Oil pressure dropping off while under way

[viper1216]

Hey guys,

Quick question....took my boat out today into the bay. Boat was running great for about 2 hours or so. On the return trip I noticed that the oil pressure was dropping down to between 0-20 (first hash mark). Was running at about 3k RPM. If I let off on the throttle, it would go back to 40. But if I increased the throttle it would drop back down again. I didn't hear any knocking and she was running great. It was really choppy in the water so we were bouncing around quite a bit. Oil level is right up where it needs to be and was changed in March. Oil has about 10-15 hours on it. Not sure if it was just the boat sloshing around causing the oil to move around in the pan, but just want to make sure. Engine is a 2010 3.0 with around 65 hours on it.

Thanks for any advise!
Dave

 

[spoilsofwar]

My first suspect would be the oil pressure sender. Second would be the gauge itself.

The oil in the pan moving really has no effect on pressure unless the level is so critically low that the oil pump pickup is occasionally exposed to air as the oil sloshes around. Since the pickup is located deep in the pan, you would have to be very, very low on oil for this to happen.

 

[viper1216]

I was thinking the same on the oil slosh. I originally thought it was low on oil, but checked when I got home and it was right at the top of the hash marks. Gauge is new....just put in a few months ago. For the sender, any idea why it would only do it under acceleration and then fine when I get off the throttle?

 

[spoilsofwar]

For the sender, any idea why it would only do it under acceleration and then fine when I get off the throttle?

Assuming it's an electrical and not a mechanical gauge, it could be a poor connection or wire moving around as the boat gets up on plane or drops off.

 

[viper1216]

Hmmm, makes sense. It is electrical. I was just checking it out. It appears the sender is on a T setup...I'm guessing one is the sender the other an alarm or something. I was able to move the T around where it connects to the block...so it's loose. I'm wondering if that may be the issue...Going to take it all apart, and as long as it's not an arm and a leg, I will just replace the sender in the process.

 

[gm280]

Sounds like the "T" setup does need some attention. Is there any possible way your oil is thinning out when warm? How hot is the oil getting? That would cause those issues. :noidea:

 

[Bondo]

I was able to move the T around where it connects to the block...so it's loose. I'm wondering if that may be the issue...Going to take it all apart,

Ayuh,.... The sender, 'n switch needs a good solid Ground to work,....

With a loose fittin', How good do ya think the ground path is,..??

Take it apart, 'n reassemble with thread paste, Not tape,....
Bet it'll work alot better then,.....

 

[bruceb58]

What viscosity oil are you using? Synthetic or Dino?

 

[viper1216]

I was wondering about the viscosity. I'm using the same oil that the previous owner was using....QuickSilver Synthetic 25w40 (will need to confirm the weight when I can look at the bottle, but pretty sure that is it). He only used the boat in the pond though, and I'm assuming probably a lot shorter time intervals with it running, than me in the bay. Maybe I should change it, or add something to it. I thought I read not to use synthetic...but can't remember if its a quality thing or just not worth the money thing.

 

[Silvertip]

A weak oil pump pressure relief valve spring might cause this. As long as the engine is at low rpm the spring holds normal pressure. As the engine rpm increases, so does pressure until the spring prematurely releases pressure. You need to verify pressure with a mechanical gauge.

 

[viper1216]

Ok, came home and double checked the oil type. It is Mercury Synthetic Blend 4 Stroke Outboard Oil 25w-40. I also picked up some thread paste to redo that T setup. Where would I find the Oil pump pressure release valve? Is it part of the pump itself, or something I can check or replace seperately?

 

[viper1216]

Also, is that oil sufficient? The guy I got the boat from gave it to me to change the oil. Looks clean as a whistle.

 

[spoilsofwar]

Anything regarding the oil pump, pressure relief valve (which is internal and would require engine being pulled to examine) included is absolute last thing to suspect on a 65 hour engine. Basically ignorable until everything else has been ruled out.

However, verifiying pressure with a mechanical gauge is always a good idea.

 

[viper1216]

Anything regarding the oil pump, pressure relief valve (which is internal and would require engine being pulled to examine) included is absolute last thing to suspect on a 65 hour engine. Basically ignorable until everything else has been ruled out.

However, verifiying pressure with a mechanical gauge is always a good idea.

Roger that. Can I add another T to the existing T to add the manual gauge? I'm out of spots to put it on.

 

[spoilsofwar]

Roger that. Can I add another T to the existing T to add the manual gauge? I'm out of spots to put it on.

Personally, to avoid any more plumbing then necessary, I would just temporarily plumb in a mechanical pressure gauge in place of the current electric oil pressure gauge sender.

 

[viper1216]

Hmmm, good point. There are 2 things on the T...the sender and another component that has a spade connection type wire....is that an alarm or something? I would prefer to leave the sender in place so I can compare with the mechanical so maybe I can take that off and put the gauge in it's place

 

[spoilsofwar]

It is likely the alarm, yes. sounds just like the sensor on my motor, with the spade connector on it. If you pull that off while the motor is running it will sound the alarm. It won't effect anything else, but man are they loud... Don't think I'd want to be troubleshooting with that thing sounding off sustained. But maybe you've got a good set of earplugs

 

[Bondo]

If you pull that off while the motor is running it will sound the alarm.

Ayuh,.... Ya got that backwards,..... Pull the wire it can't sound,.....

The switch goes to ground to sound the alarm,.....

Just as the sender, they need a solid ground to work,....

 

[spoilsofwar]

Ayuh,.... Ya got that backwards,..... Pull the wire it can't sound,.....

The switch goes to ground to sound the alarm,.....

Just as the sender, they need a solid ground to work,....

Thanks Bondo. Makes sense. And, even better for the OP then.

 

[viper1216]

Took everything apart today. The T adapter that connects to the engine was extremely loose. I took it off by hand. Cleaned everything up and used thread paste on all the connections and put it all back together. Replaced the oil sender since I had it all apart anyway. We shall see on the next run if all is well.