Oil pressure is low
 

I've got a rebuilt 400 in my bird with about 40,000 miles on it, and when I start it the oil pressure is good (~40 at idle, 60 at cruise). As the engine warms up (15 minutes or so) the oil pressure takes a dive, and winds up at 7 at idle and under 30 at cruise.

I'm running a pretty thick oil, 15w-40 with a quart of lucas stabilizer. This problem came on pretty suddenly. A few hundred miles ago it happened, and a bottle of seafoam and a quart of transmission fluid seemed to fix it, but now it's back.

Does anyone think that there is any possibility that I don't have to overhaul this motor?

What are your main bearing clearances? The chances that you have a defective oil pump are pretty slim, but not impossible. You could also have some debris suck in the oil pump check valve. BTW...40psi at idle is NOT a good thing.

Hmmm... you say it came on pretty quick, but had been fine up to that point. Doesn't sound like a bearing clearance issue to me. Sounds like an oil pump issue, and more specifically, a relief spring issue.

I don't know about an engine overhaul being required (yet), but it's probably safe to say that you're gonna need to pull the pump if no amount of Marvel Mystery Oil or the like is able to 'free it up' again.

Good luck, and here's hoping you don't have to pull the engine! :)

:confused13:

Yeah Mick,LOL.

Most of the pontiacs I've been around would be happy as a clam to have 40 psi @ idle.

But yeah,the OP said that was cold so that really does'nt mean all that much to me.

Seen plenty of perfectly healthy pontiacs with like 10-15 psi @ idle hot.

And also seen a few with less than that @ idle too.

I really dont sweat the oil PSI @ idle like some guys do.

Main thing to me is what the pressure is @ say 2500 to 3500 RPM or so,as that's when the engine is going to be seeing heavier loads,and that's where oil pumps are typically rated at for testing/diagnostic purposes.

Anyhow,the Lucas oil stabilizer product,if you look around out there you can find lots of pro/con debate about that product,myself I prefer to stay away from that additive.

Actually I try to stay away from most oil additives in general,but these days I'll concede that some of the various zinc/moly/phos additives may be needed in certain oils to account for the lack of those in the actual oil itself.

So I'm not sure how I feel about this deal right now,,,especially with the seafoam/atf mix run thru it apparently "fixing" the problem temporarily and all???

So lets clear up a few details,what brand of oil is the 15w40?

Typically that specific viscosity of oil is inteded for HD/diesel use,mostly fine for these cars no doubt,but I'm just curious what brand ya'll are using for this?

And I did'nt see it stated,,,but what were the "pre problem" hot oil pressures at idle & cruise???

I only could see the stated "pre-problem" cold pressures,and those really mean nothing to me,and then I could see that the stated "post problem" pressure @ idle is down to like 7 psi,and under 30 psi @ cruise.

Where are the oil pressure readings being taken on this engine,down at the filter adapter,or up by the distributor?

Has the oil filter been replaced during all this?

What brand of oil filter are you using on this???
(hopefully not a FRAM filter... :rolleyes:)

What sorta op guage are these readings coming from,mechanical or electrical?

Has the gauge itself (and/or sender if op gauge is electric) been checked or not?

And just what RPM are we using for the "cruise" RPM?

Bret P.

I have no idea what the main bearing clearances are at this point. They checked out OK when the motor was built.

The oil is Rotella. Before the problems started, while hot the pressure was just under 60 pounds anywhere north of 2500 rpm, with an idle pressure of 25-30 pounds. This is a mechanical gauge reading from the spot near the filter. And yes, it's a fram filter. I can't get any other brand on there with these old headers in the way.

I didn't have any reason to suspect the gauge, as the first time it happened I had a pretty obnoxious lifter tick any time I was on the interstate for more than a few minutes.

What filter?

Fram PH25

Should have a min. of 20lbs. hot @ idle , increase 10lbs. for every 1000 rpm's . Change to a good filter & see if improvement .

Do not pass go, do not collect 200.00, toss that in the trash and get a Napa or Baldwin then report back to us.

Fram filters are complete crap.

AC PF24 should fit then. Ditch the FRAM.

.

Bret and Mick,

In case you DON'T know, there is such a thing as too much oil pressure. In aircraft engines, we could actually set the desired oil pressure. In a warmed engine, 40psi @
idle is TOO MUCH,IMO. Of course, my views are influenced by my experience with aircraft engines that cost more than your house and the fact my mentor was a USAC
certified mechanic and engine builder who NEVER had a "come back". Questions?

Your point here is moot...

I say that because that's what he said the oil pressure was @ idle with the engine cold.

Not @ idle hot like you are now saying here.

And as far as I am concerned the cold oil pressure data is mostly worthless info for the sake of any discussions like this.

Fact is you did'nt bother to ask the OP what the oil pressure actually was @ idle hot before the "problems" started,and it just so happened that it occured to me that might just be an important bit of info that we actually needed to know here,so silly me I went ahead and asked the OP for that very info instead of working off of any assumptions or such.

Anyhow....

Yeah,lose the FRAM filter,I'd bet $$$$ that if this current filter were to be cut open,that the filter element has collapsed internally,and thus it's restricting the flow of oil to the engine itself,that explains everything in one nice simple answer.

I had a pretty good idea that's what was going on here,but just did'nt want to commit to that specific diagnosis until I knew for sure what filter was on here,and where the op readings were being taken,as this is a scenario I have seen before on other's pontiac engines.
(not mine though because I never use FRAM filters)

Yep,,,further proof that FRAM filters are the "orange cans of death"...

HTH

Bret P.

Bret,

You are correct. I did not express what I was thinking FULLY. I blame that on a cracked
screen that was replaced(I could only see half my screen) earlier today. 40psi COLD is acceptable; however, in my experience even that seems a little low considering my 400 NORMALLY produced 50-60 psi of oil pressure @ idle when cold. Warm idle oil pressure was 20-25psi using 10W40 and Wix oil filters. My clearances were .002 on both the mains and rods.

The gauge checked out 5 psi low, so the numbers are really more like 10 psi idle and 35 psi @ 3000 rpm. I couldn't find an AC PF24 filter locally, so I'm installing a Bosch 3423 as soon as the engine cools off.

This leaves me for now with only one question. Assuming this filter change doesn't fix the issue, would a loose clearance want a thick oil (presumably more pressure?), or a thin one (presumably more flow?)? I would think a thicker oil would be appropriate, around 50W or something. What about using a solvent of some sort? Would that just make the problem worse?

Honestly,when working on cars,you really need to get in the habit of assuming nothing.

Wait till you change the filter and see what happens,then figure out the next step.

Typically yes,generally speaking loose clearances = thicker oils and tighter clearances = thinner oils,but that's not necessarily always the case,as there are a whole lotta other dynamics that can come into play as well,such as the oil temp range the engine is operated under,as well as a few other variables,but that said there are plenty of "loose" engines out there that use thinner oils successfully,but those are generally racing engines that get much more frequent oil & filter changes (w/filters being cut open for inspection and such) and engine teardowns & bottom end inspections,so dont expect to use those engines as a guide for what's right for a higher oil change interval that a street car will use.

So long as the oils viscosity & pressure is sufficient to maintain the hydro-dynamic oil wedge in the engine bearings,then the bearing clearances are really more a concern of the engines intended useage,with a racing engine using looser clearances than a high mileage street engine would use.

And I would say no to any solvents in the oil/crankcase,IMO the only thing that's really truly meant to go in an engines crankcase is engine oil itself.

And again,worry about any future problems as they arise,not before the fact.

HTH

Bret P.

Getting a little personal there? :oogle:

...and who buys gold plated, diamond studded aircraft engines? :p

Mick,

Oh, I don't know......GE,GM,Ford,Humana,DoD,etc. Get the picture....BTW, not gold plated or diamond studded. They do use quite of bit of Cad and Nickel plating, though.
The AVERAGE cost of a PT6A(the engine I worked on the most) is nearly $1 million for a
new one, around $500,000 for a reman. You REALLY don't want to talk about what turbofans go for these days.

You must have been working a government contract with those pt6 numbers.

Nope,

The last ones I bought were in 1996. Two remaned PT6A-42 directly from P & W were
$765,000. Do the math. $382,500 ea sixteen years ago. P&W has maintained a 4% increase in prices for the last several yrs. That's $15,300 a year for the last 7 years. That's a total increase of $107,100. Added to the 1996 price of $382,500 makes a reman -42 from P&W $489,600 plus tax(estimate). NEW -42s were around $750,000 ea in 1996. Are you by chance thinking OVERHAUL PRICES from Aviall, Standard Aero, Airwork,etc? BTW....priced two OVH for -60As for the DoJ about the same time. The flat rate price (no parts BER or timed out ) was $185,000 PER ENGINE in 1996.