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  1. #1

    Default Low oil pressure & dropping with higher rpms on Lehman 120 hp twins (?)

    I'm a prospective buyer of a GB with twin 120 hp Ford Lehman 2714E diesels, 1974 vintage, about 3,000 hours. Baffled by the mechanics' oil pressure readings and eager for insights. New 30-wt oil in both engines (replaced 10-40). In neutral, at idle, cold start to 1500 rpms shows 25 psi. Revving up to 2000 rpms the oil pressure drops to 20 psi and stays. Readings are from independent gauges directly on the engine blocks. Temp shows 150 degrees. They stay at 20 psi until engine rpms are brought down to idle at 750 rpms. Same story for both engines. Mechanics say oil pressure should be 30 up to 40 psi. What could cause that? Engines sound ok; exhaust is pretty clear; oil analysis is pending.

  2. #2
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    6,881

    Default Re: Low oil pressure & dropping with higher rpms on Lehman 120 hp twins (?)

    hard to say without any maintenance history....the oil analysis should give you better insight.

    If the oil used was too thin (over the years) the engines could have suffered excessive wear and that could cause what you are seeing.

    Hopefully the oil sent out had some time on it so the assessment represents reality...

  3. #3
    Join Date
    Dec 2015
    Location
    maplevalley WA
    Posts
    3,851

    Default Re: Low oil pressure & dropping with higher rpms on Lehman 120 hp twins (?)

    First do a leakdown test then a vacuum test. It could be normal wear on the crank journals and rockers? If the rings are good and the rockers dont clatter just plan on a couple rebuilds in the near future on the off season.
    It takes a nickle to go first class!
    If it aint broke dont fix it!!

  4. #4

    Default Re: Low oil pressure & dropping with higher rpms on Lehman 120 hp twins (?)

    Thanks to both makomark and kimcrwbr1 for guidance. A thinner oil (10-40) has been used for some time. Waiting on the new oil analysis but even then the oil was changed about 15 hours earlier. The engines are not clattering today. I wonder if a broken or clogged pressure release valve might cause this?

  5. #5
    Join Date
    Dec 2015
    Location
    maplevalley WA
    Posts
    3,851

    Default Re: Low oil pressure & dropping with higher rpms on Lehman 120 hp twins (?)

    IDK do they make high volume oil pumps for that engine? If there is not alot of excess blowby and the oil pressure stays consistent its a personal call. Can you remove the pans without pulling the engines?
    It takes a nickle to go first class!
    If it aint broke dont fix it!!

  6. #6

    Default Re: Low oil pressure & dropping with higher rpms on Lehman 120 hp twins (?)

    Hi. The oil sample should tell you whats going on, but at 3000 hrs it's most likely cam and crank bearings. are you using a Fram PH8A oil filter or equiv.? If you do replace bearings, change oil pumps as there are no parts avail. for the pumps which have been replaced by a new design. also change your flex oil lines to a larger inside dia. which will increase your flow and pressure by aprox. 10 or more psi.
    Charlie w

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