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Technical Very Low Oil Pressure Question

Discussion in 'The Hokey Ass Message Board' started by Belair348, Jul 12, 2015.

  1. Belair348
    Joined: May 14, 2007
    Posts: 27

    Belair348
    Member
    from Lizton, IN

    Hello,

    I've got a 348 that I've rebuilt, new oil pump, and everything seems to be OK, except my oil pressure. To start I'm currently running 10W-40 and at start up I have about 50 - 52 lbs of pressure. However after getting the engine up to temp and driving 20 or so miles my pressure drops to about 1 to 2 lbs at idle.
    The engine isn't running hot, nor do I hear anything out of the norm. It's a flat tappet, so I wouldn't hear the lifters, but overall it doesn't sound any different when it's dropped.
    I've tried 2 different gauges with the same result.
    I've got the gauge connected to the port right above the oil filter. I've added the spin on adapter if anyone thinks that could make a difference.
    I found this thread, but it didn't come up with to many ideas on why it could be low, but it did talk alot about why some people don't like Pennzoil.
    http://www.348-409.com/forum/threads/oil-pressure.63/

    Any ideas on how to proceed would be appreciated.
     
  2. flathead4d
    Joined: Oct 24, 2005
    Posts: 888

    flathead4d
    Member

    Try some 20W-50. I use Castrol but any major brand will do. I don't know much about 348's but my FR flathead does the same thing. Starts about 50# until it warms up and drops to less than 10# at idle. With a flathead it's more about flow than oil pressure. Not sure if that's the same with a 348.
     
  3. oldolds
    Joined: Oct 18, 2010
    Posts: 3,153

    oldolds
    Member

    I would guess you have a bearing clearance issue. When things warm up somewhere there is too much space. Cam bearings is the usual problem area.
     
    40fordtudor, 302GMC and sunbeam like this.
  4. Engine man
    Joined: Jan 30, 2011
    Posts: 3,476

    Engine man
    Member
    from Wisconsin

    If you don't run it in the cold you don't need a multi viscosity oil. We ran extra clearance in our racing engines and the pressure would be low at idle. We ran 40 weight Valvoline racing oil back then but it might be difficult to find straight weight oil now. Valvoline VR1 is made in 30, 40, 50 and 60 straight weight and has the zinc needed in older style engines. We also ran Melling high volume pumps with a 60 psi relief spring so the pump could supply more oil at idle. I think a high volume pump is available for W engines but you might have to build a pickup tube.

    I'd try the 40 weight first to see if it helps then go thicker or thinner as needed. 30 weight would have been the standard engine oil at the time those engines were built.
     

  5. Someone correct me if I'm wrong. But I don't think that you gauge your oil pressure at idle. I think that you gotta run it up to 1000-1500 RPMs or something like that.
     
  6. What did you set your bearing clearance at? if you set it up loose you'll probably need to go to a high volumn pump and if you don't know your bearing clearance you just learned a hard lesson.
     
    40fordtudor likes this.
  7. Blue Coupe
    Joined: Oct 11, 2009
    Posts: 58

    Blue Coupe
    Member

    Our engine builder taught us, 10 lbs of oil pressure for every 1000 engine rpms. Sounds like pump/bearing issue.
     
    jakespeed63 and Hdonlybob like this.
  8. porknbeaner has it right ....
     
    40fordtudor likes this.
  9. King ford
    Joined: Mar 18, 2013
    Posts: 1,466

    King ford
    Member
    from 08302

    If heavier oil gets you up to 10 or so at idle and you have 20 or more and no noise when you speed it up above 1000 rpm I would run it but listen and watch your gauges closely .....
     
  10. models916
    Joined: Apr 19, 2012
    Posts: 380

    models916
    Member

    348 has a drain back issue with high volume pumps. Lots of oil is going to go up top where the only way down is over the cam. The 409 got a large hole in the china wall to timing chain area for that reason. 409 pan is 6 qts, 348 is 4 unless it's the truck pan (drain plug facing down). At the very least I would go to heavier oil. If you go to he high volume pump, keep the pressure at the normal setting and drill the hole in the front to the timing cover. Maybe 20/50 with a can of STP. If your at 10 psi for every 1,000 rpm when driving, you're probably going to be ok. Stock pump's short gears don't pump much oil below 1,000 rpm.
     
  11. models916
    Joined: Apr 19, 2012
    Posts: 380

    models916
    Member

    P.S. could also a try a tighter micron filter. My K&N will drop my idle psi about 5lbs.
     
  12. I'll second the 20W-50 recommendation or even a straight 30W. 30W was the 'normal' oil back then, those motors weren't designed for thin multigrades. The 302 in my avatar had 5W-30 in it when I got it and didn't like it; had low oil pressure and noisy valvetrain. A switch to 10W-30 (which it was designed for) made a difference.
     
  13. Hemiman 426
    Joined: Apr 7, 2011
    Posts: 650

    Hemiman 426
    Member
    from Tulsa, Ok.

    porknbeanerX100... if the clearances are off, running a heavier weight oil is only going to delay the eventual failure.. We had the same problem with an 0t car running a sbf. fresh overhaul and the shop supposedly clearanced everything and ordered the correct bearings.. Nope, initial fire up showed low oil pressure. pulled the engine and found way too much clearance on the rods and mains. Correct bearings did the trick and that engine is one strong sucker. Better safe than sorry!
     
  14. Gman0046
    Joined: Jul 24, 2005
    Posts: 6,260

    Gman0046
    Member

    I'm continually amazed when folks suggest using high viscosity oil to raise oil pressure. All that does is mask the real cause of the low pressure. A rebuild is the only true repair.

    If you really want to increase the oil pressure fill your crankcase with Motor Medic or stretch your oil pump spring. These two "fixes" make about as much sense as using high viscosity oil.

    Before I'd do anything I'd hook up a direct reading oil pressure gauge to verify the accuracy of your oil pressure indicating system.

    Gary
     
    Last edited: Jul 13, 2015
    wedjim likes this.
  15. 4thhorseman
    Joined: Feb 14, 2014
    Posts: 261

    4thhorseman
    Member
    from SW Desert

    Pull it. Redo all bearing clearances. Reinstall it.
     
  16. Oldbill51
    Joined: Jun 12, 2011
    Posts: 284

    Oldbill51
    Member

    Another thing to check is whether you might be flooding your fuel system with too high a float level, stuck float, or misadjusted choke. It doesn't take much gas in the crank case to really thin out some oil. Pull your dip stick and smell give it a smell.
     
  17. Jimmy2car
    Joined: Nov 26, 2003
    Posts: 1,707

    Jimmy2car
    Member
    from No. Cal

    A change of oil isn't going to do it. Find the problem and fix it
     
  18. Years ago, I built a BB Chevy, for my Nova SS. Thought it was good idea to take the reading at the port, above the filter. Wrong! When a reading was taken at the top port, behind distributor, it was almost zero. The engine was always a bit noisy and oil pressure was low when it warmed up. Turns out Me and my buddy left out one of the plugs, behind the cam sprocket. What an expensive mistake.

    Also, about 5 years ago, I rebuilt a 394 Olds. Had some issues, getting it to run right, on the initial fire-up. Long story short, I ruined the camshaft, by not breaking it in properly. All those metal particles, found their way into the bearings. That was a customer's car and it cost me a big pile of dough.

    Flat tappet cams MUST be broken in at the proper RPM and run there for at least like 30 minutes. Then it's a good idea to dump the oil and filter. Then cut open the filter and see what's inside. When I was at the Porsche race team, we cut open each and every oil filter, that came off the engines. After being run at full throttle for 3, 12 or 24 hrs, no stone was left unturned.

    The 350 that's in that Nova now, makes like 80psi, when cold on 30w oil. It has a hi-volume, hi-pressure pump. I regret that decision, for a street motor, robs valuable HP. The 10 psi per 1,000RPM rule is true. Unless your are building a long distance race engine, stay with a good stock oil pump. That 394 purrs like a kitten to this day.
    Why do I know allot?? Because I've made a bunch of mistakes.

    One last note: Brad Penn makes a terrific 30w break-in and regular duty oil. Has all the correct additives for old cars. About $8 a qt, but cheaper than another rebuild. Can get it by mail order.
    Good Luck.,
    JT
     
    wedjim likes this.
  19. Belair348
    Joined: May 14, 2007
    Posts: 27

    Belair348
    Member
    from Lizton, IN

    Thanks everyone for your suggestions.

    As for clearances, all rods and mains were checked and were within specs. I don't remember the numbers right off the top of my head, but I wouldn't have continued if something was off. Cam bearings however were installed by the shop that did the machine work. Those clearances were taken for granted, probably a mistake at this point.

    I'm going to look into the drain down issue that Models916 suggested, and if that doesn't fix the issue, it might be coming out this Fall for further inspection.

    Thanks again
     
  20. models916
    Joined: Apr 19, 2012
    Posts: 380

    models916
    Member

    Try taking a pressure reading up front on the passenger side right between the timing cover and the intake manifold. That is the end run of the pressure galley for the lifters. That should tell you something. Small 1/8 plug there.
     
  21. models916
    Joined: Apr 19, 2012
    Posts: 380

    models916
    Member

    Another issue I've seen was if the pump pickup was welded on when the pressure spring was still installed. It will loose its temper. Call me if you want. send a message and I give you my number. I've had plenty of the w engines appart through the years. Mike
     
  22. Engine man
    Joined: Jan 30, 2011
    Posts: 3,476

    Engine man
    Member
    from Wisconsin

    Using oil thinner than the motor was originally designed for can cause low oil pressure at idle. Even then, the oils were a compromise. You had to change to thinner or multi viscosity oil for cold temperatures and thicker straight weight oils for warm temperatures. When the oil pressure is fine at even slightly higher engine speed, it's a pretty good sign that the oil is too thin.

    If a motor isn't being operated at below freezing temperatures, a straight 40 oil will be fine.

    Stretching the oil pump spring only raises the bypass pressure. The bypass valve isn't opening at the low pressure. Using a high volume low relief pressure will allow the pump to dump oil to the pan at higher rpm to prevent the oil return problems. 50psi relief would be plenty. You won't turn a stock W block much over 5,000 rpm for long and there isn't really a reason to. These are torque engines.
     
  23. metlmunchr
    Joined: Jan 16, 2010
    Posts: 762

    metlmunchr
    Member

    I've seen quite a few Chevy small block oil pumps, both stock and aftermarket replacement, where the clearance between the rotors and the cover plate is way bigger than what the factory specs call for. Also seen a lot of bottom covers that look like they were face milled with a cutter made up of broken carbide inserts and dull rocks. Either of these conditions will let the oil bypass within the pump at idle to the point where the pressure is near zero.

    Both problems can be fixed with nothing more than some 60 to 80 grit waterproof sandpaper and a piece of plate glass about a half inch thick to act as a flat surface plate.

    If the surface finish on the cover plate looks like hell, that will be obvious. Work it down to smooth and flat with the sandpaper laying on the glass.

    For the rotor clearance put a straight edge across the bottom of the pump housing and check the clearance with feeler gages. GM service or overhaul manual will have the clearance spec. I'm thinking .002 to .003 on a small block pump, but its been a long time so don't use that as a good number. I've seen them with as much as 3X the specified clearance. Anyway, if the clearance is too big, you have to work the housing down on the glass and paper until it measures correct with feeler gages. Once the pump is out, the entire job takes about an hour if you have to work both pieces.

    I first did the above on a stock pump in a 350 horse 350 about 40 yrs ago after reading a magazine article talking about too much clearance in Chevy oil pumps. Engine had about 75K miles and never had held decent idle pressure with 10W30 oil at operating temperature. Still have the car and the engine, with about 125K miles on it now. It'll still hold 30-35 psi at idle with the engine at normal 180* operating temperature, the same as it did right after I reworked the pump housing and cover.
     
  24. pdq67
    Joined: Feb 12, 2007
    Posts: 787

    pdq67
    Member

    Years ago I did a "Krylon" overhaul on my 260 SBF engine that I put in my '64 Fairlane 500 SW.

    The oil light would barely flicker at idle hot with either 30 or 40wt in it, (I forget which?), but at rpms, held pressure fine.

    I ran my thumbnail along the main and crank throws and could feel the circular ridges, but said to myself, the old beater ran fine before I tore her down so ta heck with any crank work. And I ran her that way for years, BUT I NEVER , EVER beat on her!!

    pdq67
     
  25. Pewsplace
    Joined: Feb 10, 2007
    Posts: 2,797

    Pewsplace
    Member

    I have the same problem with my Edelbrock Signature Series 460hp engine. The idle pressure is about 5-7 pounds but runs at 25 -30 pounds while cruising at 70 mph. Edelbrock told me that is how they set up the engines to get more engine oil to the bearing surfaces and told me not to worry….25,000 miles later the $10,000 engine still runs perfect with low oil pressure at idle. I, like you, always thought the more pressure the better for the engine but so far Edelbrock has been correct. I run the race filter by WIX which also lowers the pressure and increased the flow.
     
  26. Gman0046
    Joined: Jul 24, 2005
    Posts: 6,260

    Gman0046
    Member

    I've heard the same thing about flow vs. pressure but it sure feels good when I look up and see 30-35 # of idle oil pressure.
     
    buickfunnycar.com likes this.
  27. I think I could liove with a small block that ran in the 7 PSI range if it made 30+ cruising. The problem with the @Belair348 motor is it is only hold about 2psi. That would concern me in about any mill I owned. As @metlmunchr mentioned and something that slipped past me is oil pump clearances themselves. I normally run Melling pumps and suggest them to anyone I build for, I came up knowing that you have to check clearances in the pump even if it is new and have even found brand new Melling pumps that needed a little help. That is a good call.
     
    Truck64 likes this.
  28. wedjim
    Joined: Jan 1, 2014
    Posts: 420

    wedjim
    Member
    from Kissimmee

    The scary part is, the longer its run, the more the repairs might cost. But oil pressure is a factor of resistance. So heavier oil will raise the gauge, but good bearing clearances are what's really needed for longevity and oil pressure indicates their condition.

    Modern engines run 0-20 oil and make plenty of oil pressure. They are machined very well, even for mass production.

    Heavier oil is a used car lot strategy, or to get home from a local show, imo.
     

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