Unusual oil consumption? VP GM V8 Vortec 5.7

[Danmarine]

Hello everyone.

I have an acquaintance who has struggled for a long time to get his engine and boat working properly.
The short of the long story is that they had the old engine removed as it was defective.
A brand new Vortec 350/5.7 V 8 was bought home, replaced with the necessary parts and whatever else was needed and had it installed.

It runs super fine and everything is as it should be.... Apart from him mentioning something about it using an extreme amount of oil??
But there is nothing to see in the exhaust smoke or in the pipes and not immediately on the spark plugs either?

A certain oil was poured in from the start by the mechanic and some time later the owner himself changed the oil with a 15w50 - is it possible that the oil is too thin and therefore makes it easier to get between the piston rings and in the combustion? But still only so little that it can't really be seen?

It all came about because the low oil pressure light came on and therefore he decided to change the oil because the mechanic said it would be sensible to change the oil after some time with the break-in. When draining the oil on the engine, no more than just under 2 L could be drained - despite the manual saying it should use 4.7 L (5 qts) without filter or 5.6 L (6 qts) with filter....

At the start, when running in the engine, there will probably be an extra consumption. But do you have any experience of how much?

According to the owner, there is NO leakage and no blue or black smoke - but the oil must end somewhere... And there is no oil film on the water either?

Has anyone experienced anything similar or heard of something similar?

Hoping for a quick and effective treatment of the problem, otherwise it may turn out to be another long and miserable period for him.

Great day to all of u'

 

[alldodge]

There are many configurations of the 350, have a serial number for the original motor?
Does the motor have a oil cooler?

 

[Scott06]

When u say brand new was it a new gm base engine or remanufactured ?

Was the engine to properly broken in by varying the rpms for First ten hours of use ? This is done to seat the rings

Michigan motorz recommended I use rotella conventional oil for break in and not use synthetic until the engine had 100 hrs

So he went though three or four qts of oil ? That does seem excessive if accurate I would be contacting the engine supplier as it could be defective

 

[Danmarine]

Hi Alldodge & Scott06

Yes, of course there are many models. The best information we have been able to gather at the moment is:

BRAND NEW Chevrolet Performance 350/5.7 V8 model Vortec 1996 - 2002 (Enginee 12530283 12681431) Why there are 2 numbers I don't know?

Another document that came with the engine is this: Part number 12681431 5.7 L Engine is a L31 H.D. Engine.

The engine has been properly run-in and there is nothing else to see or hear. Now I was out there myself and looked under and while it was running - it is in the water.
The engine runs super fine, sounds healthy and strong. The oil pressure is up to 4 bar (sounds a bit high, but according to the manual and paper it is correct enough, at revolutions)

There is no smoke at all, no leakage to be seen.... It is quite strange.

I drove home again and in the meantime the owner just wanted to sail for a little while he kept an eye on the oil pressure and alarm.
He barely makes it out of the harbor and the oil pressure drops to 1 bar - turns off the engine and has the boat towed back home. After a while he checks the oil level and the oil is gone???

No oil stains in the water, no leaks, etc.
In the end, the oil has to end up somewhere, but do you think it almost has to end up in the combustion? It may eat very little at a time. But normally I think you can see it.

In addition, I thought about whether the oil pump has a safety valve that opens when the pressure is incorrect - but therefore the oil should not disappear

The engine does not have an oil cooler.

I think this could turn into a long and boring task with complaints etc

 

[Scott06]

Hi Alldodge & Scott06

Yes, of course there are many models. The best information we have been able to gather at the moment is:

BRAND NEW Chevrolet Performance 350/5.7 V8 model Vortec 1996 - 2002 (Enginee 12530283 12681431) Why there are 2 numbers I don't know?

Another document that came with the engine is this: Part number 12681431 5.7 L Engine is a L31 H.D. Engine.

The engine has been properly run-in and there is nothing else to see or hear. Now I was out there myself and looked under and while it was running - it is in the water.
The engine runs super fine, sounds healthy and strong. The oil pressure is up to 4 bar (sounds a bit high, but according to the manual and paper it is correct enough, at revolutions)

There is no smoke at all, no leakage to be seen.... It is quite strange.

I drove home again and in the meantime the owner just wanted to sail for a little while he kept an eye on the oil pressure and alarm.
He barely makes it out of the harbor and the oil pressure drops to 1 bar - turns off the engine and has the boat towed back home. After a while he checks the oil level and the oil is gone???

No oil stains in the water, no leaks, etc.
In the end, the oil has to end up somewhere, but do you think it almost has to end up in the combustion? It may eat very little at a time. But normally I think you can see it.

In addition, I thought about whether the oil pump has a safety valve that opens when the pressure is incorrect - but therefore the oil should not disappear

The engine does not have an oil cooler.

I think this could turn into a long and boring task with complaints etc

What do spark plugs look like wondering if I take gasket isn’t on correctly and sucking oil into intake port via lifter valley ?

 

[Lou C]

Agreed if oil is burning you’d think you’d see it on the center electrodes of the spark plugs. So it’s starts out OK with 4 bar oil pressure (~~58 psi which is fine) but then the oil pressure drops and you find that the engine is very low on oil. I would do a compression & leakdown test even though it was a new engine to start. I bet if the boat was pulled out and run on the water muffs on land you’d see some sign of smoking. That can be hard to see with under water exhaust. I’m thinking it’s possible piston rings were installed wrong or valve seals are leaking oil back into the cyls. Also might want to put dye in the oil & really check it well with a black light for leaks….

 

[alldodge]

Does the motor have a oil cooler?

Is there a oil cooler

 

[Lou C]

He said it doesn't. Too bad that would have been an easy fix!
Normally on small block Chevrolets even with an old engine with tons of hrs on the short block like mine they will be at least at 20 psi at slow idle (600 rpm) with a hot engine even after coming off plane. Over 800 rpm I am back up to 40 psi and over 2000 about 55 psi.
I do run Mercruiser/Quicksilver 25/40 oil, you can also use straight 30 or 40.

 

[QBhoy]

Hi. 4 bar is nearly 60 psi. You think it’s this high when it’s running under normal conditions and warmed up ? If so…I’d say that gm will have a hard time containing that kind of pressure for too long at any sort of higher rpms. Something gotta give. Is it likely she’s running cold, she’s blocked up somewhere or perhaps there’s an oil cooler issue ?

 

[Lou C]

Mine has always run that pressure (approx 60 psi) with the boat up on plane, 3200-3600 rpm let’s say. Never had a problem!

 

[QBhoy]

Mine has always run that pressure (approx 60 psi) with the boat up on plane, 3200-3600 rpm let’s say. Never had a problem!

Hi Lou. I’d hazard a guess that your gauge is optimistic for sure. No way you should be at 60 psi on a gm under normal conditions and warmed up. Not saying it’s detrimental…but very unlikely to be a genuine reading at that.
But to be fair. The shop manual for these also suggests that the minimum oil pressure acceptable is as low as 4 psi. Jeez…if mine dropped anything below 25/30…I’d be shutting down and calling a friend for a tow .

 

[Lou C]

I'm thinking that some of the variance in these is because of difference in the pressure relief valve & spring in addition to the gauges not being 100% accurate. Perusing some owners forums of S-10 trucks that all used the 4.3 which is very similar to the 5.7 they report 60 at speed, 40 at moderate speeds and 20/25 at hot slow idle which is what I'm seeing.
Then again my '98 Jeep 4.0 inline six is at 40 most times, with a high of 50 psi and a low of 30 psi at idle. That's at 24 years old and 180,000 miles.
I'm actually pleased to see my boat being as high as it is, seeing as how back in 2016 the engine blew both head gaskets, had salt water in the oil for approx 3 days to a week before I figured out what was wrong and got it all out. I replaced the old heads but didn't know if the bearings were damaged by the water in the oil till I ran it after repairs. Five years later still good so I guess I got lucky!

 

[Danmarine]

Hello everyone.

Thanks for all the hints and tips

As mentioned, the engine ran super fine and everything was as it should be. 45-60 min operation and the owner chooses to sail out for a trip. Not much later, the oil pressure dropped immediately and he subsequently could not measure any oil level on the engine - even the next day he could not measure any oil level, so the oil is gone.

45-60 min. the oil cannot be measured - this corresponds to approximately 2-2.5 liters of oil that has disappeared!
I agree that it is not always easy to see the color of the smoke or similar. when the exhaust is under water. But with such a large consumption, in such a short time, I would think there would almost be a lake of oil after the boat?
In addition, I would also think that the engine would run badly, which it does not.

He has also checked the spark plugs and there is nothing wrong with them either.

From there I can't say much more. Now we have to get the boat up next week and then the engine will be completely cleaned also under and around it.
Then we have to fill up with oil again and see how it is when you test it on land.

I cannot rule out that there is a leak on the engine somewhere or whether it is a sensor error - as well as a bad dip-stick controle of oil

I will write when I know a little more.

Good day to you