Low Oil Pressure

[Naj ✝︎]

Most 113s I know of peg the oil pressure gage when started from cold. As they warm up, the pressure may drop to above 15 psi at idling when hot.
This is a friend's 280 SL ( Yes, I have one ). Oil pressure at idling on cold start is below 15 psi and stays there. When warmed up, it goes over 30 psi at 2500 rpm but never pegs even at 5000 rpm.
Engine runs on 10W40 oil. Filter changed and all seals renewed.

Any ideas??? :?:

Download Attachment: Lo_Oil_Pr.JPG
44.45 KB

naj

68 280SL

[hands_aus]

Is the oil pump working properly?

Maybe worth checking the tacho thrust bush for wear.



Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[al_lieffring]

quote:Originally posted by naj

Most 113s I know of peg the oil pressure gage when started from cold. As they warm up, the pressure may drop to above 15 psi at idling when hot.
This is a friend's 280 SL ( Yes, I have one ). Oil pressure at idling on cold start is below 15 psi and stays there. When warmed up, it goes over 30 psi at 2500 rpm but never pegs even at 5000 rpm.
Engine runs on 10W40 oil. Filter changed and all seals renewed.

Any ideas??? :?:

Download Attachment: Lo_Oil_Pr.JPG
44.45 KB

naj

68 280SL

This is serious don't drive till its fixed low oil pressure.

I would reccomend attaching a pressure gage to verify that the pressure is infact that low. If it is, then;
Check the pressure releif valve behind the 22mm hex plug on the front of the motor, It's to the right of the distributor drive housing by the crank balancer.  It could be stuck in the open position.
Next would be to remove the oil sub pan and check the screen inside the oil pick up to see if it is clogged up. It is also possible that if the pan has been dented it could prevent oil from getting into the pick up. Hopefully when the sub pan is off you wont find large chunks of ground up motor components in there.

AL

66 230sl
113-042-10-014715
904/396 blue, Ivory Tex
condition: not-as-rusty-as-before-bucket

[Naj ✝︎]

Thanks, Guys,

Seems like some serious investigations needed here....

Motor is not rattly or noisy and drives real strong.

naj


68 280SL

[Benz Dr.]

Almost a sure thing that it's worn bearings. Most will have full pressure when cold and will slowly drop as the oil warms. A fast drop indicates worn bearings.
No oil pressure at idle is a sure bet.

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061

[ja17]

Hello Naj,

Remove the small sub oil pan and check for bearing metal.  You may find it in the pan and in the oil pump strainer. You may even be able to retrieve some from the oil drain plug and through the drain hole with your finger. You may also find copper specs in the creases of the oil filter if the bearings are going.

Check the oil gauge by hooking up an external temporary gauge. A damaged oil pump can also be a unlikely cause.

It could also be a "spun" main bearing. In any case most beaing problems leave metal particles behind.

Joe Alexander
Blacklick, Ohio

[rwmastel]

quote:Originally posted by Benz Dr.

Almost a sure thing that it's worn bearings. Most will have full pressure when cold and will slowly drop as the oil warms. A fast drop indicates worn bearings.

Dan,
This case seems to be the opposite.  The pressure increases with increased operating temp.

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[Benz Dr.]

Rodd, ( with two D's )

 Go back and read that post again.
It says that the oil pressure is low with a cold engine and will increase to 30 PSI at 2500 RPM but won't go any higher even at 5,000 RPM.

That's worn bearings. No mystery for me.

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061

[rwmastel]

Dan (with one N)

No, it says, and I quote:

quote:Originally posted by naj

Most 113s I know of peg the oil pressure gage when started from cold. As they warm up, the pressure may drop to above 15 psi at idling when hot..... Oil pressure at idling on cold start is below 15 psi and stays there. When warmed up, it goes over 30 psi....

So, as you can see the pressure goes up from 15 to 30 when warmed up.  This is opposite most cars that have the pressure drop when warmed up.  And as you say, a fast drop implies worn bearings.  Well, its not a fast drop, its an increase!

Are you debating oil pressure against RPM or oil pressure against engine temperature?

Naj, what say you?  What are your friend's symptoms?  Please fill out the following table:
cold engine, low RPM = ? PSI
cold engine, high RPM = ? PSI
warm engine, low RPM = ? PSI
warm engine, high RPM = ? PSI

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[Benz Dr.]

Oh, that's simple.

  The oil pressure gauge is in backwards.

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061

[Naj ✝︎]

Rodd,
Picture tells all:
Engine running few minutes from cold start (see temp gage)
Cold start mech still engaged (see rpm)
Oil Pressure: about 15 psi (see oil pr gage)

Here's what I said:
When warmed up, it goes over 30 psi at 2500 rpm but never pegs even at 5000 rpm.

cold engine, low RPM = <15 PSI
cold engine, high RPM = 45 PSI max
warm engine, low RPM = <15 PSI
warm engine, high RPM = Around 30 PSI even at 5000rpm.

Have not had a chance to look again as he is out of the country.
Game plan is to verify oil pressure with another gage, then check the oil pressure relief valve and drop the oil pan to look at a main bearing shell if the others are negative.

While searching, I found your thread:
http://index.php?topic=459

Did you ever have a further look?

naj


68 280SL

[rwmastel]

quote:Originally posted by naj

While searching, I found your thread:
http://index.php?topic=459

Did you ever have a further look?

Naj,

Shame on me for not closing out that thread!   :?   I think I ended up writing the results in a different thread.  I did visit Joe A. and got help removing the sub pan and the first main bearing cap.  In the thread you reference, Dan C. says, "Main bearing cap removal should be safe.... DO NOT remove the bearing, just look at it. It should be a dull gray with no copper showing through. It may have lines running across the face where dirt scratched the surface - you can live with that for a while probably."  Well, mine had both scratches and copper showing.  Doesn't suprise me, as the timing chain I changed a couple years ago was not an original "endless" chain, which implies a high milage engine.  Your friend's engine may be in a similar state of wear.  I still get max oil pressuse with a hot engine on a hot day when over 2,000 RPM.

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[Benz Dr.]

Hummm.....
  ( First he disagrees with me and then he uses me in a quote. I think I read the original post alright so I'm not sure..... )

 I stand by my original diagnostic. The guage is in upside down and bassackwards.

   Akmes griungf tou eth mbleopr omer ufn, ?he

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061