Oil light comes on at low rpm

@slmjim+Z1BEBE

Yea I'm gonna ride around for a bit so I can get a more accurate reading. The oil temp is listed in the pressure table I attached to one of my replies: 90C (194F)

Went for a 30 minute ride, which was long enough to get the oil light on - this time it only stayed on below about 1300rpm.

I checked the oil pressure at idle, and the needle looked like it didn't really move at all. When revved to 4000rpm, I got the reading pictured below. Looks like about 15psi, which falls beneath the 28-36psi range listed in the FSM. Does this mean there could be a problem with the oil pump, since the relief valve appears to be operational? 

We're always reluctant to contribute to threads on bikes we're not familiar with, such as  KZ550's.  That being said:
The pressure spec leads us to believe KZ550A motors are a plain bearing design that rely on pressure instead of volume, as in the big block roller crank motors.

Did you change the filter when changing the oil?  Some pressure drop across the filter is normal, but what you're seeing isn't.  I appears that the filter on a KZ550A is a cartridge filter.  Perhaps defective?  We'd try either replacing the filter with an OEM filter or, try a quick & dirty test by removing the filter, then replacing the filter cover leaving the filter cavity empty and testing hot pressure again.  No filter will eliminate the filter as a possible culprit.

How many miles on the motor?  Bearing wear will reduce oil pressure.

We noticed a compression gauge is used for oil pressure testing.  Is it rated for that?  We've never tried that and have to question the accuracy of the result.  Too, the result is very, very close the bottom of the scale where mechanical pressure gauges in general are not accurate at all.

Good Ridin'
slmjim & Z1BEBE

To answer your question, the odometer is at 31,500 miles.

I too was skeptical about using a compression gauge to test oil pressure, but the guys at Advance Auto told me it would work.

I did replace the filter, so it could be worth performing the test you mentioned. Is it risky to run the motor without the oil filter in place? I'd have to ride like that for 15 minutes or so to get it fully warmed up. 

At 31K  mi., there may well be bearing wear affecting oil pressure.  Running 20w-50 might increase hot pressure enough to reduce the tendency for the oil light to energize at idle.  Only way to check bearing wear would be a complete teardown and mic and/or plastigauge test of all bearings & journals.

As far as testing oil pressure sans filter, we'd try this:
Prepare all the tools needed, catch pan, rags and workspace in advance.  Ride the bike for 20 ~ 30 miles to get everything to operating temp.  Immediately upon returning to the workspace, drain the filter cavity, remove the filter & reassemble as quickly as possible.  The motor & oil should still be hot enough to get an accurate hot pressure reading.  Oil light still on?  Pressure reading change?

But...

Even though the needle moves a tiny increment on the compression gauge when testing idling oil pressure, it's still the wrong tool, operating at the extreme 3% ~ 5% bottom end of a scale that doesn't have enough resolution for an accurate reading to begin with.  So, as far as the guys at Advance Auto, yeah, they're right; it does 'work'.  The needle moves.  It just isn't designed for pressure as low as what you're dealing with.

Good Ridin'
slmjim & Z1BEBE

wrote:

Even though the needle moves a tiny increment on the compression gauge when testing idling oil pressure, it's still the wrong tool, operating at the extreme 3% ~ 5% bottom end of a scale that doesn't have enough resolution for an accurate reading to begin with.

 

Yeah, I agree with this.   It looks like there are several 0-100 psi gauges on Amazon.  That range would more closely match the expected range for your bike (28 to 85 psi).

Something like this?   www.amazon.com/OTC-Tools-5610-Trans-Eng-Tester/dp/B000R5G0DO/

Rather than buying another pressure gauge and running the bike without the filter to perform this test, I think I will simply replace the filter since it's only about $12 and see if that stops the oil light from coming on. If that fails, then I will revisit your other suggestions, as they seem more expensive and time-consuming. I'll post an update when I have more news to share.

Quick question: am I able to change the filter without draining the oil? I just changed it 1200 miles ago, so I don't really want to do that again just yet if it's not necessary.

Might be saving money on the front end but losing a bucket full on the back end if the engine grenades lack of oil pressure. Might want to rethink this. 

@Mikaw

I'm not sure I understand your concern - what's the harm in replacing the filter, taking the bike for a 15 minute ride, and seeing if the oil light comes on? I would need to ride it for that long anyway in order to warm it up enough to test hot pressure, so why not try the cheap and easy fix first? 

Oil light is a warning. you have to assume there's an oil pressure problem & the engine is in danger of severe damage.  it very well may be a glitchy switch, especially on models with the switch located at the oil pan where crud can more easily gum up the switch, but you have to assume the worst.

wrote:

@Mikaw

I'm not sure I understand your concern - what's the harm in replacing the filter, taking the bike for a 15 minute ride, and seeing if the oil light comes on? I would need to ride it for that long anyway in order to warm it up enough to test hot pressure, so why not try the cheap and easy fix first? 

Diagnosis in my opinion is the cheapest insurance. If your driving a plain bearing engine without the oil pressure needed to float the item, ie. Cam, crankshaft, your rolling the dice every time you head out. I’m just saying I would find out why you have an indicator light coming on. It might be the sensor, but it might be a serious issues. If the latter then catching it while you still have intact parts to rebuild, you farther ahead. God forbid you wipe out a crankshaft or cam, even worse toss a rod out of the case. A little diagnoses using the the least destructive process in my opinion is best. Remember you not trying to figure out why a $3 light bulb is blowing. Your dealing with expenses internal engine parts. 

Edit: Years ago I had a 1978 Ford LTD that my girl drove daily. She called me one day during work and said the car overheated and broke down. Come to find out it tossed a couple rod bearings and seized up. I asked my girl” did you notice anything different”, she said, “come to think about there was this little red light that came on about 2 weeks ago” 

 
You make good points, and I understand that it is a smart idea to err on the side of caution. But don't these pressure tests still require me to ride the bike to get it to operating temp? 

Also, do you agree with @slmjim+Z1BEBE that I should test hot pressure without the filter in place to eliminate the filter as a possible culprit?