DrNautica

I have a 540 CI 686 HP NA GM Bowtie Block, Callies Crank, Oliver Billet rods and Dan Olsen oil pan. All of the bearing clearances have been painstakingly set up and are on the tight side of the spectrum. The oil pump has been rubbed on to tighten clearances as well.

My oil pressures? 60psi cold, 50-55psi hot at WOT, and 18-20psi at idle after a hard run. The idle oil pressure will come back to 30psi after a little cool down time. I run dual oil temp sending units to an electric Gaffrig Livorsi gauge through a DPDT switch. One sees oil coming out of the block into the oil thermostat (hottest oil) and the other sees oil coming back into the block from the oil cooler (coolest oil.) I routinely see 250-270 during a hard run on the "hot" sender while seeing only around 180-190 on the cool sender. So I know the oil cooler is taking out anywhere from 60-80 degrees of oil temp. I also run dual oil pressure gauges, one Gaffrig Livorsi electric with the sending unit located in the top rear main galley plug (behind the distributor) and an Auto Meter Pro Comp mechanical gauge with a SS braided -3 line located off a T in the same location as the electrical sender (so they see the same pressure.) The gauge readings are typically within 3-5 psi with the mechanical gauge showing the higher readings.

70-80psi at WOT would be ideal and idle pressure shouldn't be below 30psi. I feel mine is too low. This is my second rebuild on this block but this time we did the new rotating assembly. This rebuild was primarily due to my concern with low oil pressure. Well, it didn't change things any. When I disassembled it the last time, the calico coated bearings (both mains and connecting rods) were in pretty decent shape so I'm convinced that the lower oil pressures in my setup aren't really hurting anything. I actually think that I may have an internal oil passage leak in the block itself.

I will guarantee that windage is NOT an issue in this engine with the Dan Olsen pan which is a 10qt in which I run 8qt.

I am very interested to see what others have to say here.

Dr. N

Wobble

Those were about my numbers when I was running M-1 15-50. The switch to M-1 20-50 will pick up your hot idle and wot pressures noticeably, about 10+ pounds across the board for me.

What oil and filter do you run? I have seen a difference in oil pressure between brands of filters also.

The oil temp cooling efficiency numbers came off a major heat exchanger manufactures web site. I also have two senders, with the Teague Offshore cooler I see about 50* drop which is right in-line with the manufacturers specs.

Wobble

Patrick,

That does not sound right, I assume you have verified these numbers with a mechanical gauge.

What generation block is it now and what generation is your oil filter pad adapter?

Read this thread by Articfriends and you should be able to pinpoint the bottle neck in your system http://www.offshoreonly.com/forums/s...ssure+problems.

26scarab

10 psi per 1000rpms is what I alway's heard also. Unfortunatly in my motors case I don't have anywhere near that. I have a max of 35-36lbs hot at 5800rpms on a mech. gauge. The bearings have always looked fine.
Maybe pressure is a little over rated, volume and keeping the temps down seem more important. I certainly don't like the fact that my pressure is so low but I don't think I can really do anything about it other that replace the crank.

Kind of a different thing but a friends Comp Eliminator car has some crazy really small CI SBC that goes thru the traps at 10,500 rpms with a total of 20lbs of oil pressure with 0 wieght oil . Now I know that is completly different than holding a motor WOT for miles but it does show that pressure isn't everything.
I'm not an engine builder so I could be completly wrong , they are just opinions/observations. That is what is good about this board learing differen't opinions and things like that.

BY U BOY

IT IS A MARK IV BLOCK RETRO FIT TO A ROLLER. THE ONLY THING I LEFT STOCK WAS THE CRANK. BEFORE THE REBUILD I WAS GETTING 60PSI AT IDLE AND 70 AT WOT. I REPLACED THE OIL PUMP WITH THE EXACT SAME MODEL AND DID NOT CHANGE ANY LINES. THE ENGINE IS STILL GETTING BROKEN IN SO I HAVE NOT MADE ANY LONG HARD RUNS AND HAVE ONLY GONE TO 4500RPM FOR A MIN OR TWO. WAITING ON A PROP FROM BBLADES SO I CAN GET TO 5000RPMS. I HAVE CHECKED OIL PRESSURE WITH A MECH GAUGE AND IS THE SAME. MY BUILDER DOES NOT THINK THIS IS A PROBLEM AND SAYS I AM GOOD TO GO.

Wobble

Gen 4 mercruiser motors had the bypass built into the filter pad adapter. If this part was baked during the rebuild process, the spring is no good. This could result in lower oil pressure.

I had mine plugged as it is bltch to get at with the motor in. That way all the oil goes to the filter and no worries about it bypassing.

BY U BOY

I DID NOT KNOW THAT I WILL TRY TO CHECK THAT IF I CAN GET TO IT. DO YOU HAVE ANY PICS OF WHAT YOU DID? I AM ALSO RUNNING A 8QT PAN WITH 9QT IN IT AND AM NOT GETTING ANY FOAM. I HAVE PUT 10 HRS ON IT SO FAR WITH NO PROBLEMS OR NOISES THAT I CAN HEAR AND OIL STILL LOOKS LIKE I HAVE NOT RUN THE ENGINE AT ALL. IF I HAVE TO PULL THE ENGINE AGAIN I AM GOING TO SET THE BOAT ON FIRE

articfriends

I agree with mrhorsepower,my 540 runs 80 psi cold at anything other than a idle,70 psi at wot fully warmed up,idles at 60 psi cold at 700 rpm's and drops to 40 at idle after a long, hard run but comes back up to 45 or so after a few minutes of idling. If you have a good high volume pump and your only seeing 40 or 50 psi at wot either oil is bleeding off thru a excessive clearence somewhere or there is a restriction in the oil plumbing causing oil pressure to bottle neck somewhere or a combination of both.Look at my oil pressure from stock hardware thread for in depth pictures and examples of restrictions.For anyone running any part of a stock 502 merc oiling system with a motor with a high volume oil pump or looser than factory clearences keep in mind every single factory fitting will cause a restriction as they are tiny. I experienced this on my first 502 blower motor,it would run 55-60 psi at wot cold and drop to 40-45 psi. I changed every bit of plumbing from the block out to the return fitting in and GAINED 10-15 psi. Bigger fittings can't create oil pressure but too small of ones can sure restrict it. Another tell talle sign is if you see excessive wear on your cam gear or distributer gear,the teeth will scallop because oil pump is deadheading against the plumbing,literally lifting the bypass valve in the pump constantly because pump is putting out more than fittings can flow,Smitty

26scarab

Smitty,
After reading and rereading this post and your other post about oil systems it hit me. Maybe it isn't the rod side clearance that is the issue like I've thought maybe it's in the oil cooling system.
I know my bearing clearance is .0025" and I'm running a System 1 adjustable oil pump ( 234-900773-2) so if the rod side clearance is okay then there should be no reason for low oil pressure. But what got me thinking it was in the rigging of the new oil cooler cause several of my friends have had motors built buy the same guy and the ones that just used our old 502 accy's and just added oil coolers have the same low oil pressure issues, some are a little higher than other but knowwhere near the 50 and 80 numbers you guys have been seeing. We all can't have screwed up rod side clearances.
I do know when I rigged my new oil lines up I used 1/2" but I know for a fact I used a straight fitting into 90 degree adapters, and I've got the stock 502 filter adapter and stuff. Maybe this is the reason for the low oil pressure.

DORaymond

If you were to remove the remote filter housing and screw the filter directly to the engine, wouldn't that give an indication of how restrictive the cooler, etc. is? I wouldn't run the engine hard this way.