Oil Light ON after 15 minutes

[adidasguy]

OK. Here is a tricky one.
This involves the test motor we have at the Bike Cave.
True to what the PO said, the oil light comes on after 15-20 minutes of running. Wait a while and the process repeats. Oil is new, full and spotless.
You rev the engine and the light goes out. Back to idle and it blinks then stays on until you rev it up again.
Let it sit for half an hour and you can run again for 15 minutes or so before the oil light comes on.

What could it be? Is it time or temperature related? Could the oil pressure relief valve be opening up when it gets hot?

Here's the original story of this motor:

Bike was fine.
Cam chain guide shattered, filling motor with plastic bits.
Motor cleaned out.
Now the 20 minute problem started happening.
Oil pump replaced. Still same problem.
Oil sensor changed out.
Still same problem.
New oil, new oil filter
Same problem.
Always 15-20 minutes.
PO then gave up and swapped motors.
Motor sat for a year or two until a late night CL ad for a free motor if you just come take it away - which I gladly did.


Now we did remove the oil pan before setting it up to test. The oil pan was clean. No crud or plastic bits anywhere. Oil sump screen was clean. Initial thoughts were that crud collected on the oil sump screen and after 15 minutes, it was getting sucked to the oil sump screen filter and soon there was enough crud that it clogged up the oil intake. After sitting a while, the crud would fall back to the bottom of the oil pan until you ran another 15 minutes.

I was thinking it could be oil drain passages from the top end: oil getting stuck up there and no draining back down. But just as the oil light came on I checked the oil level and it was at full. 15 minutes later it was at the same level which means oil is not pooling up somewhere.

Suggestions?

[Big Rich]

Have you tried swapping the oil pressure sensor on the motor? I don't know the symptoms of a sensor that is "on its way out" - I've gotten good sensors and flat out bad sensors. But I would guess if it's heat related to the sensor, a known good one might be an easy fix.

[radodrill]

Is the oil pump itself working correctly?  Have you measured the actual oil pressure?

[Atesz792]

Sensor was replaced I think. Maybe when the cam chain guide shattered, it took some of the material in some of the oil passages, too? So the internal diamater would increase, and so resistance against oil flow would decrease. 15 minutes pass by, oil gets thinner to the point it no longer produces enough pressure with the decreased resistance. Supposing that the new oil pump is spotless.
If this is the case (which would be a tough diagnosis if you want to make absolutely sure...) I think some thicker oil might be your simplest solution.

[adidasguy]

The PO said he changed the sensor.
Only way to know would be to get a real oil pressure meter and see what the pressure really is.

No need for different oil. We are using the same AmsOil we use in all our bikes. We want to find the cause and fix it, not do something to mask the real problem.

Worst case we part out the motor. Rather fix it and have a good, free motor for our next project. (Two more builds on the schedule)

[Atesz792]

Just saying... pressure differential required for certain flow (and vice-versa) relates to the 4th power of the diameter in which you pump the fluid. That makes a slight increase in diameter cause a huge decrease in oil pressure. Not trying to be a smartass here, but English is not my first language, so.. yeah. You could have that, or a bearing going out for example, I think that can have a similar effect. Of course you wouldn't want to just mask the latter, that's why I said it's a tough diagnosis if you want to be absolutely sure.

[Old Mechanic]

Get a gauge on it, compare it to a known good engine. Sounds like excess clearances.

regards
Mech

[adidasguy]

Altesz: I understand what you're saying. We don't want to use thicker oil to solve the problem. We want the motor running correct with the right oil. With so many GS500's here, it is not wise to have one motor that requires special oil.

It is possible some passages were cleaned out too much by the previous owner or some were drilled through to the wrong place.
I do not believe the PO drilled out passages. He just cleaned things out.

First is buying an oil pressure gauge. Then we will know more.
It could be the oil pressure relief valve or maybe o-rings are missing on the oil pump - those are my first 2 guesses. If temperature on the oil sensor, we can spray some cold spray on it when it comes on and see if that changes things.

[bmf]

I agree with the oil pressure gauge test.

When the light comes on the pressure is really low.

Also do you have the right sump gasket, new type gasket in old type engine has a huge space where the oil leaks through - ask me how I know.........

Brett

[robfriedenberger]

Also a temp gauge should be used as well


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[Blueknyt]

adidasguy.... pop off the clutch side cover after you do the oil pres gauge bit, grab the counter bal shaft and see if there is any play up and down or front to back in relation to the engine (not left to right inline with its bore)  ive got an engine on the bench right now, that had the same thing happen and found it wiped the bearings on the CB shaft but the Crank main and rod bearings were fine.  i have a feeling the CB shaft gets shitty oiling to begin with, in fact the line for the CB shaft comes off the main galley, to the pressure switch, through an orifice to CB bearings.

[adidasguy]

Engine is I think 07. We replaced sump gasket because we opened it up to have a look see. Correct gasket for sump with oil cooler.
We'll do some tests this weekend and see what develops.

Suggestions for oil pressure gauge for $50 or so?

[robfriedenberger]

Cheap-o harbor freight ones work fine