False (Hopefully) Oil Light - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 7 (permalink) Old 05-14-2019, 01:46 PM Thread Starter
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False (Hopefully) Oil Light

Twice now, I've started the bike cold in ~45F weather, and I've seen the oil light on when it starts up. I shut the engine off and restart, and the light goes off as usual.

The oil level is fine, and the level drops (as expected) when running. The light has never come on while riding or idling, hot or cold. Only immediately after a cold start. Beyond the light itself, I've never had any indication that there's a problem with the oil. Has anyone ever experienced this? I'm suspecting the pressure sensor itself.

I don't know if it's related but, I've also had some intermittent electrical issues in the ignition. Sometimes I have to jiggle the key to get everything to turn on, but it's never shut off on me while running. Today, after stopping for gas, I somehow got it to start and run with the Tach reading 0. My idle is ~1000. I turned the key off and back on, and restarted and the Tach functioned normally. This may or may not be related to the oil light issue.

I'll probably need a new ignition soon.


'89 Vulcan 750 Bought 4/12/18 @ 17805.9 miles $800
Purchased stock. Wrecked once
26980.4+ miles

Completed modifications:
Removed mufflers, straight pipes out of GB
110/90 Front Tire
Pick-up coil re-gapped to .020"
Compufire 55402 r/r series regulator
USB Outlet + Voltmeter
Repainted Metallic Blue w/ new tank bages
Ear Shave (wo/ coasters) 40/140 NO shims 45MPG
MCCT conversion

Planned modifications:
Custom LED turn signals
Windshield
Highway Pegs
(Possible) ignition advance
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post #2 of 7 (permalink) Old 05-14-2019, 05:22 PM
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I’m not a mechanic, I’ve read plenty of folks on here with a hell of a lot more experience than I but my first guess would be to check the electrical connections for those circuits. Corrosion can short or open circuit. Also temp can play into any electro-mechanical issues due to expansion and contraction etc. Just a thought
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post #3 of 7 (permalink) Old 05-14-2019, 10:01 PM
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I take oil lights seriously. check the connection at the pressure sensor. Remove the sensor and take a look at it. I have seen oil pressure sending units fail or partially fail from sludge buildup.

I am a motorcyclist, NOT a biker.


1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike
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post #4 of 7 (permalink) Old 05-15-2019, 03:14 AM
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It's likely a bad pressure sensor.

For what it's worth, the ignition switch can't drop the tachometer without also dropping the starter circuit.
If your bike is already running and the tach drops to zero, you're in a scenario where your 'voltage monitor' wire going into a non-mosfet R/R may be zero, and your R/R may burn up trying to bump the volts higher, or may pass a much-higher-than-wanted voltage to the rest of your electrical system.

1992 US-nonCA * tuxedo mod * r/r relocated

Vulcan slang for newcomers
Service Manual Download
Wiring Diagram + annotations * still undergoing revisions, but still more useful than the generic one. Let me know if you find mistakes or think something additional should be added
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post #5 of 7 (permalink) Old 05-15-2019, 06:32 AM Thread Starter
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I have an aftermarket R/R without a monitor wire connection. It only has three stator connections, battery and ground. The tach thing was really weird!

I'll keep an eye on the oil light. I have an external oil pressure gauge. Does anyone know what the pressure is supposed to be? I may be able to connect the gauge and verify the actual pressure.

I had a pressure switch fail once on a Mercury Sable with 220,000 miles. It was enough miles that it could have legitimately had no oil pressure, but the external guage showed right at factory spec. My old F150 on the otherhand, showed actual low pressure and it got a new V8 a couple of years ago. I'm hoping for the Sable situation and not the F150 situation.


'89 Vulcan 750 Bought 4/12/18 @ 17805.9 miles $800
Purchased stock. Wrecked once
26980.4+ miles

Completed modifications:
Removed mufflers, straight pipes out of GB
110/90 Front Tire
Pick-up coil re-gapped to .020"
Compufire 55402 r/r series regulator
USB Outlet + Voltmeter
Repainted Metallic Blue w/ new tank bages
Ear Shave (wo/ coasters) 40/140 NO shims 45MPG
MCCT conversion

Planned modifications:
Custom LED turn signals
Windshield
Highway Pegs
(Possible) ignition advance
Jason Pittenger is offline  
post #6 of 7 (permalink) Old 05-15-2019, 11:07 AM
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At 1,000 RPM, the oil pressure should be 2 to 4 lbs. At 2,000 RPM the oil pressure should be 30 to 38 lbs.

I am a motorcyclist, NOT a biker.


1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike
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post #7 of 7 (permalink) Old 05-15-2019, 12:03 PM
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What??? At idle, the oil pressure should be -at least- 15-20 psi.

1986 VN750 27k miles
1999 EN500 32k
1983 GL650i in pieces. Someday it will ride again.
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