Not very often I make a post for help, but I'm effectively stumped on this one.

A little background first.

Motor in question is a 70's 307 in a boat. Not believed to have a hi-volume pump as the motor has never been rebuilt and only has 375 hrs on it.

Oil pressure is rock steady at idle and up to about 2000/2500, but when you run the throttle down and run it up to 3500-4000 for any period of time, after 10-15 seconds oil pressure flutters and drops steadily until you back out of it. After you drop the throttle back to idle, oil pressure comes back within just a couple seconds.

What I've done so far.

I've pulled both valve covers and checked the drain holes in the head for blockage. No dice. They're clear and they drain like they should. The pan has been pulled and the pickup checked out ok. No blockage or anything else out of place at all. The motor has been meticulously maintained and is ridiculously clean inside and out. I've changed the oil to rotella thinking the previous oil was foaming and noticed no change in performance. I've even tried over oiling it by a full quart with no change.

So, in a nutshell, I'm almost convinced the pump is emptying the pan, and it's not draining back fast enough. However, I have asked several "folks in the know" and got the same response. "That motor shouldn't have a hi-volume pump in it."

What say ye PBB?

you might check the distance from the bottom of the pan to the pickup tube.

if its too close it might suck the bottom of the pan up to the pickup.

Shit.

Forgot to mention, used memory foam instead of light clay and checked it to 7/16".

Too close? No?

If i had any hair, I'd be tearing it out soon...........

might be too far.

distance should be 3/16"

ever think the pump is just worn out, at the slower speed the pump is holding it prime just fine and when you start to spin it up in the higher rpm range it starts to lose it ability to move oil. i have seen it on mechanical fuel pump on desiels and in water pumps never seen it in an oil pump.

did you try puttin a thinker oil in it like straight 50, i know in a lot of older cars have kinda the same problem, they are not used to the new oils and when they get hot they lose oil preasure, if you put in a thinker oil they run fine and dont have any problems. just a few ideas.

The original owner always ran 10w/30 in it.

I tried the rotella 15w/40 with no change.

I had thought about non-detergent 30w, but was kind of apprehensive due to the amount of sludge that shit makes.

I'm not opposed to running some much heavier oil, but what effect would that have on the distributor shaft and the plastic sleeve? I've run 20w/50 in my wheeler for a few years now, but never played with straight 50w. Never had to cover up a problem that big.

Grumpy, your thoughts on this?

I have some small (5/16") solid round stock in the garage. Maybe weld two small slugs @ 3/16" long on the lowest point of the pickup rim to keep it at a constant seperation?

Hey Capn,

In a Marine application the 307 would have a cast pan ,and much less prone to any change in sump to pan clearance.

What are Your actual Oil pressure #'s, is this condition under load or static?

Are You still running original mech gauge?

Are these motors Chris's on Paragon's? (heavily baffeld oil pans)

Kiwi

edit: If You'd like to rule out sump oil starvation..check oil on stick while pressure is down, if stick is not long enough,.. make coat hanger dipstick to make sure You hit bottom of pan, Easy first.

Wow.
Maybe the internal bypass spring is weak. When oil is cold and thick, the pump has the ability to split filters from excessive pressure. So pressure is bleed off by bypassing the filter.
Its located in the filter adapter, the part the filter threads on to in the block.
Best way to disable it is to remove the spring and disc valve, tap the hole with a 1/4 pipe tap , and install a 1/4 pipe plug.
The spring could be fluttering.
???

you might check the distance from the bottom of the pan to the pickup tube.

if its too close it might suck the bottom of the pan up to the pickup.

Finally!!!! some words with value to the thread from this guy!!!!!!!!!!!

Finally!!!! some words with value to the thread from this guy!!!!!!!!!!!
so, with your 2 posts, what words of wisdom do you have to offer? what kind of info could you impart to the masses that might be of import? Do you think that the crank might be somehow bleeding all this oil pressure off before it reaches the sending unit? perhaps the cam galley bleeds pressure by the freeze plugs at the front of the block at high rpm?

maybe some other version of bullshit, but you dont post any tech, do you?

go fuck with someone else, kid. you wont like the result of fucking with me.

KIWI...........

Pan is sheetmetal, and we already pulled the guage and checked it for proper operation on another vehicle. It's electric also, with a borg-warner sending unit.

Grumpy............

Fuck that idiot, he's obviously "that guy" that changed his own oil and now knows more about engines than Bill Jenkins.

Anyway, I'm wondering if the bypass spring mentioned earlier is the culprit. Haven't covered that base yet. Also, is there a possibility that I can get an entire bypass housing from another motor, say maybe a truck engine that would have a heavier spring? Or am i shootin in the dark with that one?

to boost pressure, all you need is one holley jet.

remove the spring, insert the jet into the end of the spring and reinstall.

does it clatter.if it doesn't tick i would install a mech guage to confirm the pressure is actualy dropping and not a faulty sender.

Sorry, I forgot to include that the sender was a NEW borg warner unit. I've checked senders and guages in various combinations in three different engines and the condition doesn't change.

I'm going to attack the bypass valve tonight and see what she does.

If you're going to eliminate the bypass in the adapter you might as well eliminate the bypass in the filter at the same time. Wix p/n 51061R would do it for you.

so, with your 2 posts, what words of wisdom do you have to offer? what kind of info could you impart to the masses that might be of import? Do you think that the crank might be somehow bleeding all this oil pressure off before it reaches the sending unit? perhaps the cam galley bleeds pressure by the freeze plugs at the front of the block at high rpm?

maybe some other version of bullshit, but you dont post any tech, do you?

go fuck with someone else, kid. you wont like the result of fucking with me.
dude cleb status... somone snaking your name sort of haha. thats actually kindof funny

I've never seen a Marine 307, without a cast oilpan.....and I've seen a few.

Possibly an auto replacement for a freeze cracked original?

When You talk about Borg Warner parts, I take it this is motor is driving a VelvetDrive.

Kiwi

if your taking it all apart why dont you just go pick up a new pump and see what happens. your in there already