low oil pressure follow-up

[jddens]

Hi Everyone,

This is a follow-up to a post last fall......low oil pressure on my starboard merc FI 350. Back ground.....after a short, fairly high speed run(32knots on the GPS) I noticed that when I went to idle on the starboard engine my oil pressure fell to about 5-10 psi. I shut it down and changed oil next day. I brought both oil filters home and cut them open....no noticeable metal particles. Next day I put in 40wt oil and new filters. when cold, oil pressure is normal, that is 45-50 psi at idle. when warm the pressure drops to about 5-10 at idle and 40+ at any rpm over 1000.

Yesterday I finally got around to checking further(afraid to confirm my suspicions...) . I removed the electronic sensor and replaced with a mechanical gauge to test.......same results. Good when cold and bad at idle when warm.......now for the confusion......after my initial test, I shut the motor down for a couple minutes and then refired and everything looked good.......25psi at idle and 40+ at anything over 1000rpm.....tested several times and everything looked good......today I will replace the electronic sensor and check again........I am assuming things will still be fine. I will follow-up this evening with today's results.

My oil level looks high when cold but ok when warm after sitting a few minutes.....could too much oil cause something like this?

I don't understand what's going on here and thought I'd seek some additional input.......any ideas????.....Thanks...........John

[Stripermann2]

It's possible that the pump pick-up's screen is clogging.

When you fire up the engine, crap is being sucked up against the pick-up screen and causing the lower pressures, due to insufficient flow, especially after running for just a bit. When you shut down the engine, the crap (debris, sludge, etc.) fall away and back down into the pan, only to continue the cycle each time you start it back up.
Have you checked this?

[jddens]

Thanks Striperman.....not sure how to check that. engines are 2000 models with less than 400 hrs.....oil looks clean......I change it with a pump down the dip stick, never had any trouble pumping it out or noticed any sludge.....confusion now is that it looks like the problem may be gone so that's what baffles me......I will know more later today..............

[Stripermann2]

Actually, you'd need to pull the oil pan and inspect...

You may want to try a good engine flush, then drain or pump out.

[jddens]

Ok, thought so......that would mean hauling the boat and pulling the engine......might end up having to do that sooner or later but it will of course be a last resort. The flush is definitely a possibility ....I have high hopes for todays test.........

[S.A.M.]

In my other boat I was reading low oil pressure on the port engine, in 2005 I put new 5.7 Crusaders in and had the same low pressure reading on the gauge. Turn out to be 18 year old wiring harness from engine to gauge.

Check that end before you do anything major.

[TADTOOMUCH]

I would check all wiring and verify good continuity from end to end on each wire and good ground on each ground wire. Then I would clean the terminals on the gauges and their connection points and tighten all connections. Then if you still have issues I would look at a new sending unit and make sure it is the proper one for those type of gauges. You can check the resistance of the the sending unit with an ohm meter at different rpms to see how it compares to the good engine.

If you put a mechanical gauge on the engine and are getting similar results though, it might be the oil pump pickup is not getting enough oil from the pan due to a plugged screen or possibly the oil cooler is not letting oil back into the pan quick enough at low rpms due to restriction in the oil cooler.

[prowlersfish]

Your boats not broke! what you have is a normal condtion some engines just carry lower oil press then others . your still with in specs . Min. oil pressuer at normal temp is 6 psi at 1000. rpm / 18 ps @ 2000 / 24psi @ 4000 rpm . I would not do a thing but run it for years to come.

as far as a pluged up screen everyone I have seen cause a loss of press. at high rpm not low.

Btw what is your idel speed ? checked with good tach (photo)

[jddens]

Thanks to all for the responses. I didn't get to check the pressure yesterday, had some difficulties getting the sensor back in and need another fitting. Probably won't get back down to the boat until Monday.

I kinda thought that since I had the same results with the mechanical gauge that I could eliminate wiring/sensor issues. My boat was completely rewired 4 years ago using anchor marine wire and connectors. Gauges and sensors were also replaced at that time. Gauges are Faria.

If I end up flushing the engine and changing the oil again, what should I use to do that?...........Thanks again...........John

[prowlersfish]

Unless you have gotten water in your oil I would strongly recc you do not flush your engine. I have seen engines damaged by doing so. If you had the screen being pluged up you would be lossing oil pressuer at higher rpm . Unless you have had a bad over heating issue or have been real bad about oil changes I do not think you have a blockage .I still wonder if you really have a proplem as you pressuer is in spec . do you have any abnormal engine noises ? .

I Have GM tech for 30 years and nothing you have said makes me think you have anything to worry about . Maybe I am missing something ?

is idel droping lower then it was ? comeing off a high speed run your oil will be hot and thin . after you idel a while is the pressuer higher ?
are you running 40w or 10w40 ?

[gjrylands]

I agree with Paul. Flushing with anything but oil will only damage the engine. Anything you use to flush the engine will break down the oil. Running the engine that way can cause bearing damage.

Even if the engine has water in it I wouldn't flush it with anything but oil. Change the oil and filter. Run it a few minutes at idle and check the oil. If there are any signs of water, change it again. (It will look like a chocolate shake.) Repeat until the oil is free of water. You may have to change it a few times, but oil is a lot cheaper then an engine.

[jddens]

No water in the oil....something has changed........pressure at idle used to be 25. Then after a high speed run it dropped to 5-10. Currently running 40wt. normally run 10-40. Oil gets changed annually and that's only 20-30hrs. I won't flush it........Monday I will put sending unit back in and test........idles at 700-750rpm.

[alexander38]

just a thought does your oil filter system have a automatic bypass system in it. mind has them it's a ball and spring valve that could be getting stuck at low rpm after running at high rpm.

[prowlersfish]

After you come off a high speed run and the press. drops will it come back up after you idle a few minites ? Did this happen after changing brand/type of oil ? make sure the leavel is correct ( better slightly low then over full due to foaming isses)

[jddens]

Oil pressure does not back to normal after idling for awhile.......as mentioned awhile back, after testing with a mechanical gauge (with same results as the Faria elec gauge) I shut down and restarted after about one minute and everyhting appeared normal. That is 25 at idle and 40+ at any RPM over 1000......this was the first time oil had been normal since problem developed.....I did that several times and it stayed normal. .maybe had some gunk in the sending unit????...I'm hoping to get the sending unit reinstalled tomorrow and am hoping the problem will still be gone.............

I'm not sure about a bypass valve??? My motor has 2 oil filters mounted on a bracket behind the distributor, would the valve be in that assembly?

Also, oil level appears to be high when dead cold and good when warm after sitting a few minutes. It is possible that it is too full. If problem continues after sensor is installed I'll pump some oil out and test again. Capacity with the double filter system is about 7 quarts.......

Thanks again for all the good suggestions............John