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Thread: Oil pressure problem in Isuzu Diesal

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    Default Oil pressure problem in Isuzu Diesal

    Gudday all,
    I have NRP200 with a 4hf1 motor. When i first bought it (SH), after I got it home the oil pressure took a long time to come up, more than10 seconds. I Changed the oil, removed the sump and thoroughly checked the pick up tube. I tested the oil pressure and it had heaps. The problem has only occured once in a blue moon until recently, now it happens morning and night. It is worse at the end of work than in the morning. Just wondering if any one else has had this problem.

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    classic symptoms of a sticky oil pressure relief valve (weak spring) I would look there first . how many KMS on the engine?

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    Quote Originally Posted by Nifty363 View Post
    I tested the oil pressure and it had heaps.
    How did you test it? with a gauge?
    What pressure did you get?
    You need to test it with an accurate gauge to see if you have a problem with your engine or your instrument gauge or light.
    What brand of filter are you using? Cheap filters sometimes have crappy anti-drainback valves.

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    On some engines ive worked on it was the oil pressure sender playing up, replaced it and all was well.

    Add that to the list of things posted above me.....

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    Years ago I found a brilliant way to test the oil pressure by removing the rocker cover on the motor.
    I had not long replaced the original 4 cyl engine with push rods to a 6 cylinder with an Overhead cam and this was the first time I had removed it since it was installed to check the valve gap so I did what I had done with every other push rod motor, took off the cap and started the engine..............
    This was the first and last time I ever did that as by the time I moved from beside the A pillar to look under the bonnet to see about 500 gallons of engine oil happily spraying everywhere before I could turn the engine off.
    I didnt know the cam was under pressure did I?
    Last edited by gordon_s1942; 06-02-17 at 03:59 PM.
    I stand unequivicably behind everything I say , I just dont ever remember saying it !!

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    hey mate either the oil thinned out too much or you have put the wrong grade oil in? the other thing to ask is how many km's does your NRP200 have on it?

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    A sticky relief valve certainly makes sense, I shudder to think how hard it will be to get at, no the oil pump is not accessable from the sump. These motors actually have two oil pressure relief valves, one at the pump and one in the front of the motor, that is easy to get at. I once had one of these motors that had excessive oil pressure and the relief valve at the front was responsible. ( this time thou I'm sure that the one on pump would be the one, if this is the problem). Its done about 330,000 km. I use Fleetguard filters. ( I once had a Subaru which did a similar thing and the dealer said "I know it sounds like BS, but use a Subaru oil filter, he was correct, I was using Ryco" I use correct grade of good oil so thats not the problem. I used a guage to check the oil pressure, the sender is OK. Thanks every one. I think I might try a oil additive to see if it makes a difference, if so that points to the sticky relief valve. I would like to be able to get a diagram of the oil pump so I could find out how hard it is to get to.

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    Quote Originally Posted by Nifty363 View Post
    I would like to be able to get a diagram of the oil pump so I could find out how hard it is to get to.
    Does help?
    Never stand under a shadow that's getting bigger

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    Thank you very much Antennaman, The relief valve is out the front of the motor in a easily accesable spot, so I will get one and see if it solve the problem. i will let you all know how it goes.

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    Its barely run in at 330K.

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    I have replaced the Oil Pressure relief valve, but unfortunately the problem is still there, will have to keep searching. there are some Orings behind the oil filter which I will check next weekend.

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    I put some Lucas Oil in a few months ago and the problem disappeared until last week, now the oil pressure will not come up at all. So I will have to pull the oil pump out and check it problem out. Will let you all know the result. Won't be for at least a month. I put recondition the gearbox while I have it out. Antennaman do you have a diagram of the gearbox?

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    I'd be pulling the sump and checking the oil pickup, they are prone to cracking and breaking

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    Thanks Rick, but have already done this, and all the other easy to get at things. About the gear box, I have to indentify it to get parts, but the id plate is gone. Does anyone know how to identify it from the VIN No?

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    is it the 6 speed box? or AMT
    Last edited by Rick; 09-06-17 at 08:15 PM.

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    It is a 5 apeed. NPR 200 only a small truck, 4500kg GVM. I am having trouble identifying the box, as there a few different boxes. The plate on the box has gone. I am hoping that the trans code on the manufacturers plate will be able to identify it, but even the local Isuzu dealer has so far not been able to help. So far no gearbox repairers are not interested in supplying parts.
    At this stage, the only way I could order the parts is the dismantle the box and measure all the bearings and seals.

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    Gudday All, I have finally got my truck going again today. All good. Oil pressure again. I replaced the oil pump. Only thing I noticed was that the new oil pump had a change in design for the relief valve. The old one had a piston and the new one had a ball bearing. I am highly suspious that there has been some trouble with the piston sticking and that is why they changed the design. I figure if they had not had problems they would not have changed. Any way thanks to all who have helped and if some one else out there has the same problem this is worth looking at; but do check the easy things first as changing a oil pump is a big job. Gear box, cylinder head, fly wheel housing all have to be removed.
    Regards
    Mike.

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    How did you get on with your cog box, were you able to rebuild it? How did you go getting the parts?
    I'm out of my mind, but feel free to leave a message...

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    I bought a second hand box as the parts were horendously expensive. The Isuzu dealer was able to identify the box.
    Regards
    Mike.

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