Need Urgent Help After Rebuild!

[Alex Kraczek]

Where do I start..
Long story short, I just freshened up my shortblock (stock 302 bottom end, std std bearings and stock bore. Block was honed, and crank was polished.)

I started it up yesterday and drove it around. I have a hot idle oil pressure of 22-28 psi, with a mellings pump. My concern is, the oil pressure stops rising past 4000 rpms or so. Cant get it to go past 40 hot, even with 20w50 (hot here in Florida)
I torqued everything correctly, no junk in pump/screen, etc. I have great idle/ midrange oil pressure, just wont rise at WOT. what can cause this? I really dont want to hurt the motor, it runs great and doesnt make any out of the ordinary noises (rockers tick just a tad under light throttle at lower rpms)

Any help would be appreciated, I would really like comfirmation if this is a big issue or not. It is a daily/ occasional strip car. Will be seeing 6k+rpms.

 

[rbohm]

do you have a real oil pressure gauge, or one of those fake ones that looks like a real gauge, but is really an idiot light in disguise? i say first put a mechanical gauge on the engine, and see what you get, and go from there.

 

[MustangIIMatt]

Have you verified that the gauge is functioning correctly? I'd either hit one of the parts stores for a cheapie oil pressure gauge to verify what your current gauge is telling you, or harbor freight (or any other place that sells tools) can sell you something like this: Engine Oil Pressure Test Kit so that you can verify what your gauge is telling you.

Even new gauges can be bad. My less than a year old temp gauge in my II reads incorrectly (haven't changed it out yet, temp readout on the MSD Atomic handheld is accurate, so I'm using that until I get the time to put a new gauge in), I spent a few days chasing an overheating problem that didn't actually exist.

 

[Alex Kraczek]

Im sorry i forgot to clarify. I tested this witg two different mechanical gauges. Same thing. Oil pressure will rise to around 50 cold.

 

[BMW Rider]

New oil pump or did you reuse the old one?

At any rate, that's not terrible pressures, could be a bit higher, but should run fine for daily driving but might be a bit low for the hard runs on the strip. It could also be that after polishing the crank the bearing clearances are towards the high end of specs. Were the rods and main bores resized? A journal at the low end of spec and a bore to the larger limit will make for excess clearance. You might need to consider a high volume pump if so.

 

[Alex Kraczek]

Thanks for the response. It is a semi new mellings standard volume oil pump. The machinist DID tell me that the clearances were on the minimum side, but still tolerable for standard bearings.

 

[FoxMustangLvr]

Not sure those are terrible oil pressure readings. My mechanical gauge reads about 60 during cold starts then gets down to 20-25 for low rpm cruising at operating temp. I haven't looked at my oil pressure when I get the rpms up because my eyes are typically on the road, not my dash.

Also, why 20w50? The heaviest I run is 10w30. I'd be curious what your pressure would look like with a 5w30 or 10w30.

 

[Alex Kraczek]

Funny you asked that, i was actually running 5w30 to break the motor in (yesterday) and thats why i switched to 20w50. I was seeing about the same at hot idle, but couldnt get the oil pressure past 32-36 hot at wot. That scared me. The thicker oil brought my wot pressure up 10psi.

 

[jrichker]

Rule of thumb is 10 PSI per 1000 RPM. For example, at 4000 RPM you should see a minimum of 40 PSI.

Probable causes of lower than normal oil pressure.
1.) Oil quantity too low or too high. Low means the pump won't get enough oil to maintain pressure. Too high and the crankshaft whips the oil into a froth and the pump does not get sufficient liquid oil to maintain pressure.
2.) Clogged or obstructed oil pickup screen.
3.) Excessive clearances between crank and mains, worn rod or camshaft bearings.
4.) Oil pump pressure relief valve malfunctioning
5.) Oil pump to block gasket damaged or missing.

 

[Alex Kraczek]

Um......is that pump to block gasket critical? The old one was ruined, i used some rtv and tightened it down....could this be the problem?

 

[jrichker]

Um......is that pump to block gasket critical? The old one was ruined, i used some rtv and tightened it down....could this be the problem?

Possibly yes.
If both surfaces weren't squeaky clean, the RTV wouldn't stay put to make a good seal.

 

[Alex Kraczek]

I will drop the pan in a couple weeks and put a gasket in there. Hope thats it!

 

[FoxMustangLvr]

Hopefully chunks of the RTV didn't break apart and clog up any oil jackets

 

[Alex Kraczek]

I used a very thin film, so hopefully thats a doubtful scenario.....

 

[RangerJoe]

There was a thread on Corral a month or so ago regarding oil pressure. Several of the engine builders on there agreed that 10 psi per 1000 is actually not needed. They noted that years of testing in Nascar showed that they could actually run closer to 5 psi per 1000. Although, I think the gasket and looser clearances could be to blame in your case.

Joe

 

[mikestang63]

what are your bearing tolerances for your mains and rods? Did you line hone the block? Agreed you probably have some leakage at the pump to block area. Take the dristributor out, take a long 1/4 inch socket and tape it to a long extension attached to a drill and then engage the oil pump shaft and run it in reverse with the car off. see what oil pressure readings you get. That will help isolate if it is the pump or not.

 

[Alex Kraczek]

My machinist is going to send me the specs tonight. No line hone. Same pistons and crank, just polished and bore hone eith new rings and bearings. I pulled it out originally because it was making a horrible knocking noise, and came to find out it was actually a flat lifter (or the bearings, they were all wiped. No spun ones though)
. Anyways, i will have to try that when i get home. What exactly will this test show me?

 

[mikestang63]

My machinist is going to send me the specs tonight. No line hone. Same pistons and crank, just polished and bore hone eith new rings and bearings. I pulled it out originally because it was making a horrible knocking noise, and came to find out it was actually a flat lifter (or the bearings, they were all wiped. No spun ones though)
. Anyways, i will have to try that when i get home. What exactly will this test show me?

if they didnt line hone the mains then eveything might not be square. Think about that crank running for 25 years at thousands of rpms in a 2 bolts main block. You think everything is still aligned? Taht alone will lead to bad oil pressure. Also depending on the brearing clearances, that will impact the oil pressure. If the bearings were not fitted properly or torqued right, again oil pressure can be impacted. Plus about 100 other things .

The spinning of the oil pump shaft will tell you if the problem is with the oil pump. The motor wont be turning. If the oil pressure wont build or jumps around when you are spinning it with the drill, you've isolated the problem. make sense?

 

[sharp2377]

those numbers arent bad. especially if you tolerances were at the minimum. its fine, but you should have put a gasket between the oil pump and block.

 

[Alex Kraczek]

Thanks alot for the input guys. I performed the pump test with car off. Hot oil- 42 psi. I could not get it to go over that. I pulled the pan down, made sure the mating surface was clean, and put a gasket in there. Primed it, got it to 55psi (cold). My pressures havent changed a bit since the gasket install. Im just going to let it ride. Any other input guys?
Thanks