i suppose... but for me this all sounds like some really basic configuration problem. the combination is too ordinary and understressed for this to require some space alien solution.

i mean, really... this combo with factory clearences , a box stock oil pump, a box stock oil pan and off the shelf oil at 220 degrees and the correct relief valve put in the right place. should run at 25 psi idle and 55 to 65 at speed essentially trouble free forever. it gets done exery day and twice on sundays ( as they say ) ... so whats different here ?

Had same issue on my motor a couple years ago. Nobody wants to take out a quart of oil, but i tried it and problem solved. Windage was the issue for me.

Just to clarify my motors havn't ever blown up, I think the original poster"s did and were rebuilt. I'm not trying to hi-jack the thread it just seems like we both have the same problem. Sorry for the confusion. I have temp gauges on mine and I never see anything over 190 for oil temp so i know it's not heat. Star motor never drops below 50psi at 5200 and port will drop to 35-38 psi at same rpm. If I back down to idle they will both drop to 20 psi and work back up to 50psi after about 5 minutes. Both motors obviously have the same parts so oil pan size or oil line size or fittings can't be the issue. Problem motor also burns a quart of oil after running a couple hours and other motor burns none. I know somethings going on with this motor just don't know how serious it is. They both run perfect. I just keep adding a quart of oil and hope to make it through our short summer up here. Thanks for all the help. Jason

X2

And I would also run at least a straight 40w oil or 20w-50. Even stock Merc oil is 25w-40.

I like your analogy, re-read this thread however, there are 2 different people posting with oil pressure problems, I completely agree that a STOCK motor with STOCK clearances will be o/k with the STOCK oiling system as long as everything is right and the right amount of oil and correct visosity is used. But back to the modified questions, yes, it is possible that the guy asking the questions has too much oil in his motor BUT the info I have posted and my own personal experience is the solution to ALOT of the oil pressure problems that come up on this board every year tiome and time again. I know you feel Mercruisers oil system is sufficient and it is until you start changing everything else. The typical problem on here is a guy takes a motor and builds it with "performance" clearences, goes from .0015 or so rod clearence and .001 main clearence to .003-.0035 rod and .0025-.003 main in turn the oil supply requirements of the motor are effectively doubled, it is common fact that with stock clearences a bbc needs about 4-5.5 gpm of oil flow to "float "the bearings and hold reasonable oil pressure. As soon as you increase this it obviously goes up in proportion and the common number is more like 8 gpm. Right or wrong the typical shop puts crank clearences up to the higher numbers I quoted earlier, guys uses a high volume oil pump with the idea it will keep up but the stock cooler, fittings and hoses are used caussing a restriction, as I have shown in previous threads the stock id of some of this stuff is as small as .375. Picture you have a 60 psi water main, you buy a 5/8's inch garden hose, you put a sprinkler on the end and yes, you have a nice shower of water spraying from the lawn sprinkler, if you were measuring static pressure you would probably have 50 psi at your hose. Now, picture trying to run (2) sprinklers on one hose, damn, the water only sprays out a few feet instead of having a nice pattern and static pressure is only 25 psi, a bbc with higher than stock clearences is no different. You buy a one inch hose and put in a 1" supply line and valve and presto, it sparys good again.
As far as viscosity, I have tried to run lower vis straight weight oils before, never worked great hot unless crank clearances were near stock, had azz loads of cold pressure though. I broke my motor in on the dyno last time using a lower weight oil as it holds so much it never gets ll that warm and thin on dyno pulls, I had crazy high pressure after switching from a Merlin block to a dart block. I had extra medium weight oil left over and refilled the motor with it for its final break-in in the boat. As I made a long cruise down the St Claire river the oil got quite hot and subsequently thin, I would be cruising at 3800 and had 65 psi, I would tip into the throttle and as rpm's went up oil pressure would proportionately drop, made me quite nervous, I couldn't get back to my shop fast enough to cut my filter open and see if I had screwed up. Nothing in the filter I put my normal heavier oil in the motor and I have put 80 problem free hours on it since, so I have personally seen this, Smitty

A old thread where I describe the problem I had with oil pressure DROPPING under throttle just so you know I'm not making this **** up, I currently run 20/50 synthetic,Smitty
http://www.offshoreonly.com/forums/g...-pressure.html
Originally Posted by 88Fount33 View Post
I build my 540, at first tried 20W50 and had 80 to 100 lbs at idle cold, and 80 idle hot, changed to 10W40 syn and now have 80 lbs cold, 60 lbs hot, and about 75-80 wot. It was enough of a drop to make me feel good about not going back into the engine.
I ran into almost the same exact scenario this year,I switched from a merlin 2 block on my 540 to a dart block,assembled motor with .0033-0035 on rods and mains (nothing too tight by any means),used the same part number melling high volume blueprinted pump with high pressure spring and found I had 100 lbs of oil pressure most of the time when running 20w/50 kendall gt-l,I used the same oil, Same part number oil pump,same brand lifters,etc,same crank and rods but crank was polished even looser and enigine has 20 lbs more oil pressure then it ever had before. I ended up running 10w30 synthetic on the dyno after we were sure rings were seated and been running 5w40 synthetic this season to get oil pressure to a normal level. Putting a softer by[pass spring in the pump(which I have never had to do) would just cause the oil to churn and heat up more in the pan. I think I could have used a pump with shorter gears in it. The thinner oil was a good fix BUT I was out running one weekend and the oil was due to be changed (it had about 14 hours on it) and I noticed if I leaned on the throttle above 4000 oil pressure would drop,cut filter open there was nothing in it,changed the oil everything was back to normal. I normally change oil once a month around 10-12 hours (it gets fuel diluted fast from the blower set-up running rich),I think with the thinner oil the oil thinned out faster from fuel dilution so I am just keeping a eye on it. The merlin block must have had more internal leakage then my dart block,I know the lifters were bleeding some oil off because of the short lifter bosses on the merlin block,the dart bosses are longer,Smitty