No oil pressure. 2008 Mercury proxs 250

[denny7250]

Alright Im having problems with low oil presure. I am not getting any oil back to the return tank on the motor. When i checked the pressure hose to the main tank I was not getting pressure. I replaced the check valve on the block and started recieving pressure back to the main tank. This however still would not push oil back to the tank on the motor. The main tank and all lines where thoroughly checked for air leaks. No leaks where found. Now the weird part. After running the boat for about 15 mins the check valve stopped working again. So I took the boat to my local mercury dealer. They have worked on the boat for the last two days with no results. They changed the check valve and it started working again, but its still not pushing oil back to the engine. They have aslo checked for air leaks in the tank and checked engine compression. Everything was fine. Any ideas on what else we may need to check would be appreciated

[Savage]

Did you replace the DIRECTIONAL oil filter, that is in the BLUE striped oil delivery line, feeding the motors oil reservoir?

[denny7250]

No but i checked it and its working

[OldTimer57]

This can't be that hard to find. Take the lower unit seal pressure tester and hook to the hose coming from the engine. Take the hose going to the engine tank loose. Pump the pressure tester. If no oil comes out, that has to be easy to find. Either the pressure is not getting to the tank because something between the engine hose and the tank is clogged, or if pressure does get to the tank, but no oil back to the motor, that is stopped up. No reason they should be spending 2 days on this nonsense.

[denny7250]

Trust me I know. I dont have alot of confidence in my local dealer. The motor did seem to run a little rough at idle. I wonder if it could be a broken reed.

[Savage]

No but i checked it and its working

How did you check the oil filter to know it's working ?
Check the pickup tube/strainer inside the boats remote oil tank for cracks, or blockage.

Oil will not flow from the Remote oil tank to the motors oil reservoir unless the air is bleed from the motors oil reservoir.

Click on this >>>> How to BLEED the ENGINE MOUNTED OIL TANK when AIR IS PRESENT

[denny7250]

Yes the cap was loose. I applied a little pressure (6-10 psi) with a hand pump on the supply side and it pushed oil back to the engine tank. The pick up screen is also clean.

[Savage]

Did you try disconnecting the SOLID BLACK hose, where it connects to the block mounted check valve, and apply pressure to the hose at that connection point? This would simulate pressure coming from block mounted the check valve.

[denny7250]

Yes thats where i applyed pressure. It seams like it may not have enough crankcase pressure. I dont have anyway to check the crankcase pressure. Im hoping the shop will check it. Thanks

[vicsservice]

Hmm it does sound like low crankcase pressure,, check out that fuel pump diaphragm could be ripped
bleeding crankcase pressure off?

[OldTimer57]

A simple pressure gauge hooked to the OUTPUT from the engine block will pin the tail on that donkey. I have a gauge I've used for that that goes to maybe 10psi max so it can measure those sorts of fairly low pressure. There's certainly a spec for what this ought to be. If the pressure coming out of the block is bad, then the possibilities shrink. Certainly a split diaphragm could do it (as above). Or a split reed which allows back flow and reduced pressure come to mind. And if you have been inside the engine, perhaps a gasket is compromised (i.e. reed blocks, intake, etc... Not sure how the 3.0's route those little bleed hoses, but they can bleed pressure if they pop off.

[EuropeanAM]

Please see the Forum Announcements, and be sure to provide the REQUIRED info when posting. Thanks!

Install the gearcase pressure tester on the pressure line (the one that connects to the check valve in the crankcase).

Pressurize to 6 psi WITH CAPS CLOSED. Check for pressure leakdown (if leakdown occurs in a couple minutes, LOCATE THE LEAK).

Since you're failing multiple check valves, it's very likely you have one of the following:

-Breach in one of the fuel pump diaphrams

-Broken or damaged reed on #6.