odd 4age oil pressure issues. up and down in pressure.

[andrew_mx83]

Do you have a dial indicator and a spare block? You can do a ghetto straightness check that way for nix.
You can also linish the crank journal yourself to a certain degree with scotchbrite pads, and lots patience. The key is to do it evenly and not make low spots or ovality. You wont get deep scratches out but small ones, maybe.
In reality it will still run with a lightly scratched crank, albeit with lower oil pressure and shorter bearing life. Presuming the crank is straight and you check/attention the issues in my previous post ie contamination and main cap locations.

[dnegative]

If the crank is marked it needs to be linished or cut professionally, none of this stick it in a vice and get some emery tape shit lol

[wiso]

***Solution***

Ok. I thought I would update this post with a definitive finding on what is causing the low oil pressure that comes up after driving it for some time.

As I described In the first post oil pressure would start off great when cold. Would hold well for a short whle once warm but would then begin to drop to dangerous levels. I was seeing about 14psi at warm but at times would drop to about 5psi or less at idle.

My issue turned out to be the crankcase breather. When running for a long period the crankcase pressure began to build up this began to force down the oil pressure. I discovered this when I opened the oil cap to see if oil was at the cams then happened to glance at the oil guage and noticed the pressure had gone up. Few more experiments confirmed the crankcase breather is blocked in my manifold.

By accident I found this after I rebuilt my third motor because every body on the internet would say its bearing clearances, oil pump etc as they all have here. The first engine was run low for too long trying to work it out and the bearings suffered. The second crank replacement had the same issues. So I then went to an engine builder, Paid a shit load of money and got it back with yet the same issue.

[jondee86]

Not the old... FWD throttle body on the RWD manifold trick ??

Cheers... jondee86

[knightrous]

You must spread some Reputation around before giving it to wiso again.

Would have repped, but forum is being an ass...

[Trivial]

... How can a blocked crankcase breather drop oil pressure?

Wiso - I'm having the exact same symptoms you described, with similar pain to go along with it (Crank has been out twice since rebuild). Recently installed a new genuine pump, ground crank, and new bearings, and I'm having the same issues. Hot idle, it's sitting anywhere from 4psi to 7psi.

I dont understand what 'good' oil pressure is on these engines. The engine shop that did my crank advised me that I should be sitting on no less than 30psi at warm idle? Yet the FSM specifies ~4.3?

[wiso]

From reading many many forum post on this while the bgb says min pressure is 4.3psi at idle I do believe this is far to low. My first set of bearing pictured about always ran about the 4psi mark and a couple of times dropped to about 3psi.

What I gatherer most stock engines seem to run about 15psi at idle and up around the 45-50psi at about 3000rpm. (Generally seems to be the idle psi + 10psi for each 1000rpm).

The easiest way to check if its your crankcase pressure causing low is to pop the oil cap while the engine is running. If the oil pressure goes up the it maybe your issue also.

That said even with my good proper rebuild with 15w oils my oil pressure is about 11psi but when I use 20w oil mine is about 24psi at idle.

I am using 20w-50 now as when I am running the engine hard the 15w-40 oil dropped a further 5psi due to it getting too hot.

[Trivial]

From reading many many forum post on this while the bgb says min pressure is 4.3psi at idle I do believe this is far to low. My first set of bearing pictured about always ran about the 4psi mark and a couple of times dropped to about 3psi.

What I gatherer most stock engines seem to run about 15psi at idle and up around the 45-50psi at about 3000rpm. (Generally seems to be the idle psi + 10psi for each 1000rpm).

The easiest way to check if its your crankcase pressure causing low is to pop the oil cap while the engine is running. If the oil pressure goes up the it maybe your issue also.

That said even with my good proper rebuild with 15w oils my oil pressure is about 11psi but when I use 20w oil mine is about 24psi at idle.

I am using 20w-50 now as when I am running the engine hard the 15w-40 oil dropped a further 5psi due to it getting too hot.

Interesting. After reading your post on taking the oil cap off, I tried mine, and it didnt work. My breather seems perfectly clear.

I am using 10-40 at the moment. I find it insane that 'oil too thin' can be a reason for low oil pressure on a fully rebuilt motor... In your research, are there any other causes mentioned online that can cause these oil pressure 'drops' when warm? (I will start the car at 60psi idle, and it will drop to 40, 30, 20, 10, ~5psi as it warms up)

Edit: That said, I plan on using some thicker oil this coming week. Not interested in sacrificing another set of bearings for no reason.

[wiso]

Try a thicker oil. You have to remember a rebuilt motor will have differant clearances to factory. I am sure they are still within spec but if larger than what your original clearences were then the oil pressure will change. It seems very very common on the forums that rebuilt motors have lower oil pressure than original motors.

Did your engine builder tell you to use 10w-40? Mine told me to use the 15w-40 and my bearing clearences were all between 2.3 - 2.7 thou. So unless yours are tighter than that you maybe using too thin of an oil.

I dunno man. Its something to try maybe. Can't help beyond that

[Trivial]

Try a thicker oil. You have to remember a rebuilt motor will have differant clearances to factory. I am sure they are still within spec but if larger than what your original clearences were then the oil pressure will change. It seems very very common on the forums that rebuilt motors have lower oil pressure than original motors.

Did your engine builder tell you to use 10w-40? Mine told me to use the 15w-40 and my bearing clearences were all between 2.3 - 2.7 thou. So unless yours are tighter than that you maybe using too thin of an oil.

I dunno man. Its something to try maybe. Can't help beyond that

mmm I suppose. My bottom end clearances are all <2 thou, but we will see if the thicker oil helps. Failing that, I am ready to start pulling the head off and making sure I havent messed up the head gasket somehow.

Thanks very much for the assistance mate. Fingers crossed.

PS: Your issue is now completely resolved, and you're riding happy?

[allencr]

... How can a blocked crankcase breather drop oil pressure?

X2? 10 charactersBS

[wiso]

Honestly. I can only speculate. But think about it, massive massive air pressure is buidling up (it might have been vaccum I can't remember now) inside the oil system. Where is that air going to go if it can't escape?

But if your calling me a liar you are more than welcome to try blocking the cam cover breathers on your engine run it with a pressure guage and see what happens.

Yes. Since this issue was sorted and I switched to 20w-50 oil I have been running happy as larry has about 4000km on it now and is going from strenght to strength

[Trivial]

Honestly. I can only speculate. But think about it, massive massive air pressure is buidling up (it might have been vaccum I can't remember now) inside the oil system. Where is that air going to go if it can't escape?

But if your calling me a liar you are more than welcome to try blocking the cam cover breathers on your engine run it with a pressure guage and see what happens.

Yes. Since this issue was sorted and I switched to 20w-50 oil I have been running happy as larry has about 4000km on it now and is going from strenght to strength

Normally if the breather is blocked, the crankcase pressure will build and you will more than likely get oil leaks, rather than a drop in oil pressure. Blocking/unblocking mine has absolutely no effect.

Not calling you a liar - the fact that you were able to resolve your issues by checking the breather is a good thing for you! If it works, it works - I just wouldnt have the slightest idea how.

[allencr]

Been waiting a month for anyone to question a really WAG speculation.
Something is happening, it just isn't the pressure you observed, even if it had been enough to pop front & rear main seals and shoot the dipstick through the bonnet.
Gearotor pumps aren't helped as much as other designs by input pressure, but with any extra crankcase pressure it's still almost a zero-sum-gain, the output pressure isn't reduced because of its surroundings since its input has the same pressure acting on it.

[dnegative]

I cant think of any reasons why a fixed displacement pump wouldn't flow oil in a pressurized environment but when its finger on the PCV valve = low oil pressure and finger off = high oil pressure there has to be something going on?

From what Joel was saying, its seems easily replicated