ground that the pressure switch is designed to do to make the light emit.

[Tracksnblades1]

If both oil pressure switches have no constant continuity to ground above their activation set point, you’ll have to find where that wire is being constantly grounded.

[ekpent]

Wish I could solve your problem for you. Oil light on regardless of the cause is unsettling. I'll pass my story along incase someone someday has my issue. On a K4 I have the oil light was bright and nice with engine off and went off when started.  When in gear it would be out but in neutral it would come back on but not as bright. It worried me for a bit until I looked at the dash lights and found a hole had burned through the plastic housing holding the bulbs and light from the neutral light was bleeding in next door to the oil light. Little dab of black silicone in the hole and my oil light problem was fixed. Easy fix on that one.

[The Lone Builder]

I had that problem too, until I changed the oil switch. Now it glows like the midday sun, so there is no doubt about when it is lit.

  Joy to the world!

Having been pointed towards the right diagnosis, I have now resolved the problem.


As suggested above the blue/red wire was permanently grounded, behind the final drive sprocket, just before it enters the starter motor housing.

In retrospect my thinking should have been:
Light is on:
Pressure is good, given the pressure gauge reading (60psi)
Check the switch. Even though the switch appears to be OK, there is no change even with a new switch so it is unlikely that the switch is the problem.
Only thing remaining is the wiring .....

Probably would have saved me several frustrating hours of nonsense.

Thanks for your thoughts.

[willbird]

I had that problem too, until I changed the oil switch. Now it glows like the midday sun, so there is no doubt about when it is lit.

  Joy to the world!

Having been pointed towards the right diagnosis, I have now resolved the problem.


As suggested above the blue/red wire was permanently grounded, behind the final drive sprocket, just before it enters the starter motor housing.

In retrospect my thinking should have been:
Light is on:
Pressure is good, given the pressure gauge reading (60psi)
Check the switch. Even though the switch appears to be OK, there is no change even with a new switch so it is unlikely that the switch is the problem.
Only thing remaining is the wiring .....

Probably would have saved me several frustrating hours of nonsense.

Thanks for your thoughts.

I work in Industrial Maintenance, on the PLC controls side now. IMHO the best trouble shooting methods involve working through the circuit from one end to the other. I typically start at the end that often has the most failures in the past. One issue that comes from part swapping is swapping in a BAD part and leaving it in place. He have a compressed air heater on some machines. More or less it is a 1200 watt heater that 10PSI of air is pushed through so the air comes out hot. It has a 4 prong plug. Two wires are an RTD to sense temperature, the other two prongs are the 1200W heater. This was a production breakdown call, I had grabbed a new heater from stock and was taking it out while explaining to a new guy how to test the heater with an OHM meter and I noticed that the heater was an open circuit. Since then I have always tested a new part in every way that I can. I even test "new" fuses now. Takes only a few seconds and can save you from tearing a lot of your hair out.

Working through the problem as you did logically IMHO is the correct way.

You isolated the possible problems down to a short to ground somewhere in the circuit, then found that :-). Nice work :-).

[The Lone Builder]

I wish I could take the credit; it was Tracks and Newday who pointed me in the right direction.

I started where I believed the most common fault to occur; the switch. I tested it and my error was in not believing the result of my test and moving on to the next step.

Did you inspect the wire for fraying? Any bare exposed wire can be the ground that the pressure switch is designed to do to make the light emit.

Maybe I've misunderstood what you meant by this, but just for clarity.
The switch body is grounded and the internal switch breaks the connection between this and the live feed when oil pressure is sufficient. But it was indeed a bare wire grounding that was the issue; even when the switch broke the connection, the fact that the live was still grounded meant the light stayed lit.

[newday777]

Glad you found it. It's a fairly common problem of the wire getting chafed completing the ground circuit instead of the pressure switch.

[Tracksnblades1]

Good work TLB.

Just to share a toilet stall quote at a Catholic Hospital near the biomedical department.” And the Lord proclaimed E=IR and then there was light”. 😇

[PeWe]

When down there, check that alternator, field coil wires are properly connected.
Ensure that bullet plugs sit hard together and fully seated.
Contact spray can be a good idea.