Oil Pressure Behavior
 

Guys,

I've noticed something a bit odd in the oil pressure in our boat and wanted some guidance on how to think about or deal with it.

Merc 496HO, never been opened up, to my knowledge, so stock internals. It has an M1 ProCharger and a stage 2 Whipple tune, if it matters.

I can run around all day long at idle through cruising speed, and oil pressure stays a reliable 40psi, idle through ~3500RPM or so. But as soon as I stab it and run WOT, or close to it, for any significant length of time, and then drop down to an idle, even after some considerable cruising speed running, the oil pressure drops to ~20psi for awhile, then eventually creeps back up to 40psi over the course of about ten minutes of idling. Oil is fresh, Valvoline high zinc 20W50 Racing oil (last late summer), clear and topped off to the top of the service range on the dipstick.

What do the gurus think might be causing this and is it a cause for real alarm?

Thanks. Brad.

what are you using for an oil cooler? i suspect the oil is getting to hot when running it hard,i like to see oil temp in the 200 to 220 degree range.

Sounds Normal
 

As long as you maintain good pressure when running hard your not aerating the oil or it's not draining fast enough back into the pan,,, your good.

Some drop in oil pressure is expected after a hard run. 20lbs is more than enough at idle until it recovers.

Mike,

Whatever came stock with the engine/boat. I don't see anything resembling what I've seen that was called an oil cooler here on OSO. Is there a "stock" one that is integrated into the transom assembly?

Thanks. Brad.

Oil pressure varies
 

It does in cars, too, unless the gauge is faking it.

Follow the lines off the oil filter housing and you'll find it. With the Pro Charger, it really should be updated over the stock piece (which is quite small).

The stock oil cooler on a 496 is on the port side of the engine above the Cool Fuel housing. It's not very big. Might want to install an oil temp gauge and see where you are at after running hard.

Mine was running 'normal' in a 350 (pair) then after a while at cruise (20 min+) it would drop 20PSI. I removed about 1/2 quart, and now it's dead on. I think it was aerating my oil.

Knot,

I found it. It's farqing buried down there. Will definitely look into installing a temp gauge.

Thanks. Brad.

Just wait until you have to replace spark plugs on that side. :eek:

Seems pretty normal for marine engine. Mine will drop to 18psi sometimes .. oil cools and it comes back up with some rpm

stock cooler that was sized just big enough to keep a stock engine at a reasonable temperature. It all cpmes down to hp equals btus/heat/friction. I have had a few customers were we increased their hp from 415 etc to 600 and used stock cooler. The oil quickly heats up, when running it hard, keep your sustained wot to short burst, install a oil temp gauge. Problem is it probably never stabilizes IF you kept it at wot, ie, if you held it for 20 or 30 minutes at wot it would probably blow up eventually where a blower engine properly tuned with big enough cooler will usually be able to hold sustained wot.

Tom,

I'm thinking I will be leaving that to the more adept and compact. :readinghelp:

Thanks. Brad.

Knot,

I've got that part down. did it five times in a matter of a couple weeks when I was trying to root out what turned out to be bad injectors. One is a serious PITA to get to, but, all-in-all, it ain't too bad.

Thanks. Brad.

Smitty,

I rarely run it hard for more than a couple minutes, if that. I'll be looking into splicing in an oil temp gage, though.

Thanks. Brad.

It's good to know that 20 lbs after a hard run is okay.

PQ290,

*At idle....

Thanks. Brad.

Similar story with my 502 MPIs - they’d drop down to 20 or so at idle after a hard run. I’d kick the idle up a little to cool the oil a little quicker. That was with Mobil 1 15/50. When I took it all apart to do the new builds, the bearings looked excellent. They had about 400 hours on them.

I've run multiple build combos of supercharged 496HOs. They need a larger oil cooler. I can't stress this enough. Put an oil temp gauge in. If using the factory oil filter mount I drilled the base and installed the sensor there.

I've done a bunch of experimenting with the oiling systems on the 496HO. I ended up with a 3''x18" oil cooler, -12 lines, and an aftermarket high flow oil filter base in order to keep an 800HP one cool. -10 lines and the factory base worked to keep a 600HP cool using a 2.5" x 19" cooler.

Just a tip: I repurpose the factory engine oil cooler and use it for the power steering cooler, this frees up the rear of the engine for a larger engine oil cooler without doing too much modification to the factory water routing!

Be careful with your temps!

Right on. The stock cooler is adequate for a "stock" engine. Oil temp gauge is your friend.