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Oil Pressure on rebuilt 350 HELP!

Discussion in 'The Garage' started by wed68, Feb 18, 2005.

  1. wed68

    wed68 Registered Member

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    started a rebuilt 350 a few days ago, broke it in proper, it had great oil pressure the entire break in and the first few test drives. Today I took it out for a little 20 minute drive at about 55mph and it seemed to gradually lose oil pressure eventually getting hot and losing power. I got it home ok but now it has no oil pressure at idle but the pressure will come up as the engine revs.

    Any ideas on where to start looking? It never knocked or ticked like a rod bearing spun! It starts fine just has no pressure at idle.

    Bill
     
  2. wraenking

    wraenking 1/2 ton status

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    oil pump? did you replace that with the rebuild? not even sure you can replace, just taking a stab
     
  3. Silver84k5

    Silver84k5 1/2 ton status

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    did you tack weld, or use the bracket that holds the Oil pump pickup tube, in the pump?

    are you using the stock GM oil pressure gauge? Is it the electrical style, or the tubing style?
     
  4. ryoken

    ryoken Puppy Fabricator Premium Member GMOTM Winner

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    might wanna throw a cheap mechanical on it to confirm your readings...
     
  5. wed68

    wed68 Registered Member

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    Yes I changed the oil pump with the rebuild! I am going to put a mechanical on it soon to check it, no I did not tack weld it or use a bracket could it have came off?



    Bill
     
  6. Silver84k5

    Silver84k5 1/2 ton status

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    it could have, i dunno how likely it is though as it sounds like you have not ran it much... Check it with an aftermarket gauge first... If it still persists then drop the pan and check the pickup... if that checks out ok, then i dunno what else to do but start taking **** apart hehe.. Good luck
     
  7. adamforsythe

    adamforsythe 1/2 ton status

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    This very same thing happened to me. The fix: I put in 10W 40. My engine hates 10W 30. At idle and going down the road I would lose all oil pressure. When I would kick the 4 barrel in my oil pressure would go way up then come right back to 0. This may be your problem this may bot be your problem. But if I was you I would check it out.
    Thanks
    Adam
     
  8. Jonny-K5

    Jonny-K5 1/2 ton status

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    if you lose oil pressure as it gets hot your main bearing clearances might be too big. i
    ve been told this is the #1 reason for loss of pressure at running temps. i had this problem before with new rebuilds. but in my case it was on an oddball 340 buick thats needs super tight bearing specs. the rebuilder set it up to 350 buick specs, which is double the gap that i needed. pretty unlikely with a 350 since they are so common. but if you did it yourself that might be what to look for.

    you can bandaid fix it by installing a high volume(not high pressure) oil pump, if it isnt in there already.
     
  9. wed68

    wed68 Registered Member

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    I may have to try the high volume oil pump if I can not find the problem! The machinsts at the shop that did my heads and bore job, miked the crank and they were still in standard specs so I went back with new standard bearings. The oil pressure was good on the first few starts, now it is 0 at start up when cold!



    Bill
     
  10. Jonny-K5

    Jonny-K5 1/2 ton status

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    if its zero when cold you may have a problem w/ oil pressure sending unit. either that of something serious inside. a high volume pump will only work if it loses pressure when hot, but has good pressure cold.
     
  11. Fierospeeder

    Fierospeeder Banned

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    do you have the stock oil pan, and is the pickup also stock?


    sometimes the oil pump comes with a gasket and it prevents the pump from sucking in air.

    Double check your oil filter, see if your getting oil in there. Maybe it got clogged.


    Did you get a chance to plastigate the bearings?
     
  12. SUBFAN

    SUBFAN 1/2 ton status

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    Check the oil for gas or coolant....I had a fuel pump diaphram let go once, and it pumped gas into the oil. An oil pressure gauge saved that motor....


    You must measure those bearing clearances....
     
  13. Thunder

    Thunder 3/4 ton status

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    Sounds like a Main or Cam bearing problem. Did you put a performance cam in it? If you did. Did you check for coil bind? if
     
  14. mrk5

    mrk5 The Sticker Guy Moderator Vendor GMOTM Winner Author

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    I would also recommend the mechanical gauge. I was told by my engine builder that they have customers with electric oil pressure gauges coming back freakin' out about a lack of oil pressure, and they tell them to get a mechanical. Then with the mechanical gauge oil pressure is just fine.


    The fact that the engine gets hot is suspicious. Does oil pressure drop before or after the engine gets hot?
     
  15. wed68

    wed68 Registered Member

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    Update! I change the oil today to 10w40 but no change. I did find pieces of what looked like bearings in the oil filter. When I started it cold it had good pressure. I then found an oil leak on my sender unit, I changed it but the same thing little pressure at idle but about 30 psi while driving!

    Bearing spun?
    Oil pump came apart?


    Bill
     
  16. FWP

    FWP CRS

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    Drop the oil pan, pull the main caps and maybe a rod cap or 2, and take a look. That's what I would do. HTH
     
  17. wed68

    wed68 Registered Member

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    I dropped the pan and found what I had been expecting, all bearings rod and main were scarred bad! I will pull the engine and start over, new crank and such!

    What could have caused this, I believe that due to the fact that all bearings were scarred that I must have started the engine with trach still in it, I pulled the ultimate f>>> up I did not clean the oil gallerys before assembly, I thought the vat was enough!

    I will keep yall posted!

    Thanks for the Help!

    Bill
     
  18. adamforsythe

    adamforsythe 1/2 ton status

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    Dude that sucks. Keep us up to date on what is going on.
    Thanks
    Adam

     

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