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5.7L MPI Oil Pressure Drops

TS2900

New member
I am chasing an oil pressure problem. I have connected a separate oil pressure gauge to eliminate any pressure gauge issues. The oil pressure issue does not show up unless the engine is run for about an hour under a load. The oil pressure starts fluctuating and eventually falls to zero. The engine temp does not overheat or really change at any point once the engine is warmed up. I have changed oil viscosity, oil filter, oil sludge remover and nothing seems to effect it. Once the pressure drops to zero there is no valve chatter suggesting a loss internally of oil pressure. If I pull the throttle back to idle the oil pressure returns to normal. The engine can run all day below 3000 rpm and will not drop. The drop occurs only above 3000 rpm. Some have suggested oil pump or pick up tube problem.... the problem is, to check those items off the engine would have to be removed from the boat. Not enough room to lift and pull the pan and the engine compartment deck also has to be removed. The boat is a 2001 Tiara 2900 open. Any suggestions would be appreciated.

Oil Pressure Drop Video

Oil Pressure Gauge is the Top Left Gauge. Oil Temp is the Top Second From Right Gauge


Thanks,

Tony
 
link to video didn't work....for me anyhow.

was the second gauge showing the same drop as the original? what kind of a gauge is it?

Where (which port) did you hook the second gauge to?

based on the little bit of info in your post, I'd be inclined to think your oil pressure is ok.....lack of oil pressure usually triggers valve chatter in short order...
 
link to video didn't work....for me anyhow.

was the second gauge showing the same drop as the original? what kind of a gauge is it?

Where (which port) did you hook the second gauge to?

based on the little bit of info in your post, I'd be inclined to think your oil pressure is ok.....lack of oil pressure usually triggers valve chatter in short order...

Sorry, the video was set to private. You should be able to view it now. If not, let me know. Both gauges showed the same drop and pressures. It is a mechanical gauge connected directly to the T-fitting on the block.
 
Same reading on both gauges suggests the drop may be real. Sounds like it could be low oil level (at high rpms the oil does not drain down fast enough to keep the sump level above the pickup), Is your 5.7 the flavor that has two dip stick tubes (one on either side). If so, these lead to a "t" and can get cockeyed and you can register a 2 quart difference between them. You might try thowing another quart in to see if the readings change. (This is probably not it, but it is a cheap test)
 
It does have two dipsticks. I will add another quart and give it a try. I think I did this in the beginning and it did not make a difference. Are you able to use either tube? If so, can't I just check the level between the two tubes and see if there is an oil level differential? Is it possible that it is overfilled and the oil is making contact with the crankshaft and causing the issue?
 
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Sure you can use both dipsticks. I just average mine. As for too much oil....you are beyond my experience. Others may chime in with some observations. Logic would suggest you could get some foaming and perhaps some erratic readings, but I don't really know.
 
if there's too much oil in the pan, yes, it can get aerated and that will cause a pressure drop. the windage tray is standard equipment but can only handle a 'little excess'.....

I'd be inclined to move the mechanical gauge to a different port (there used to be one on top the block, back by the distributor, where the rear of the intake is)... and see if they still track.

The aeration is a definite possibility, given as the pressure comes back up after the rpm goes down AND it happens while under load, up on plane.

how much oil do you normally put in when you change the oil? How much normally comes out?
 
It takes 6-7 quarts if I change the filter to get it to the midway mark on the dipstick. Is there a way to tell if it is aerated (bubbles, etc.)?
 
I would think you would be able to see the foaming to some extent.....honestly, its been a couple decades since I saw aeration firsthand....

Some of the newer oils have better anti-foaming agents than others so the'bubbles' may not last long at all.

The last owner's manual I have in that timeframe is 2003 - it shows two different oil capacities depending upon your oil pan - steel or aluminum - any idea which one you have?
 
Checked the oil level from the second dipstick location and the level is about an inch past the full mark and the other location is at the full mark. Going to pump out some oil and get it at the mid mark on the second location and test it. That will put it below the add mark on the other location. The book calls for 4 quarts and then add as needed to get to the full mark. It took about 7 quarts to get it to the full mark before on the dipstick location I was using so I assume it is just over filled. I have the steel oil pan.
 
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Agreed - steel pan needs 4 qts....with the filter....I can't believe it needs three more quarts to get to full
 
Well.... Both engines have the dual dipstick setup. Both engines have the same oil level issue. When checked, they both showed overfilled by about an inch on the left side and mid level to full on the right. I drained the oil on both engines so that the dipstick on the left is mid level. The right dipstick on both sides is at or below the add level. I took it for a run for over an hour under a load and the oil pressure did not fluctuate or drop to zero like before. Hopefully this solved the issue. I will know more when I head offshore again and the engines run under sea conditions all day. I did notice that the oil pressure on both engines falls off to 20 psi when I pull the engines back to idle. Before the oil pressure on both engines would stay at 40 psi when pulled back. So there is a difference in how the oil pressure responds when reducing speed. All within specifications throughout the range. Just different.
 
Its not unusual for the oil pressure to drop some, with reduced RPM, once the oil is hot....when it gets hot, the viscosity lowers and your gauge shows the results....
 
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