BBC Oil Pressure Issue

[cyclone]

My BBC shows 70psi of oil pressure when cruising at 4,000rpm. If I floor it, the pressure will drop all the way down to 20psi by the time the motor spins 5,000rpm. According to the gps, the boat is still building speed, but i have to let off the gas because of the drop in oil pressure. If i ease into it, the pressure will hold at 60spi. Its almost like the oil pump is cavatiting. i have a 10-quart pan on the motor, but i dont know if its got a trap door or windage tray. Any suggestions? I was considering going to a thinner oil.

[Clown]

Cyclone!
I've had that same problem when I used Royal purple Oil Racing#9 weight. It did make 10 more HP on the dyno but I would not recomend it to be used in a pleasure boat!!!The 6th pass I had that problem with it not wanting to build oil pressure When it was up to temp.So I would not recomend a thinner oil!
My problem was that I started to wipe out a couple of main bearings.
Now I'm just an a$$hole !!!!!!!????
So dont listen to me I'm just saying that I had almost that same problem.
???Maybe your pump pick up is cavatiting when you excelerate hard,It might just be in the wrong location and not the pick up or the pump at all! eek! I'll start smokin my crack pipe now eek!
And see if any of my buds have run into that same :confused: Problem!!

[cyclone]

ok so dont go thinner with the oil then? i'm all out of crack.

[Clown]

Right
If anything go with the mercury racing oil I think its 15w40 but not exactly sure on that number its been awhile since I've run that stuff.
It is good stuff dont get me wrong!

[cyclone]

i wonder if this is just an oil weight problem or if there is something else going on?

[comin' unscrewed]

Is this a new motor, or did the problem just develop?
If it's new - did you check the clearence between the oil pickup and the bottom of the pan?
New or not - I've had the plunger in the pressure relief get sticky on a couple of motors. They did EXACTLY what you descibe. I had to pull the pump and then I applied a little valve lapping compound to the plunger and spun it with a hand drill. Solved the problem both times.
By the way, one of these was brand new pump.

[cyclone]

I just bought the boat and the owner says that the motor had only and hour on it.

[Clown]

Also their is a bypass built into most oil filters!

[Rexone]

If it's new - did you check the clearence between the oil pickup and the bottom of the pan?
New or not - I've had the plunger in the pressure relief get sticky on a couple of motors. They did EXACTLY what you descibe. I had to pull the pump and then I applied a little valve lapping compound to the plunger and spun it with a hand drill. Solved the problem both times.
By the way, one of these was brand new pump.
I agree, we've seen both these problems and they can cause what you are describing

[Clown]

Rex one I'm in the process of building a 496BBC with twin turbo's . Please E:Mail me If I can twist your Brain a little :D

[cyclone]

so what you're saying is that essentially i need to pull the motor, pull the pan, and check the clearance between the pickup and pan?

[carreraboat]

sounds like you also may have too much oil in it if you have tooo much you willl foam and the presure will drop off

[HM]

cyclone:
I just bought the boat and the owner says that the motor had only and hour on it.and driven by a little old lady on Sundays only. :D

[flat broke]

Mike,
Where are you taking your oil pressure reading from? Right at the boss above the oil filter? if so, plug that hole and move the sender as far forward on the motor as possible. If you're having bypass problems, its harder to see them with the sender in the location above the filter because you almost always have pressure there. If you move your sender to one of the gallery access holes up towards the front, you might get different readings that would shed more light on your condition. I'm definitely not saying that moving the sender is going to fix your problem, but it very well might allow you to get a better view of your oiling systems performance throughout the motor.
Now to guesses on the pressure issue itself. Since the motor was only 1 hour old when you came into possesion, does the guy have receipts from the rebuild? If so, look for a new oil pump in there. Also look and see if there was any labor to fit/blueprint/rework the pump. I know George at Clay Smith takes a lot of time when setting up the oil pump for your motor. Even brand new pumps are torn apart, a quality pickup is brazed into place, then the pump is setup with new gears, flowed etc. If the guess earlier in the thread about cavitation is correct, you might try sssslllloooooowwwwwlllllyyyyy increasing the RPM to see if you maintain your oil pressure. Outside of cavitation, do you have an oil temp gauge? They provide vast insight into oil pressure problems as you can rule out excessive heat and move on to the next possibility. It could be that your new motor was set up a little tight and for one reason or another you're seeing higher oil temps than others. This would cause the pressure to drop QUICK. When you run the motor to 5k, loose pressure and slow back down, can you cruise again after a minute or so and get a 70psi reading again, or is it once the pressure drops thats pretty much it? If the later is the case, I'd definitely look towards oil temp. As far as going to thinner oil, as stated, that's only going to make things worse. Ty and I run Valvoline VR1 straight 50 at the recommendation of George, and it works well. I've also heard of running an oil stabilizer to keep the oil from breaking down at higher temps but don't have any solid info on that.
Good luck with your ride, and if you need any help, feel free to give me a jingle. BTW, we're heading somewhere for booze and food on Saturday night so feel free to join us. Hopefully RR and HB will be able to join us as well.
Talk to you later,
Chris

[cyclone]

Chris- if i let off the gas, the oil pressure comes right back up to 70psi immediately. if i ease into it, it will maintain pressure, its only when i stomp on the pedal that the oil pressure drops. It does this whether i've barely warmed up the motor or been running for 10 minutes. I'll have to check into the sending unit location. thanks!

[flat broke]

Deffinitely sounds like cavitation in the oil pump. Since you're running an BBC, the pickup should be in the back and thus oil slosh should not be a problem (unless somone mistakenly installed a V-drive pan and pickup which would have moved your pickup to the front fo the motor where it would be a potential victim of oil slosh in the pan). I'd start looking at the pump itself. Give George at Clay Smith a call and see what he has to say about your situation. He's a good guy and definitley knows his s**t. Better yet, stop by Clay Smith in person as your odds of catching up with him might be better that way. Their number is 714-523-0530 and the address is 5870 Dale St.
Buena Park, CA 90621
Good luck,
Chris

[cyclone]

thanks chris!

[Rexone]

Clown, no problem, just PM me any questions you have and I'll do my best to answer them.