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  1. #1
    Veteran Member
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    Jun 2003
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    East Texas, USA
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    Kubota Grand L4740, B2400 and F2680

    Default Low Oil Pressure

    I went over to the farm this past Sunday to do some mowing. I took out the 1979 MF 275 because it hadn't been used much lately since we got the new kubota. I checked it over and greased it before I took it out. The oil was a little below the full mark but not too bad, probably less than a pint. The oil pressure gauge was running a little lower than I remember it (it used to run in the middle of the green) but it was still just in the green at PTO speed (1700 rpm) and went back towards the middle of the green when at idle. I made a mental note to top up the oil before using it again. Well, I was over at the farm again today and My S-I-L was off on the Kubota so I took out the old MF 275. I topped up the oil to full and this time the oil pressure was on the green/low borderline at idle and dropped into the yellow when at PTO speed.

    The oil and filter were both changed last year and probably have less than 30 hours on them but the tractor has been sitting around for about 5 months. The oil still looks relatively clean on the dipstick.

    I don't want to ruin the engine by continuing to run it so I'm looking for guidance as to the possible cause of the low pressure reading or things to try before I start ripping it apart or hauling it off the be fixed. [img]/forums/images/graemlins/confused.gif[/img] [img]/forums/images/graemlins/confused.gif[/img] [img]/forums/images/graemlins/confused.gif[/img]

    Any help or suggestions would be greatly appreciated. Thanks in advance.

  2. #2
    Elite Member SnowRidge's Avatar
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    Jul 2003
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    3,091
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    East Tennessee
    Tractor
    Power Trac PT-425 / Branson 3520

    Default Re: Low Oil Pressure

    If I read your post correctly, the oil pressure drops as the RPMs increase. Is that correct? Has it always been that way? I would expect the oil pressure to increase as the engine speed increases until the relief valve opens, at which point it should hold steady.

    Is the gauge mechanical or electrical? It almost seems like an electrical problem. [img]/forums/images/graemlins/confused.gif[/img]

  3. #3

    Default Re: Low Oil Pressure

    just a thought, any chance of water getting in the crankcase? oil sits on water so when you check dipstick you would only see oil, when oil and water mix it looks kinda like a milkshake, i would change the oil and filter, you never know if oil has sludged up and there is a restriction in the filter(although sometimes that will cause extra pressure). also, pull the wire off the oil sending unit and ground it, oil pressure should slowly climb to max-that'll tell you if gauge is working, if it is and oil change doesn't change anything, replace the sending unit. good luck!!!!

  4. #4
    Epic Contributor Soundguy's Avatar
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    Central florida
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    ym1700, NH7610S, Ford 8N, 2N, NAA, 660, 850 x2, 541, 950, 951, 2000, 3000, 4000, 4600, 5000, 740, IH 'C' 'H', CUB, John Deere 'B', allis 'G', case VAC

    Default Re: Low Oil Pressure

    Another idea is fuel contamination in the oil thinning it.. making for the lower pressure.

    Soundguy

  5. #5
    Veteran Member
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    East Texas, USA
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    Kubota Grand L4740, B2400 and F2680

    Default Re: Low Oil Pressure

    </font><font color="blue" class="small">( <font color="blue"> the oil pressure drops as the RPMs increase? </font> )</font>

    Yes it does and that's one of the things that puzzle me. I would have expected the opposite. The needle on the gauge has always run dead center of the green section, right in the middle of the gauge.

    I think the gauge is electrical but I brought the manual home last night so I'll check to make sure.

    I'll be going back over to the farm later today or tomorrow so I think I'll pick up a filter and oil and change them although I can't see how water could get in unless there is something very serious wrong. I'll also check for any bare wire problems.

    Thanks for the ideas.

  6. #6
    Platinum Member
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    Sep 2004
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    south/central Va.
    Tractor
    Deutz Fahr Agrofarm 100, Stoll loader, bucket, forks & root grapple

    Default Re: Low Oil Pressure

    I hope the problem is the gauge. I had a 574 IH that did the same. It was the oil pump. I fed cows with that tractor so it was used every day. I noticed the pressure change and it worsened fast. Each day it was a little lower. Put in a new pump and the problem was solved. The screen over the pump can get clogged and show the same symptoms.

  7. #7
    Veteran Member
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    East Texas, USA
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    Kubota Grand L4740, B2400 and F2680

    Default Re: Low Oil Pressure

    I changed the oil and filter on Sunday. It helped a little. At least now it runs in the green, but only just, and drops to the borderline between the the green and yellow when raised to PTO speed. That may be the result of using 15W-40 oil instead of the straight 30 weight. I also checked for any bare wires but didn't find any. Overall, the pressure is still running lower than it used to run. I think it's time to move on to the next step and check out the sender unit, if I can find it and make sure the filter on the pump isn't clogged for some reason. After that I guess it's gauge time and check out the oil pump.

    It sure would make things a lot easier if I had a workshop manual for that thing. May have to see if I can track one down.

  8. #8
    Epic Contributor Soundguy's Avatar
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    Central florida
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    ym1700, NH7610S, Ford 8N, 2N, NAA, 660, 850 x2, 541, 950, 951, 2000, 3000, 4000, 4600, 5000, 740, IH 'C' 'H', CUB, John Deere 'B', allis 'G', case VAC

    Default Re: Low Oil Pressure

    If it is in the green at idle.. but drops at throttle.. I'd sure check out something. Most worn oil pumps.. or loose bearing clearances tend to have low pressure at idle.. that gets a little better at throttle.

    Soundguy

  9. #9
    Bronze Member hbarski's Avatar
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    Apr 2005
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    Tenn/Arkansas
    Tractor
    3930 Ford/Newholland Mitsubishi MT2001D CASE 580 CK

    Default Re: Low Oil Pressure

    basic wrench turning 101 says, when shotgunning parts, prioritize most likely culprits, and replace easiest/cheapest first. If its electric driven single wire, check your grounding at gauge and engine first. Check wire run to gauge second. Price gauge and sending unit. Replace cheapest. My guess is grounding (first) or sending unit.

  10. #10
    Elite Member
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    Mar 2002
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    3,310

    Default Re: Low Oil Pressure

    Sending units are cheap, (usually under $10). I would jump on that immediately.

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