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Oil pressure light always on

Discussion in 'The Garage' started by buztabuzt, Jun 14, 2019.

  1. I'm trying to decide whether my oil pressure light being on is an actual pump failure or something else like a faulty sensor or light. Needless to say I'm thankful I haven't seized the engine already and I'm going to avoid running it until I have it figured out.

    I have seen at least one other thread where it was a pump failure. I'm going to continue doing some searching but curious if anyone knows a good test for the pressure sensor. I had recently changed the sheaths on the wiring from the oil sensor under the sprocket but don't think that would have affected anything.

    On the one hand the pump would make sense and not be the end of the world to have to replace. it would alarmingly justify the smoking header pipes and spark plugs getting very hot in short time (perhaps that's normal?). I unscrewed the front right (exhaust?) valve cover and while there was dampness in there I didn't see any oil flinging out.

    On the other hand, the oil level does go down in the site glass upon turning over and goes further down under revs, almost out of sight. With re mentioning that my oil filter was missing a washer between filter and spring which I'll replace next change - wouldn't think that would drastically changed oil pressure

    Any tests or suggested next steps would be thoroughly appreciated!
     
    Last edited: Jun 14, 2019
  2. XSLeo

    XSLeo XS400 Junkie

    On cars we used to pull the pressure sending unit and install a fitting and hook up a regular pressure gauge. Start the engine and look at the pressure on the gauge. If ok the it was the sending unit.
    If not ok you checked further,
    Leo
     
  3. xschris

    xschris a lifestyle not a trend Top Contributor

    Have you checked the sump screen? Another thing to look at it the oil galley before the sensor. It's behind the bolt on the left side of the motor next to the sensor. This is where the most pressure is for the main crank bearings. Make sure it's clean in there and then prime it by pumping oil through the hole that the oil filter bolt goes in. I have had a sensor stick on one of the bikes I bought that had sat for a number of years. A gentle tap freed it up. These motors run 60+psi of oil pressure so if you do put a gauge on it I would look for those type of numbers.
     
  4. I had cleaned sump screen, found a non-metallic flake in it but nothing i would consider as clogged:
    http://www.xs400.com/attachments/img_20190411_170706-jpg.33437/
    Can't recall that I had a good look up into the sump/guts though...

    Buddy found this oil sensor test procedure in a honda common service manual that seems a good test for a ground... otherwise I'm thinking pump.

    Oil Pressure Switch.jpg


    Is oil galley circled in pic? Procedures would be redrain oil, make sure it's clean, make sure sensor is clean and give a gentle tap, pour some oil into the oil filter bolt hole, and pray to the bike gods?
    Thanks lads! I don't have an oil pressure tester. Not opposed to buying one, but finding one to fit and wasting 3 more rounds of oil (if attached down low) would be my hesitation.

    IMG_20190614_115459.jpg
     
  5. xschris

    xschris a lifestyle not a trend Top Contributor

    Yes that bolt in your pic. If you open that up only a little oil will come out. If you remove the oil filter only what's in the housing will come out no need to drain the entire bike to check this.
     
    buztabuzt likes this.
  6. Brilliant. Shall be next on my list. If I remove the sensor would that dump all the oil? Not the end of world but figure I can try to clean and test it as well. But I'll first test everything that doesn't require full oil change
     
  7. Haynes manual states oil pressure light goes on up to about 1500 RPM. Can anyone attest to this? Does your light stay on at low idle or go out immediately after it cranks over in low idle?
     
  8. xschris

    xschris a lifestyle not a trend Top Contributor

    Mine all go off a soon as the motor turns over a few revolutions. Even if I kick it once.
     
    buztabuzt likes this.
  9. Thanks Chris. You know if removing sensor means opening oil flood gate? I presume so...
     
  10. xschris

    xschris a lifestyle not a trend Top Contributor

    no just what's in the crank bearing oil feed galley. Maybe 4-6 fl oz. Same as removing that bolt next to it.
     
    buztabuzt likes this.
  11. Got the oil galley opened which only drained 2 oz. Oil generally clean with some small sediment at bottom.

    Having no success removing oil pressure sensor with any wrench, channel locks, sliding wrench, etc. Pain in butt. Looks about 27mm. I don't have socket that big and 1 slide wrench too small other so big it doesn't have room to turn. Any suggestions to remove it? I know it says don't overtighten in manual but not how to remove!
     

    Attached Files:

    Last edited: Jun 23, 2019
  12. xschris

    xschris a lifestyle not a trend Top Contributor

    I have only pulled one off in the past and I think I used large channel lock to do it. It's been like ten years so not sure what else I could have used. Looks to be a fair amount of carbon in there.
     
  13. Got her out with some pb blaster penetrating lube. nothing on sensor that looks like an obvious fault. I think my next logical move is 2 introduce myself to the oil pump. My next step will be trying to figure out how to test it with manual and YouTube.
     

    Attached Files:

    Last edited: Jun 27, 2019
  14. Gra900

    Gra900 XS400 Member

    The most likely cause is a faulty pressure switc. It’s also easiest to check with a new one. Or Even better, get a pressure gauge and screw it in to check what pressure you really have.
     
  15. Thanks all for the input. After nothing obvious on the switch I took a month away for work, travel, family, and to ride my functioning bike! Well, a fresh set of eyes worked wonders. The blue neutral switch wire was hooked into the oil sensor (so neutral light would illuminate with low oil pressure, and oil illuminated because it was in bloody neutral the whole time)!

    Resorting my wires and going to try to test it out again this weekend or next week.

    The result as always: never trust a prior owner :)
     

    Attached Files:

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