0 oil pressure any ideas

[Sunset Bob]

I have a 1997 Larson that on a cold start has good oil pressure but after about 15 minutes of running at about 3000 rpm oil pressure starts to drop(about 20 PSI at 3000 rpm not good need 10 PSI for each 1000 rpm) Pull throttle back to idle and 0 oil pressure.
Engine burns no oil
Engine has plenty of fresh oil
Engine has no bearing noise
Engine does have some lifter noise at 0 oil pressure
WHAT NEXT

[NightWing]

After the pressure drops to zero, shut it down and immediately check the oil. I would bet it won't even show on the stick.

Your symptoms describe an engine that is sludged up on the top end and the oil is not draining back quickly enough. Pull a valve cover to confirm this. If the engine is sludged, the top of the head will be covered in sludge and the drain holes will be partially blocked.

[Resident 2B]

Originally Posted by NightWing

After the pressure drops to zero, shut it down and immediately check the oil. I would bet it won't even show on the stick.

Your symptoms describe an engine that is sludged up on the top end and the oil is not draining back quickly enough. Pull a valve cover to confirm this. If the engine is sludged, the top of the head will be covered in sludge and the drain holes will be partially blocked.

NightWing,

This is exactly what I think is happening. All the oil is stuck up top and cannot get back to the sump pump.

R2B

[Sunset Bob]

I thought this also but then it happens the valve covers are not flooded.
I haven't pulled a valve cover but looking in through oil fill it looks clean.

[Blue Thunder]

Originally Posted by Sunset Bob

I have a 1997 Larson that on a cold start has good oil pressure but after about 15 minutes of running at about 3000 rpm oil pressure starts to drop(about 20 PSI at 3000 rpm not good need 10 PSI for each 1000 rpm) Pull throttle back to idle and 0 oil pressure.
Engine burns no oil
Engine has plenty of fresh oil
Engine has no bearing noise
Engine does have some lifter noise at 0 oil pressure
WHAT NEXT

SB,

First of all, there are several people on the Forum who have given sound marine engine advice and hopefully, they will participate in this as well. Having said that, it is my experience that what you are describing is not uncommon, at least for me, in that vintage of boats that I had. Depending on what type of engine you are describing, 4, 6, or 8 cylinder, and depending on your mechanical ability, the first thing I would do is remove the oil pressure sending unit and attach a manual oil pressure gauge ($10-$30 bucks on EBay)to the engine and perform the same test. Then you will know for sure by eliminating the sending unit and the dash gauge.
When a marine engine cranks out 3000 rpm it thins out the oil pretty good and then a sudden pull back of the throttle will give you a low oil pressure reading. For those of you reading this, try it sometime and watch your gauge, you'll be surprised.
There are many other factors such as the type and viscosity of the oil you are using, when it was last serviced, hours on the engine etc. I'm going to assume you take good care of your boat. The oil pressure test right at the block is a great way to start diagnosing. Hope this helps.

Blue Thunder

[robmac]

I agree with BT,start with simple and accurate tests. You can get a manual guage at Walmart or any local parts store for very little money. If you get the same results and the oil drain back passages on the top of the heads ( under valve covers are clear ) I think you'll find a dirty p/u or other pump issue. Hope it's just a bad sender but I'm not sure where at idle you are getting lifter noise which indicates lack of oil getting to them.

[ApS]

Originally Posted by Sunset Bob

"...Engine does have some lifter noise at 0 oil pressure..."

...Then your oil pressure gauge is definitely accurate at zero.

It's still possible that your sender couldn't take the pressure of this season's cold at your first start-up. (Pressure-senders made in China are problematic—and today, many are made in China).

In my engine, I'd suspect that a failed oil pressure relief poppet spring was letting the oil pressure drop; however, go back to when you last operated it:

1) What the last thing done mechanically to this engine before the problem surfaced?

2) Was the oil filter replaced?

Oil filters can have internal faults right out of the box: first change the sender, then do an oil filter change.

Both are quick and inexpensive diagnostics. Fill the filter with oil (or better, ATF) before installing it.

[Sunset Bob]

Thank you guys for your input.I will fool around with it next weekend.I think I have an oil pressure gage that I can try but with lifter noise I believe I do have an oil pressure problem.Pump or relief valve sound like good place to start.
BTW the engine is a V8 5.7 Mercruiser.
Thanks again and I will let you guys know what happens
Sunset Bob

[LIforrelaxin]

Originally Posted by Acres per Second

1) What the last thing done mechanically to this engine before the problem surfaced?

2) Was the oil filter replaced?

Oil filters can have internal faults right out of the box: first change the sender, then do an oil filter change.

Both are quick and inexpensive diagnostics. Fill the filter with oil (or better, ATF) before installing it.

APS, has the first two imediate questions right on the money....

the third question is did you do the last service on the boat or did a Marina.... I beleive a lot in self diagnosing and working on my own possessions. However if you had the boat winterized and the oil changed professionally at the end of last season, you need to have them look at the boat as soon as possible. The longer you work on diagnosing the problem, the less likely they are to take care of any error on their part.

[chunt]

If the lifters are tapping when the preasure goes low, then you do have oil pressure problems. How many hours on the motor? If the main and connecting bearings are worn, on the crank, then that would do exactly what you are describing. There is also another low pressure audible alarm sender on the motor. Is there an alarm noise? If you roll the thottle, raise and lower quickly a number of times, does the motor make a knocking noise. If it does, then the crank bearings are bad.

[Sunset Bob]

I was having the same problem the end of last season.Not to the extent of this spring.I was hoping that a new filter and fresh oil would help.
I am going to have the marina that winterized the boat last fall look at it. If it is an easy fix I will do that.But I can't see throwing a lot of money at a 12 year old engine.It may be time to repower or new boat.There may be some deals out there.

[trfour]

Bob, the lifter noise is a sign that there is a problem. 9 times out of 10, with an electrically gauged system its the sending unit or a bad connection in the wiring. As suggested a manual gauge would be the first thing to try.
Also I would recommend oil analysis to everyone, that can be set up through your oil supplier or dealer usually for free. Any abnormal bearing ware could be caught before you chuck a connecting rod through the hull and really get into trouble!
I'm hoping that the horse didn't get out of the barn with you, on this one!
T.

[Dave R]

Originally Posted by Sunset Bob

I was having the same problem the end of last season.Not to the extent of this spring.I was hoping that a new filter and fresh oil would help.
I am going to have the marina that winterized the boat last fall look at it. If it is an easy fix I will do that.But I can't see throwing a lot of money at a 12 year old engine.It may be time to repower or new boat.There may be some deals out there.

How many hours on the engine? Might just need new bearings and a fresh oil pump.

What kind of oil do you use? How often is it changed? What sort of cruising RPM do you typically maintain?

[Sunset Bob]

I don't have a hour meter but I use the boat a lot it really doesn't owe me anything.
Mercruiser oil every fall
Most of my cruising is done at 3000 to 3500 RPM
By GPS I put about 2500 miles a year on the boat.
I wouldn't be surprised if the bearings and oil pump are just worn out.
I think a new 350 mag would be nice.
A new boat would be nicer.
Gee come to think of it a little oil pressure would be nice.

[ApS]

Originally Posted by Sunset Bob

"...It may be time to repower..."

1) I quieted lifter noise (at start-up, anyway) by converting to Mobil-1 synthetic oil.

2) After doing the quick-and-cheap synthetic oil change, gauge check, and oil filter change, you might get another season out of it by adding Slick 50®, made by Quaker State.

3) Checking this BMW site promotes the same advice as above.

[LIforrelaxin]

Originally Posted by Acres per Second

1) I quieted lifter noise (at start-up, anyway) by converting to Mobil-1 synthetic oil.

2) After doing the quick-and-cheap synthetic oil change, gauge check, and oil filter change, you might get another season out of it by adding Slick 50®, made by Quaker State.

This my be all good if you have good oil pressure... and I wouldn't be surprised if it gave you a season or two.....

However Sunset here may have a oil pump issue.....and synthetics will not help that....

[Sunset Bob]

When I got to the lake I installed a mechanical oil pressure gage to confirm low oil pressure.I was getting 20-25lbs of oil pressure at 3000 rpm still not good.
Then I went out and got Mobil1 40 wt high mileage and slick 50 a new filter and did an oil change.This helped a little. I now have 25-28psi oil pressure at 3000 rpm.
I am know in the looking mode for a repower or new or used boat.

[ITD]

I don't know Bob, I think you will probably be ok for a while, as long as the lifters aren't clacking away at 3000 rpm. The spec for the motor is 30 psi at 2000 rpm according to this site http://www.perfprotech.com/store/art...fications.aspx

and 4 psi min at idle. I would probably avoid wide open operation, but I would run it until you let all the smoke out. Once the smoke is gone it's never the same. YMMV.

[ApS]

Originally Posted by ITD

"...The spec for the motor is 30 psi at 2000 rpm according to this site http://www.perfprotech.com/store/art...fications.aspx..."

Among other things, I found a Chevy spec that said 6 psi per 1000-RPMs was normal. (Not a Chevy person here).

Originally Posted by ITD

"...I would run it until you let all the smoke out..."

My criterion for a rebuild was when the engine knocked deeply at startup—then quieted.

"Letting the smoke out" was reserved for faults of the electrical system.

Originally Posted by Sunset Bob

"...a little oil pressure would be nice..."

Looks like you've got it.

Originally Posted by Sunset Bob

"...Then I went out and got Mobil1 40 wt high mileage and slick 50 a new filter and did an oil change.This helped a little.

Well, you did ask for a little oil pressure.

The lifters should be quiet at idle now, right?

Any foaming or air bubbles in the oil?

Is the dipstick the correct one for the engine?

I don't think what you have now is all that bad—you may be good for another season or two...it's a 12-year-old engine, is all. All my engines are older, and none have oil pressure gauges for a good reason.

[Dave R]

I'm wondering if your oil cooler is not operating properly.

Whatcha gonna do with the old engine if you re-power?

[Sunset Bob]

I don't have any lifter noise now at idle or at rpm.
Before the Mobil1 and slick 50 oil change I only had lifter noise at idle after the engine had been run hard.I am hoping that it will last the season and I will re power this winter.
If I buy a rebuilt motor they will probably take the old one as a core ti rebuild.If I buy new they probably won't take the old one in trade so I may have a very used 5.7 for sale.
I don't think this engine has an oil cooler so that is not the problem.

[jst_4_kiks]

Originally Posted by Sunset Bob

...I have a 5.7.
.....engine has an oil cooler

the 5.7 mercruiser engine is a very strong engine. if your engine has power steering (very likely) then you DO have an oil cooler. it is possible for the cooler tubes to be blocked with sludge and such.

to confirm that you have an oil cooler look down near the block on the port side of the engine. there would be a 3" by 14" (sizes vary) tube with the water inlet tube from the transom on one end and an outlet going to the engine. then on top of it there would be two hoses (in and out) for oil to cool. this oil cooler is usually supported by two hose clamps or some other type of brackets.

[Sunset Bob]

Originally Posted by jst_4_kiks

the 5.7 mercruiser engine is a very strong engine. if your engine has power steering (very likely) then you DO have an oil cooler. it is possible for the cooler tubes to be blocked with sludge and such.

to confirm that you have an oil cooler look down near the block on the port side of the engine. there would be a 3" by 14" (sizes vary) tube with the water inlet tube from the transom on one end and an outlet going to the engine. then on top of it there would be two hoses (in and out) for oil to cool. this oil cooler is usually supported by two hose clamps or some other type of brackets.

Thanks learn something new everyday.I will check this out next time up to the lake. I do remember seeing something like that and I do have power steering.

Too bad the Pontiac engine in my new avatar wont bolt in.

[VitaBene]

We can shoehorn that Pontiac motor into that boat of yours, a little welding and a few homemade adapters and you will be good to go!! What is that- 455?

[Blue Thunder]

Bob,

I agree with some of the recent posts. I don't think you have the big problem that you think you do. What you are describing for oil pressure is right where my 1985 Liberator 5.7 Mercruiser was for years. After I gave it a "hot supper", the lifters would clatter a bit too. Those Mercruiser Chevy 350's with 4 bolt mains are nearly bulletproof if you take care of them and it sounds like you do. It's your boat, do what you want but I don't think you need to repower it. JMHO.

BT

[Sunset Bob]

Originally Posted by VitaBene

We can shoehorn that Pontiac motor into that boat of yours, a little welding and a few homemade adapters and you will be good to go!! What is that- 455?

Yep a 455 punched .030 (462) solid lifter cam allunium rods lots of porting to the heads trick oil system 11.1 to 1 compression about 600 hp pushed my 74 bird to 11:50s at 118mph not a bad ride in the 80s.but to much work it was like a second job

[Sunset Bob]

Originally Posted by Blue Thunder

Bob,

I agree with some of the recent posts. I don't think you have the big problem that you think you do. What you are describing for oil pressure is right where my 1985 Liberator 5.7 Mercruiser was for years. After I gave it a "hot supper", the lifters would clatter a bit too. Those Mercruiser Chevy 350's with 4 bolt mains are nearly bulletproof if you take care of them and it sounds like you do. It's your boat, do what you want but I don't think you need to repower it. JMHO.

BT

Yes maybe I am a little to critical but its my nature.I am a FAA licensed aircraft mechanic.I am going to run the boat some more and see how it acts before I take out any guests.
And not like I want to spend the money but this boat will fly with a new Mag 350 OOOps there is that darn speed limit.

[VtSteve]

I had an 1994 Larson, small bowrider with the little puppy engine. Not sure I could have made it to the magical number. One thing to add. I have no idea if you've got an inclination to look around. But I've seen deals on new boats this year that really made me look seriously. My boat is an '06, so not great timing. But when I saw a pretty loaded Chap 250 cruiser going for $51 out the door? The used market is dead, even deader than the truck market. 2008 models are as cheap as new boats get.

[Winnipesaukee]

I'm what you call a "shadetree mechanic."

Here's what I think is going on.

In your crankcase, there is a spring-loaded piston that regulates oil pressure. Ideally, when the engine revs, this piston springs up, allowing the pressurized oil to bypass the "system" and redirect into/through the crankshaft, where it "seeps out" directly onto the crankshaft/conrod bearings. This action simultaneously regulates the oil pressure and lubricates these crucial bearings (keeping a film of oil between them and the crankshaft).

Every time you start your engine, these bearings wear a little more (get thinner) because there is no pressurized oil preventing them from touching (this is slightly different than "lubricating, where the parts actually touch"). Eventually, they wear so much that the space between the bearings and the crank grow so much that the oil "seeps" fast enough that the oil pump can't keep up.

This would fit your symptoms if the oil pressure relieve assembly (which I think Acres Per Second touched upon) or the spring was worn/damaged in a way that left it stuck open after running the engine for a period of time. This combined with the worn bearings would explain your problem.

One way to test it is to rev the engine (3000rpm) for a few seconds after the drop (do so at your own risk). If you get pressure again (pump is working harder at 3k than idle and may be able to overcome the extra volume loss), then I'm most likely right.

What can you do if that is the case? Run high viscosity oil. Viscous oil can't flow as fast and cannot "seep" past the crank bearings as fast. Try changing your oil with something like 20w-50 and that will extend the life of the engine a bit.

Oh, and get Seatow.

Hope that helps a bit. Best of luck. If you have any questions, post it up here or PM me.

[trfour]

Originally Posted by Sunset Bob

Yep a 455 punched .030 (462) solid lifter cam allunium rods lots of porting to the heads trick oil system 11.1 to 1 compression about 600 hp pushed my 74 bird to 11:50s at 118mph not a bad ride in the 80s.but to much work it was like a second job

No wonder I like you! I ran a 58 Corvette back in the 60's, C/Gas and ran on the National record at New England Drag way, Sanford ME. 10.20000
Like you, when the fun came abruptly to a halt when they started bracket racing, kind of took all of the fun out of it. I had a 1959 F150 with a tricked 460 cu inch engine that we could have had fun racing. "LittleFoot' would scat too!
Terry

[Sunset Bob]

OK after running the boat this weekend and looking at new boats my old Larson is going to make the season.Sat I did a cruise around Long Island and today I took a cruise up to Moultonborough bay Poplar Island to see the eagles.The boat ran fine and as long as I don't look at the oil pressure gage I would never know it is a little low.I am getting about 25psi at 3000 rpm and about 6psi idle with no lifter noise.

[Just Sold]

Bob, If you now have the oil pressure you stated you should have nothing to worry about for this season. APS's suggestion of Mobil 1 and Slick 50 were excellent. Just keep and eye out to make sure the crankcase is full before each trip out on the lake. I also know that you never have beat on your boat so abuse was never a concern.

[macshpman]

I would have to say that if you ran that vette you must know some of the same racers I do. Doug Jounis must come right to the forefront as he also ran a corvette in that time frame. How about Phil Miller, Smiley Smullens, Ray Blake, Art Gallent, Bill Douglas and I am sure that you can name a few others. Also Sunset Bob you should a good oil in that engine that still has a high concentrate of Zinc and Phosporus. Brad Penn SAE 40 or SAE 50 would do the trick as you are more concerned with oil pressure and protection then gas mileage. You did mention that the oil pressure drops after a hard run which would suggest that it may be a temperature related problem. As oil increases in temp it thins and builds less pressure. Could it be an oil cooler that is losing its ability to cool the oil. That coupled with wear on the engine over the years could be causing the problem. Just a thought.

[robmac]

And don't forget Ron Keenan (Mr Boston TF) Billy Pike, Dick Ingalls oh the list is long. They all helped me get started, as well as Tony Grasso

[VitaBene]

Originally Posted by Sunset Bob

Yep a 455 punched .030 (462) solid lifter cam allunium rods lots of porting to the heads trick oil system 11.1 to 1 compression about 600 hp pushed my 74 bird to 11:50s at 118mph not a bad ride in the 80s.but to much work it was like a second job

I have a 70 Olds with a 455 punched to the same size. Did it up streetable with Mondello parts and pieces including adj valvetrain, had him port my cast heads. I need to git er dun