Trojan Boat Forum

Bad news....looks like I may have hurt the starboard motor in my F30. I was making rare, short, WOT run at 30 knots GSP and 5000 RPM both port and starboard for about 2 minutes..... Everything was fine until I throttled back, then the starboard motor's oil pressure went south. Ok above 1000-1200 rpm almost nothing at 600-700 rpm idle. Temps were fine the entire time. I have to go through a no wake zone so I shut down the starboard motor and went in on one. Fired it up for a couple minutes to get into my slip. After the motor sat for an hour I started it and the pressure was better but still not right. Next day I changed the oil and filters and replace the 10-40 with 20-50. Took a test run yesterday, the new oil helped but still very low under 1000 rpms..........I cut open the used oil filters and didn't see any metal. The gauge is working properly.......I think this motor will need to come out for a rebuilt ....but thought I see if anybody has any ideas on how I might be able to nurse it along for awhile.......pressure is ok above 1000-1200 rpm not as good as it was but ok.....motors are throttlebody injected merc 350's, 330 HP each.........maybe 40wt and slick 50???.........Thanks.............JD

Have your tried checking the oil pressure with a different gauge? Also your might check the oil pump and pickup tube, you may have a clogged pickup tube

Thanks Willie......haven't tried a diff gauge yet only because it acts normal, good pressure when cold then falling off as it warms up......to check the pump and pickup tube I have to drop the oil pan right?.....no way to do that with the motor in the boat.......

Hmmm.. seems to me the only thing that is wrong here is the gauge reading at low revs. All your other checks have not shown any problem.
If the engine sounds fine and accelerates fine (no odd sounds) then you may have a problem with the oil sensor/sender.

I have the opposite problem sometimes it stays up on one engine when I throttle back. Which means were I to loose pressure I could be oblivious to it. Cause is a sticky piston in the oil sensor switch. As it's an on again off again problem I don't worry too much.

As long as it goes up as you increase revs I would not worry. I suggest you should change the oil sender before going as far as pulling the engine.

I agree with ready123. I have had engines idle with accetable oil pressure but drop when rpms go up. This is bad-ness, broken-ness, kaput-ness.

Along with this scenario came a bronze glaze to top old oil when I changed it, and you all guessed it.........wore out bearings......The oil seems to tell the rest of the story.

Also for the record my oil psi senders have a tendancy to stick and jump. I proved this by hooking up a temporary mechanical auto zone gage to compare.

I think you hurt the engine. You can try to switching the oil preasure sending units of one engine to the other. If the oil preasure problem switches to the other engine, the sending unit is bad, but don't count on it. You could try the 40 weight oil and additive, but it's a bandade. You don't want the engine to seize up. you'd be looking at an engine replacement rather then an engine rebuild.

Oil preasure drops when you get wear on the bearings. A looser fit means that oil can squize out between the bearing surface and the journal This causes the preasure to drop. When the preasure drops the lubercation falls. That causes heat. This is not the engine temperture that you read on the gauge, but internal engine tempertures. When the tempertures get high enough the bearing welds to the journal. Then it's too late.

Thanks everyone for the input.....I have a mechanical gauge I used to use when building engines.......I will try the mechanical gauge first....if it reads like the current gauge then I will assume the engine is damaged. I will still try the 40wt and slick 50 as a band-aid and cruise at hull speed, nothing over 2000rpms..... I just hauled the boat for bottom paint and zincs 3 weeks ago. What with the holidays and being layed off/retired I don't have the bucks for a rebuilt right now.....maybe I can limp for awhile. This is a big disappointment, the engines only have about 350 hrs......guess I learned my lesson about WOT....Thanks again and I wish you all a great Thanksgiving............John

John ... good luck with your findings. Happy Thanksgiving to you and yours.

you were running that engine at a very high rpm,,,,, anything is possible,
check pressure with a diferent gauge and have a technician look at it

Isn't there a oil pump? Could it have gone bad? I do a lot of troubleshooting and I am not a parts changer. I would like to know what caused the problem and what really is broken. Engine or oil pump.

oil pump failure is not likely as there are very few moving parts in the pump, only two gears which are driven buy a shaft, if the shaft would have broken you would have no pressure at all, and this is not your case,and it is not likely that the gears are broken,
another posiblility may be the screen pick up on the oil pump is dirty, but again, unlikely,
what makes an engine loose pressure is typically worn main bearings
on the crankshaft

Well that sorta elimates the oil pump. Still I am just wondering. I agree it probably is the engine but just trying to eliminate everything else.

I got this info from the following site:
http://www.aa1car.com/library/2005/us020516.htm

Possible causes of low oil pressure include:

Excessive main and rod bearing clearances (someone may have installed the wrong-sized bearings or standard-sized bearings on a reground crankshaft). Only 0.001" of extra clearance in the main bearings can reduce oil pressure by up to 20%!

Excessive camshaft bearing clearances (a bearing may have slipped out of place when the cam was installed).

Excessive clearances inside the oil pump.

Leaks between the oil pump and engine.

Oil pump relief valve stuck open or installed backward.

A loose or mispositioned oil pickup tube (too high in the oil pan).

A defective oil pressure sending unit or oil pressure gauge.

Low oil level in the oil pan.

Cracks or leaks in the oil galleries or gallery plugs.

Cracked oil pump housing (improper installation).

Oil viscosity too thin for hot weather.

Oil viscosity too thick for cold weather.

Hope it helps,
Matt

Thanks everyone for the input.....as it stands right now I am assuming I have bearing issues. Oil pressure it good at start up when cold. As the engine warms pressure begins to drop......at all times pressure is ok at any RPM over 1000. The problem is when warm at idle, then it almost drops to nothing. I haven't had the chance to check further but my next step will be to try a mechanical gauge.....if still bad I'm considering heavier oil and a couple cans of slick 50 and keeping under 2000 RPM and watching the gauge like a hawk.......I don't want to ruin the engine but I also don't want to spend the thousands of $$$ right now to pull and fix it...........Thanks again.....John

Well it sounds like there is a lot of information on this subject. Anyway I am sure it will eventually be solved.