Erratic oil pressure above 4300RPM
07-06-2010 | 10:55 PM
#1
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From: Whitefish Chain - Crosslake, MN
Erratic oil pressure above 4300RPM
OK, here's the deal. I got my 383 back in the boat after a re-ring and I decided to put a custom cold air intake on it and plumb it to the vents on the back of my boat below the sundeck of my Stingray.
Today the wife and I go out for a cruise and after a run across the lake we run through a channel; take off and the motor starts to stumble. Back off and pop the engine cover only to see water in my clear breather lines. Realizing I have water in my intake ducting, I pull off the 90 degree elbow that attach to the back vents. A significant amount of water poured out of both and there did seem to be moisture coming out of the breathers. Checked the oil level and it was right where if was the day before when I added oil so there doesn't seem to be too much moisture.
Engine starts out having about 70 lbs of pressure at just above idle and drops to 60 when warm. Get back on plane and running 3000RPM all fine, kick it down a little bit and get above 4300 and the oil pressure gauge gets erratic. Drops to 40 and will blip down to 0-10 if I stay into it, but I back off pretty quick. I have not yet hook up the low oil pressure buzzer, but would water in the oil cause the pressure to get erratic above a certain RPM (pretty consistent what RPM it happens at)? I'm running a Melling Select std/std oil pump with a bolt on 3/4 pickup. Pickup is 3/8” from the bottom of the 7qt w/filter pan. Running with no bypass into a remote oil filter (Napa Gold) through -10 Push-Lok hose then into a 2x18 oil cooler, then back into the remote adapter. Pressure sending unit in mounted above the oil filter pad and the disconnected low pressure switch is mounted in the oil filter mount. Break-in oil is Rotella T 15w40 dino.
1) I have a factory roller cam motor with the dog bone retainers. Could I loose oil pressure like this if I popped a lifter?
2) Is my sending unit goofy, this oil pressure fluctuation did not happen the day before? If there was an electrical problem, I would expect the other electric gauges to be erratic.
3) I’m planning on pulling the valve covers tomorrow to check the rocker adjustment (to check for popped lifter)
4) Does the low oil pressure buzzer come on right when the pressure drops below a certain level, or is there a time delay (what pressure)?
5) I have an oil sucker that I can stick down the dipstick tube to see if there is any water sitting on the bottom of the pan, but the oil is not milky. Will more than likely just change it.
I do not have a mechanical gauge on had at the cabin (on vacation), but I’m pretty sure the local merc dealer has the sending unit on tap. Is it just a standard chevy oil pressure sender?
Any suggestion, questions, feedback, or guidance on what I should do.
Today the wife and I go out for a cruise and after a run across the lake we run through a channel; take off and the motor starts to stumble. Back off and pop the engine cover only to see water in my clear breather lines. Realizing I have water in my intake ducting, I pull off the 90 degree elbow that attach to the back vents. A significant amount of water poured out of both and there did seem to be moisture coming out of the breathers. Checked the oil level and it was right where if was the day before when I added oil so there doesn't seem to be too much moisture.
Engine starts out having about 70 lbs of pressure at just above idle and drops to 60 when warm. Get back on plane and running 3000RPM all fine, kick it down a little bit and get above 4300 and the oil pressure gauge gets erratic. Drops to 40 and will blip down to 0-10 if I stay into it, but I back off pretty quick. I have not yet hook up the low oil pressure buzzer, but would water in the oil cause the pressure to get erratic above a certain RPM (pretty consistent what RPM it happens at)? I'm running a Melling Select std/std oil pump with a bolt on 3/4 pickup. Pickup is 3/8” from the bottom of the 7qt w/filter pan. Running with no bypass into a remote oil filter (Napa Gold) through -10 Push-Lok hose then into a 2x18 oil cooler, then back into the remote adapter. Pressure sending unit in mounted above the oil filter pad and the disconnected low pressure switch is mounted in the oil filter mount. Break-in oil is Rotella T 15w40 dino.
1) I have a factory roller cam motor with the dog bone retainers. Could I loose oil pressure like this if I popped a lifter?
2) Is my sending unit goofy, this oil pressure fluctuation did not happen the day before? If there was an electrical problem, I would expect the other electric gauges to be erratic.
3) I’m planning on pulling the valve covers tomorrow to check the rocker adjustment (to check for popped lifter)
4) Does the low oil pressure buzzer come on right when the pressure drops below a certain level, or is there a time delay (what pressure)?
5) I have an oil sucker that I can stick down the dipstick tube to see if there is any water sitting on the bottom of the pan, but the oil is not milky. Will more than likely just change it.
I do not have a mechanical gauge on had at the cabin (on vacation), but I’m pretty sure the local merc dealer has the sending unit on tap. Is it just a standard chevy oil pressure sender?
Any suggestion, questions, feedback, or guidance on what I should do.
07-07-2010 | 04:10 AM
#3
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Joined: Feb 2004
Posts: 4,909
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From: Northeast,Fla
Alarm comes on at like 3-5lbs ....Change the sending unit ( it does need to match the gauge)...look for loose nut on the sending unit ....check the oil ..if its milky or high ..change it ...did it run ok after you removed the water? ......m
07-07-2010 | 09:51 AM
#5
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From: Whitefish Chain - Crosslake, MN
Oil is not high or milky.
Yes engine itself runs fine. Cruised most of the rest of the day around 3000rpm before playing around by the dock and spinning 4300+.
THe oil pump pickup is bolted on and pressed in. THe only other thing I can think of is at the higher RPM the oil pump is sucking more volume and the screen on the new pickup is somehow blocked.
Yes engine itself runs fine. Cruised most of the rest of the day around 3000rpm before playing around by the dock and spinning 4300+.
THe oil pump pickup is bolted on and pressed in. THe only other thing I can think of is at the higher RPM the oil pump is sucking more volume and the screen on the new pickup is somehow blocked.
07-08-2010 | 09:34 AM
#6
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From: Whitefish Chain - Crosslake, MN
Fixed. Flush oil with moisture out of the system and ran it. Still had erratic pressure on the elec gauge, but the mechanical gauge was spot on.
Picked up a new sending unit in case that was going to be the problem. When going down to install, I noticed the plug wires resting on the sending unit. I was running out of time for the night so I replaced the sending unit and held the wires of with a zip tie. No more erratic oil pressure. I don't know if it was the sender, but the consistency of when it would happen makes me think it was interferance from the plug wires (MSD ign).
Picked up a new sending unit in case that was going to be the problem. When going down to install, I noticed the plug wires resting on the sending unit. I was running out of time for the night so I replaced the sending unit and held the wires of with a zip tie. No more erratic oil pressure. I don't know if it was the sender, but the consistency of when it would happen makes me think it was interferance from the plug wires (MSD ign).
