Low Oil Pressure on Throttle Cut Back

[Tman]

While cruising the lower Hudson today at 2560 RPM (80% load) both engines(synchronizer on), I had to quickly pull back on the throttle to avoid a log strike. When idle speed was reached, a low oil pressure alarm sounded and registered for both engines on the Smart Craft. The oil pressures registered roughly 12psi in both....they eventually crept back up to 20-ish. The audible alarm ceased and all was normal again. At cruise, the oil pressures are typically 40-42 psi..which is normal.

This is the second time such an event occurred. The first time (300 hrs ago) was on its sea trial and followed a very similar deceleration.

Oil and other regular seasonal maintenance performed religiously. Engines run very well and producing essential spec performance with the exception of this low oil pressure alarm following an aggressive deceleration.

Any thoughts on the problem? I'm thinking something in the computer sending a feed forward signal to the oil pumps to cut back....only they cut back too quickly or much resulting in the low pressure alarm. Is this a calibration issue?

Tom

 

[capecodcruiser]

I have had same problem/conditions on my 2001 310 with 350 mags. Only one engine does it. I have searched high and low for the problem. Very strange. Hope we get some theories on this.

 

[390x]

I would suspect a possible blockage in the oil cooler. Have you shelled any impellers lately? If so, did you recover all the missing blades if there were any? The oil pressure could lower when the oil is really hot, and then as it cools, the pressure eventually comes back up.


Or you could just start running 60 weight oil and it won't drop. :grin:

 

[ZZ13]

I have been told by many mechanics, both automotive and marine, that this is normal and not to be concerned about it. Explanation given was that oil pressure is a function of rpms and temperature. At startup, oil is cold so higher pressure exists even at idle. When warm/hot then I was told to expect about 10psi per 1000rpm as a rough rule.

 

[kevin27]

This sometimes happens to me after cruise throttle cutback. The oil pressure drops to 15-18psi and the light comes on. If I bump up the rpm slightly the pressure returns to 20 psi and light goes out. As soon as oil temp comes down I will stay above 20 psi at low idle(600 rpm). Less than 60 sec for this to happen.

 

[Tman]

Good feedback. Although it only happened twice, it's one of those quirky events that can be irritating....not to mention the alarm audible which makes one jump when it sounds considering the focus is on not running over a deadhead in the way...last thing you need is an engine alarm.

The unique(somewhat reassuring in an odd sort of way) circumstance of this event is that it occurs in both engines, not just one. So either (1) it's normal, (2) some feedback signal sent to both engines is off calibration, or (3) some wild coincidence that both engines(oil pumps) have a problem.

Tom


Sent from my iPad using Tapatalk HD

 

[kevin27]

It has more to do with oil temp.

 

[src]

As the oil heats up, it becomes less viscous, especially "straight grade" oil. Lower viscosity = lower pressure in the system (compared to higher viscosity oil or colder oil). That's one of the reasons cars use multi-grade (10W40, instead of straight 40 weight). It's possible that you might be running the wrong weight of oil based based on your environmental and running temperatures. Another possibility is that you are running the right weight but the lower viscosity of hot oil, combined with a weak oil pump, could cause pressure drops during off-throttle situations.

 

[kevin27]

This only happens at low rpm only. I have the low idle set as low as possible so my trolling speeds are better for some fishing situations. When at operating temp I am usually at 600 rpm low idle. So with hot oil from cruising long periods pulling back to 600 rpm sometimes it drops below 20 psi for a very short time. Not a big deal. I still have positive pressure. Trust me it' s not hurting it. I have lots of experience with complex equipment and understand engines and systems very well. If something was wrong I would fix it right away.