dropped oil pressure!!!!!!

[alilley]

ok motor was freshly rebuilt (for detail please see one of my other threads) and finally for it wet. So we idled out of the marina to get pas the no wake marker. and rolled into the throttle to about 1/2 throttle ran there for for about 5 min and all was good. Temp holding at 150/160 mark oil pressure holding a solid 45 . So i figured go wot (topped out at 4100 rpm) and we did ran strong for about 5 min then since we was going to dock at the house to make dinner, (and go back after) rolled back out of the throttle to idle, and docked it at the hous.......dad stopped by for dinner and i had left something in the tow vehical. since dad helped rebuild motor i figured take boat over so dad can hear and listen to motor under normal situtations. It did take a but longer then normal to start. So we idled out of the cove and and once we got to the main body went to wot. There was me (about 280) dad (about 160) 16 year old son (maybe 150 if he is lucky) his lady friend (about 100) ad my 4 year old (about 45) and we was all sitting in the rear half of the boat. I noticed that it took a little longer then i had figured that it should to plane out. after it did hit the same rpm as before then i noticed that it was slowly backing the down and i looked down and oil pressure was down a little and i backed out of the throttle to about half and when i did oil pressure dropped to about or less then 10 psi granked on it a time or 2 and oil pressure guage only jumped and went back down. first thing that was checked was the oil its self and yes it was dead on where it was when we pulled out and still had the nice carmel coloring to it.

- what would cause a motor to drop oil pressure liike that after havein about 1.5 hours of run time on it?

 

[StevNimrod]

Re: dropped oil pressure!!!!!!

First things first: if your current gauge is electric, hook up a mechanical pressure gauge to verify that what it's telling you is what is actually going on.

 

[paultjohnson]

Re: dropped oil pressure!!!!!!

I think you went to WOT way to soon on a fresh rebuild, You need to give it some break in time to give the rings time to seat etc.

 

[mkast]

Re: dropped oil pressure!!!!!!

You need to give it some break in time to give the rings time to seat etc.

What do piston rings have to do with oil pressure?
Normally, bearing clearance/condition will be indicative of oil pressure.
Was a new oil pump installed during the rebuild?
As mentioned, a mechanical gauge will verify oil pressure readings.
Mercruiser states a minimum of 4 psi at normal operating temperature at idle and the rule of thumb is 10 psi per thousand engine RPM.

 

[alilley]

Re: dropped oil pressure!!!!!!

new oil oump, and all bearings except cam bearings (they were still in really good shape) were installed. Everything was within in clearance. and going to wot right out of the hold like (i think) should not have been an issue since they do dyno pulls after breaking in cam shafts all the time

 

[mkast]

Re: dropped oil pressure!!!!!!

should not have been an issue since they do dyno pulls after breaking in cam shafts all the time

What THEY say, what THEY do and reality, rarely coincide.

 

[paultjohnson]

Re: dropped oil pressure!!!!!!

What do piston rings have to do with oil pressure?
Normally, bearing clearance/condition will be indicative of oil pressure.
Was a new oil pump installed during the rebuild?
As mentioned, a mechanical gauge will verify oil pressure readings.
Mercruiser states a minimum of 4 psi at normal operating temperature at idle and the rule of thumb is 10 psi per thousand engine RPM.

I agree with your statements, however, I was making more of a general statement that going to WOT on an engine that's only been run maybe 10 min on a fresh rebuild, then leaving it at WOT for an extended period of time is pushing it. It doesn't give the bearings time to , whats the word... polish ... themselves. To get used to working with each other [crank and bearings] putting a big load on the new piston rings before they seat them selves can force combustion gases past them, and you may never get 'em to seat properly. You can end up with an oil burner..compression issues. Admittedly I am more old school, but I don't recall any engine manufacturer or re builder recommending to take a new or rebuilt engine, and running the dog snot out of it right out of the gate...Maybe after 2 - 5 hrs of running, BRIEF periods of WOT contribute to a good break in. But NEVER sustained hi speeds. Speeds need to be varied, engine allowed to cool down alot But like I said, I am Ol' school.........

 

[alilley]

Re: dropped oil pressure!!!!!!

ok this will clear a few thing up before this gets into a real confusing mess.....

http://forums.iboats.com/showthread.php?t=483350

that is the thread that i started the end of last week that wanting to know what to look for when i put it on the water.

the motor had about a hour and a half (at least) run time on the muffs in the drive.

my next question is

- does the 3.0/181 have a history of starving for oil if it is sating a littler longer then it should to plain out? when i went tho throttle it up to get it up to speed it stood the bow up for prob 4-5 sec at about 2500 rpm plus. my thinking here is....since the sump for the oil pump for this motor is in the front, when the bow stood up all the oil went to the back and sucked air and in turn took out the bearings....can someone please give me a few thought on the theory and thanks

 

[StevNimrod]

Re: dropped oil pressure!!!!!!

The theory can be right all day long, but if inaccurate data is used to form your theory then it is meaningless in practice.

In theory, if there is no oil at the pump, there should be no oil pressure, and your bearings should be toast. That should be pretty easy to spot pulling the oil and filter or you can tear into the engine again.

Also in theory, if your oil pressure gauge is lying to you, then you don't have a mechanical problem to begin with and you can focus on solving the actual problem.

We can keep guessing at what it might be, or start finding out what it is.

Either way, there has to be some sort of method you use to your troubleshooting or you risk spending a lot of times chasing the wrong problem (or one that doesn't exist).

The attached is the oil pressure troubleshooting page from the FSM for a 4.3 engine. The jist of the page should be the same for your engine. Particularly the first line.

View attachment oil pressure.pdf

 

[alilley]

Re: dropped oil pressure!!!!!!

i should have added this to my previous posting.......my bad.....but in my defence it had been a long day and i was tired as i had been running around town.....who ever said that vacation was fun

so it sounds like i just need to get my butt into auto zone or some place like that and pick up a mechanical oil pressure guage get it hooked up and try it again.

should i unhook the coil wire so it dont fire up? this is just to prevent any further damage and i recall before i let it fire the first time i did the same thing to "prime the oil system" and it it in the 40 lbs mark just off the starter. or shuold i get an old distribuator (i do have one from old motor i tore appart) stick itin the hole hook drill to te other end and spin it to see what it shows? which way will be better?

 

[StevNimrod]

Re: dropped oil pressure!!!!!!

Here's what I do (others may do it differently or point out something I left out):

1. Remove the oil sending unit (for the dash gauge) and install a brass tee fitting in it's place.

2. Install the oil sending unit in one port of the tee, and hook your mechanical gauge hose to the other port of the tee.

3. Start the engine and note the readings from both gauges. Also try to repeat what you were doing when you noticed the pressure issue on the dash gage.

4. Note any difference between what your dash gauge is reading and what your mechanical gauge is reading.

It will be clear once you get the mechanical gauge how it should all go together. If not, I can probably post a pic later.

 

[alilley]

Re: dropped oil pressure!!!!!!

ok....so i got a mechanical oil pressure guage hooked up, totally unhooked the electric one. I also put a new battery in it (the old one would not hold a charge) reached over hit the key, guage did not move. friend of mine thought it was due to the air in the line so he unhooked the line from the back of the guage (with motor runing) and i only filled the line about 1/3 of the way. We reached over and hit the key to kill it. When we started the oil still looked faily new, after it was all dark and metallic looking. Now with my auto experances i am assuming that the metalic looking stuff is bearing meteral? and it sound like to me it is time to pull the motor and stick another set of bearings in it but now for m y new questions

- y would a new oil pump stop working?
- other then bearing and figuring out y the pump stopped what else should i lookin into replacing?

 

[alilley]

Re: dropped oil pressure!!!!!!

update.....i just pulled the distrubator out to see if maybe the piece that drives the oil pump broke off........well it is still intack.

other then a falty oil pump (this is a new melling oil pump) what else could it be?

 

[alilley]

Re: dropped oil pressure!!!!!!

ok so dad had one of the tools to spin the oil pump with out starting th motor. I stuck that in with a drill hooked up to it and spun it both ways. . . . . . nothing on a mechanical guage . . . . . .so i then though maybe (just maybe) a plugged oil filter i took it off (runnig the risk of a huge oil mess in the bilger) and tried it again. . . . . . . .still nothing on a mechanical guage the drill didnt hardly pull down with either test. . . .i thought from my previous auto builds that it should really pull the drill down


does any one have any thought what could have caused this other then a bad oil pump?

 

[alilley]

Re: dropped oil pressure!!!!!!

any idea what could have caused a new pump to stop pumping?
what else could it have been?
with this being a new marine oil pump that was purchased with warranty, any idea or suggestions what i should do about getting it fixed?

 

[wca_tim]

Re: dropped oil pressure!!!!!!

Did you drop the oil pan? maybe the pick-up fell off? Just a thought...

 

[alilley]

Re: dropped oil pressure!!!!!!

i have not pulled the motor........yet i figured that would prob be my next step. i thought the pick might have came off. dad was the one that put that on there (i was at work on the road) he said that it was good and tight and was bolted in place not like some he has done in the past where they just stick in the pump.

when i pull the motor should i just put a new set of bearings (both rod and mains), new rear main seal, oil pan gasket, fresh oil and filter, and another new pump? now i am not for sure if a rod is "knocking" or not but, if there is one loose when i tear it appart do i still just replace the bearing or do i need to replace the crank and that rod as well?

 

[wca_tim]

Re: dropped oil pressure!!!!!!

will have to see what it looks like.,..

 

[backyard mechanic]

Re: dropped oil pressure!!!!!!

If there is metal in the oil you have an issue with bearings. If you had no oil pressure when you ran the boat at WOT you lost your bearings then. Could reason that a 5-20 multi grade oil got warm and thinned out thus loosing oil pressure but NO oil pressure is a definite problem. Could be; Oil pickup dropped off, baffle plate is blocking the oil pickup, or excessive clearance in the bearing lands or cam bearings. I suppose the rod bearings could have rotated around or were not installed correctly. Perhaps oiling holes were not lined up on install? Sounds like you are in for a engine removal for sure.... Sorry man. That sux!

 

[picklenjim]

Re: dropped oil pressure!!!!!!

Bottom line is at this point the engine needs to come back out. Without removing everything turn it upside down and remove the pan. Initially I would have thought it to be a spun bearing. I remember your original thread when you were doing the rebuild and I mentioned the unusual wear on the bearings and recommended the crank at least be polished.
Now though you said you took the oil filter off and spun the pump and still got nothing. Oil should have been pouring out where the filter mounts reguardless of the condition of the bearings. Also the drill not having any resistance makes it seem as something broke with the pump. I burned a 1/2" drill up one time spinning a high volume pump in a big block. If something with the pump did go wrong it most likely took out the bearings. If so it probably also scored the crank. May have to have the crank reground and use the correct bearings for the regrind. You can also have your rods resized if needed. With the pan off you can pull the main and rod caps and inspect. Then you can determine If you need to disassemble the entire engine. Usually it's a good idea to tack weld the pick up to the pump even if it does bolt on. The thin metal pick up bracket can crack.