Oil pressure flutter at higher rpms.
 

So, I've never gotten this engine over 5k rpms due to crappy carb jetting but now the bugger can spin up to 5400 and occasionally 5600 and I'm seeing a bit of pressure flutter above 5k. It's not much but the needle is definitely twitching but is solid at rpms lower that 5k. Is a problem developing?

502 with less than 100 hours on it. ~500hp
Brad Penn 10-40. 70psi cold 60psi hot. It'll drop down to about 25psi at idle after a hard run but quickly recover to 35.
Stock GM 6qt pan
Oil level a little high because I've been fighting a small leak at the filter head. Possibly a quart high.
3x18" oil cooler with -12 lines. No thermostat currently.
Compression check shows 180-185 with the #1 a little weak at 175#

Two possibilities I'm seeing:

1) The over fill is causing the oil to get whipped up by the crank foaming it up.

2) The oil pan is on the verge of getting sucked dry with oil pooling up top on the motor and it cant drain back as quick as the pump sucks it out.

Make sure sender connection is tight. Similar issue happened to me.

There's a possibility there as I was fussing in that area sorting out the stupid leak.

im with trash on theory # 2.

Time to take a long drill bit through the heads and block into the pan? Need a bigger pan?



*J/k on the drill bit.

10w-40 ?

Is the block screened? Of so I woukd say the pan is running dry, if not it should be ok but very close to running dry, I was in a situation that I had 6qt pans and ran 5500 for a long time never had issues... But all boats and systems different

Yah. That's what it came back from the machine shop with so I just stuck with it. Seems thin for marine use, but I don't have a thermostat on the oil cooler yet, and rarely get near wot on our small lake, so I figured thinner is fine for now.


By "Is the block screened?" Do you mean in the pan or up in the heads? All of the orifices in the top end are open.

Another vote for sacking pan dry.

Try adding a quart of oil to see if pressure is steady. If so you need bigger pan.

Overfilling the pan is bad.

What size oil lines do you have to and from the filter? Icdedppl recently solved his oil psi issues at high rpm after fighting with it for a few years now. The culprit, -10 AN lines . He replaced with -12 lines, and oil psi no longer drops at higher rpm.

The valley of the block, sometimes a screen can limit how fast oil comes back to the pan

Everything oil related are -12 lines and 3/4" npt. I've had trouble getting the new Hardin remote filter head to quit leaking and have been changing fittings, and I had to bend one hose (from filter head out to cooler) with a slight bend in it. Not a kink, but enough to slightly deform the shape of the hose a bit. It didn't look like much of a hinderence though. This is a new development though and that's the only change made since the last time out when it was fine.

Before I'd get to excited plumb in a mechanical gauge and temp line up to or near dash to confirm just to make sure you get the same readings.

Btw you using same carb you were and just jetting and PV change or did you purchase new carb.

Same carb. Changed the PVs to 4.5 and got 11.8 across the board. Dropping the primaries from 78 to 74.

I guess that I'll switch out that tight hose, check the sender wire, and go from there.

Definately deal with that hose !

And if it stays tight longer than 4 hrs, you should see a doctor !

Gonna hafta use my pimp hand to deal with that ho...

I doubt its the hose or fittings, my old engines 565CI and 600 hp, had the factory brass sharp 90's still and also 6qt pans, never had an issue, I held them at 5500 for miles at a time never sucked pan dry, I am sure I was close but at the time I had what I had.... blocks did not have screens limiting oil return either, so if you have screens that can hurt maybe, or look at other things.... start with a mech gauge and verify for sure then move on, until then it could be a stupid sender or gauge issue..

A tight line still needs to be replaced. IMHO.

I agree as always checking with mechanical gauge.

I would also adjust oil level to proper height.

all good replies and will add just for the heck of it. Wires on the back of the oil pressure gauge tight and clean with good connections, also a sender that is over tighten can cause problem readings as well. Also no Teflon tape on the sender correct ? Wire connection on the sender and no corrosion on it either. Rusted up sender and or connection can cause reading issues Just posting on top of. Seems like everyone else covered it all.

You must have looked like a diesel from behind if you messed with the carb as stated in original thread and picked up near 600 rpm. Dam bro... 5k to 5,600 after jetting. :eekdrop:

Disclaimer: I am a hack, in particular with boats, and especially with carburetors as I can get impatient so my control experiments can be a bit loose, vague, and inaccurate. But yea, there's a lot of soot on the transom with a few complaints of the fuel odor tainting the lunchtime wine pairing, lol.

Also, my gauges are pretty crappy twenty year old Baja OEM stuff, so I barely trust them for any accuracies. But the jetting change literally transformed the behavior of the boat just from going down a couple numbers on a set of jets. These are the first tangible results that I've gotten to get the boat performing anywhere near where it should and I'm stoked.