C-12 oil pressure low on 1999 freightliner century

Discussion in 'Trucks [ Eighteen Wheelers ]' started by Rasim, Sep 10, 2016.

  1. Rasim

    Rasim Light Load Member

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    My oil pressure gauge reads 28-30 while bobtail at 65 mph and coolant temp stays at 180-185 degrees. Just bought the truck so not sure how it will do under a load. At idle i get 20psi oil pressure. As i drive the truck sometimes the check engine and engine protect light comes on and goes off usually when i release the gas paddle and the low oil pressure indicator on the cluster will flash. Truck runs really good has lots of power and no smoke or shaking during idle nor driving. The low oil pressure and check engine lights will come on and go off after couple of second....please someone knowledgable would be very appreciated thank you.
     
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  3. maggard359

    maggard359 Medium Load Member

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    Start with an oil pressure sensor, or hook up a manual gauge to verify. A faulty sensor will give the symptoms you have. If that checks out you will be needing to drop oil pan and replace oil pump and probably mains and rods while you are at it.
     
  4. baha

    baha Road Train Member

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    Plus change the oil 1st thing, even if someone told you oil was just changed have a oil ali. done even if you have to mail in a sample kit you bought at parts store?
     
    Steel Tiger Thanks this.
  5. AModelCat

    AModelCat Road Train Member

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    That seems a little low for a Cat. First thing I would do is change the oil to make sure you have the proper oil since its a new to you truck. Take an oil sample first though. Fuel can sometimes dillute the oil, thinning it out and reducing oil pressure. An oil analysis will indicate that. Then plumb a test gauge into the engine like stated above AND compare that to Cat's oil pressure specs. If it is indeed low, it could be worn out bearings, weak oil pump or possibly a sticking oil pressure relief valve. If oil pressure is good, look at the sensor/wiring/gauge.
     
  6. wore out

    wore out Numbered Classic

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    What is the pressure when it's first started after sitting say over night.
    If it's up to say 60 or better but gradually falls till it sets of the low pressure alarm most likely it's rod bearings. The top half wears faster than the bottom. It will fall faster pulling a load than empty. If one of the tubes from the pump to the block are sucking air it will do that as well.
    If it is just generally low like it is now it's very possible that the oil pressure relief valve on the pump has trash on it or is bad. The bypass valve could also be stuck open.

    Run it with the valve cover off and look for a high pressure leak in the top, that will cause low oil pressure as well.
     
  7. Rasim

    Rasim Light Load Member

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    All of your commenst are highly appreciated. The sensor looks like it is fairly new and there is no oil leeking around it. If its the main rods bearings i suppose that is the most expensive fix, would the truck experience any other symptoms besides low oil pressure? Also with oil pump, and fuel in oil? Would that cause a lot of smoke out the pipes?
     
  8. Rasim

    Rasim Light Load Member

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    Pressure on start is 20 psi
     
  9. sliver

    sliver Light Load Member

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    If it's only 20 psi after sitting all night and motor is cold. You have some issues that need addressed asap. In my opinion
     
  10. sliver

    sliver Light Load Member

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    Did you have this truck looked at by a mechanic before purchasing? Did you test drive it? Or even start it? Buy it sight unseen? Or just drove up saw it and had to have it?
     
  11. Rasim

    Rasim Light Load Member

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    Test drove it yes but this thread is for finding the issue not weather i did this or that prior to buying no offense just trying to see your opinions of what it could be
     
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