2.9L loses oil pressure when warmed up

[Sevensecondsuv]

I've got a 90 ranger with the 2.9L. The engine was rebuilt 20,000 miles ago and runs great. Anyways, just recently it started acting up. When the engine is warm and you let it idle in gear the oil pressure drops off. The top end taps pretty good when it's warm too.

Anyways, I quit driving it as soon as I noticed it. I just now finished putting a new oil pump in it (took all day + 100 bucks in parts) just to find out that it changed nothing!

So it has been rebuilt 20000 ago, has a new oil Melling oil pump, has a new motorcraft oil filter, the oil pickup tube is clean and clear, and is full of 10W30.

The truck does not burn oil and runs really nice aside from the recent oil pressure problem. It leaks some but not much more than any other ford truck of that vintage.

What the #### is going on here? I need this thing fixed!

 

[MAKG]

IF it's really low (use a mechanical gauge, not stock), it's likely engine bearings -- specifically cam bearings on a 2.9L. Pumps do not make pressure. Whatever they are acting against (oil clearances) makes pressure. Pumps just make volume.

 

[Sevensecondsuv]

As a mechanical engineer, I'm plenty familiar with pump curves.

I have a hard time believing it's engine bearings as the thing was rebuilt 20,000 miles ago.

 

[mike327]

Sounds like bearings to me. Try a thicker oil like 40 or 50 weight. Did you check the clearances after the machine shop?

 

[Big Jim M]

As a mechanical engineer, I'm plenty familiar with pump curves.

I have a hard time believing it's engine bearings as the thing was rebuilt 20,000 miles ago.

If the gauge drops off and the top end starts clacking...you don't need another gauge! The top end is telling you the gauge is correct.
So you have an internal oil leak.. As a mechanical engineer where do YOU think the leak might be?
Everyone reading this thinks it is worn bearings.. give us your thoughts.
I don't know your engine but most engines have the pressure sender located near the pump itself.. So the pressure reading is for the entire engine. If the lifters are clacking I'd PARK her for sure. No sense ruining the crank while you are thinking about it.
Big Jim

 

[IMenriched]

yes, it could be the bearings are wearing excessively.....that seems extreem.
Could be that the valve train has loosened, the main stands that hold the rocker arm shaft. Were those rocker shafts cleaned before reassembly?? (presuming that you had them off, of course.

and it been said in other posts/ threads that sometimes they just tick.

but definiatly don't trust the factory sending units for true readings...a set of mechnical guages will give more accurate feedback.

 

[almostclueless]

Apparently quite a few shops "rebuild" engines without replacing cam bearings. This is an alleged source of pressure loss in particular for the 2.9

 

[MAKG]

Sounds like bearings to me. Try a thicker oil like 40 or 50 weight. Did you check the clearances after the machine shop?

BAD idea.

Oil pressure is determined mostly by the loosest clearances. Thicker oil will hose the tightest -- with no warning until one breaks. It's hardly a good idea to hog out the rod bearings and/or lifters in order to plug up cam bearings.

 

[Sevensecondsuv]

OK sorry for all the confusion. The engine was rebuilt before I bought the truck last december (I got it for $400 with a bad tranny leak that is now fixed). I've only put about 4000 miles on it. Therefore I know no specifics about the rebuild.

I know the difference between ticking and tapping. Every 2.9L I've ever heard ticked. This one taps. I don't need a mechanical gauge to tell me that there isn't enough oil pressure.

I have not been driving it since this happened. I guess I'm just trying to deny the obvious - that there is something wrong internally with the bearings or oil passages. Must have been a pretty bad rebuild they did.

I might consider replacing the cam bearings if I knew for sure that those were the problem. One thing is for sure though, the engine isn't coming out of the truck and getting torn apart. This truck just ain't worth the time and effort.

The 20w-40 is sounding like a good idea right about now .... until I muster up the desire to change the cam bearings (might take several months).

 

[90B24wd]

+1 on the mechanical oil pressure gauge
Also check out your rocker armshaft to see if it is not cloggeed up with
dry sludge. It's alot easier and cheaper thing to do than changing your cam bearings.

 

[AllanD]

The rocker shaft being "plugged up" would not result in ticking

ticking would result from the LIFTERS being oiil starved
and they get their oil from the main bearing oil gallery.

The rocker shafts would probably last thousands of miles if
you filled them with RTV before installing them... that's the
beauty of shaft rockers tey don't need a constant supply of
oil to continue working.

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