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Oil pressure question???

Discussion in 'The Garage' started by CaveBlazin, Aug 6, 2002.

  1. CaveBlazin

    CaveBlazin 1/2 ton status Premium Member

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    Ok my dads got a 91 0r 92 Chevy Silverado and he says that his oil pressure goes down about 5 minutes after he drives it now this is something new it usually runs around 40 or 45 now it drops to like 15 or 20. He changed out the sensor the other day and it still does it. He took off the valve covers and she's spitten oil. Anyone got any ideas O yeah its a 350 I believe TBI engine. Any ideas will be great. Thanks
     
  2. Dieselmh

    Dieselmh 1/2 ton status

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    Is he running 10W-40 or 20W-50 oil?
     
  3. SkulzNBonz

    SkulzNBonz 1/2 ton status

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    I've got an '86 w/ a 305 thats starts out at close to 60 psi, and after it warms up pressure fluctuates around 30-35 psi. Running 10w30. Has your dad had an oil change lately? I noticed a couple of weeks ago my pressure started to drop into the 20 psi range, changed the oil, and it went away.

    John
     
  4. Dieselmh

    Dieselmh 1/2 ton status

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    Here is what I was getting at. The 10W-30 rating shows the variable viscocity. It is normal for the oil pressure to drop when the engine heats up because the oil is getting thinner. It shouldn't drop below 12 or 13 which I believe is an acceptable number. Your oil pressure will also drop as the engine gets older because of an increase in cam and crank bearing tolerances. As the engine wears, the tolerances get larger, therefore the oil isn't restricted as much which lowers the pressure. There is also a small chance that your oil pump is starting to fail, or the pickup is clogged, but it's doubtful since it works fine at higher rpms. If you're really worried about it, you can first take a mechanical oil pressure gauge and temporarily replace your electric one. If the mechanical gauge reads the same as the electric, then you at least know that your reading is correct. If it's only dropping to 15 at the lowest, then he shouldn't have any problems. His truck sounds just like my daily driver. If the oil pressure drops too low, the computer will kill the fuel pump in order to save the engine. It's probably always dropped a little, and over time has started to drop a little more and he just now noticed it. I don't think it's anything majore.
     
  5. BIG STEVE

    BIG STEVE Registered Member

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    Ive seen big honken diesals pulled because of a bad gauge
    that was good advise to get a good manuel gauge and recheck it ive seen engs. run forever with 20psi max.
    also check oil leval an over filled crank case will result in oil psi drop- right dip stick?
     
  6. CaveBlazin

    CaveBlazin 1/2 ton status Premium Member

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    Im pretty sure he runs 20-50w oil I'll tell him about the change to the manual sensor. If yall have any other ideas just give it a post thanks too all....
     
  7. uglychevyZZ4

    uglychevyZZ4 3/4 ton status

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    </font><blockquote><font class="small">In reply to:</font><hr />
    goes down about 5 minutes after he drives it now

    [/ QUOTE ] this is something normal, as he explained, gets thinner, but if it is a drastic overnite change, id say maybe poss bad oil pump, or a bearing going south? </font><blockquote><font class="small">In reply to:</font><hr />
    He took off the valve covers and she's spitten oil.

    [/ QUOTE ] all sbc spit oil when the covers are off and its running, thats why you use rocker oil deflectors /forums/images/icons/laugh.gif

    </font><blockquote><font class="small">In reply to:</font><hr />
    it usually runs around 40 or 45 now it drops to like 15 or 20

    [/ QUOTE ] I disagree with a previous post ( no offense /forums/images/icons/laugh.gif ) but anything below 20.lbs. ( even with 10-40w ) at idle when at normal operating tempature is suggesting WEAR and milage are becoming a factor with probably a bearing or a pump. if it was gradual id say think future rebuild maybe 1-2 years, but since you have expressed this is a SUDDEN change i must say take more note to this drop.
    I'd do as he stated and try a manual guage first, and make sure you are not wasting money, if thats not it, I'd say think soon lower end check.
    Rob...
     
  8. CaveBlazin

    CaveBlazin 1/2 ton status Premium Member

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    Ok here's some updated info on the truck. Now he says its dropping all the way down to Zero after a little drive. I told him what yall said about a manual gauge and he's gonna try it today and see. I think it might be the oil pump. Isnt there a sensor that kills the fuel pump in case the pump fails??? O yea also its an 89 dont know if that'll make a difference or not. If he has to replace the oil pump do you guys know if he will have to lift the engine a little. I know in my blazer I didnt the oil pan just came right off. thanks again guys
     
  9. CaveBlazin

    CaveBlazin 1/2 ton status Premium Member

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    ttt.... need help please on the updated info Thanks yall
     
  10. FunBlazer

    FunBlazer Registered Member

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    Change the oil sencor by the oil filter, mine did just that and I changed the top one first, still had the problem, changed the bottom one and my problem went away.
    I am gonna have to disagree with one of the previous statements, 15psi of oil pressure is fine(it does not mean that your engine is going south) If you look in any chevrolrt overhaul manual it says 15psi at idle(750rpm's) is fine(when hot). My camaro holds 60psi cold and 18psi hot, 350-Lunati .585 lift solidlifter cam, Dart iron eagle 230 heads, tunnel ram, 2 750 carters, 11.5-1 comp. and that motor gets shifted at 7200 all the time(4-spd car) and runs 11.88@113mph in the quarter mile, and its been together for 3 years and the oil pressure has always been around 18psi hot. Back to the question at hand, change the sencor by the oil filter and you'll have good oil pressure again.
     
  11. mdm365

    mdm365 1/2 ton status

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    I had this problem with an 81 blazer and the oil pump pressure valve was stuck open.It took two hours to pull the pan and pump run to the parts house and put it back together.just an idea for you.
     

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