Mercruiser power loss with low oil pressure

[riviera man]

I have a 40 foot 2002 Riviera (Australian boat) M370 with two 5.7 litre 300 hp fuel injected stern drive inboard mercruisers. While cruising along at 3600 rpm, one engine suddenly went to idle and then quit. Oil level checked and seemed OK. Boat serviced 3 months ago. The engine felt hotter to the touch than the good one and showed a higher, but still reasonable cylinder head temp reading than the good engine. This may just be because it shut down 10 minutes before and gets temporarily hotter without cooling water flow.
Dived under and checked prop clear and cooling inlets not blocked.
After a half hour cooling period, started both engines OK and moved off at brisk idle of 1500 rpm with no problems. However, on opening up to cruise rpm the engine again went to idle, rpm fluctuated briefly then went to zero.
I noticed the oil pressure was reading some pressure, but way lower than the good engine. So came home on the good engine only. Checking next day, motor idles perfectly with all oil and temperature parameters normal.
There is absolutely no oil around the engine or in the bilge. Checking the dipstick showed correct level and no sign of water ingestion into the oil system. Could this be an oil pressure sensor fault and is there inbuilt protection which takes power off the engine in case of genuine oil pressure problems? Or could it be something else which cuts back power for some reason, for example a fuel control unit?

 

[Don S]

Re: Mercruiser power loss with low oil pressure

Check the oil level after has been shut off for a while. If it's over full, it could cause that problem. You really don't want to be over the full mark. The crankshaft will hit the oil, aireate it and cause the lifters to become soft which causes misses. Also, the oil pressure switch for the ECM will see low pressure and drop the rpm, but with soft lifters, it will probably stall the engine.
All because the engine has TOO MUCH oil.

 

[abj87]

Re: Mercruiser power loss with low oil pressure

Have you verified the oil pressure with a shop mechanical gauge?

 

[chiefalen]

Re: Mercruiser power loss with low oil pressure

Have you checked to see if something got sucked up and is blocking your t-stat.

Or when was the last time you pulled the risers on that motor.

You have a heat exchanger on that motor?

Common for that to get clogged up.

You do have some kind of raw water impeller, when was that changed last ?

 

[newport dave]

Re: Mercruiser power loss with low oil pressure

What is happening is your "Engine Gaurdian" system is being activated.

To explain, those engines have a Engine Gaurdian system that reduces The available power and can even shut the engine down when a critical situation emerges. It also records when and why they happened.

So, the good news is you don't have to guess why the engine shut down.The bad news is that you have to have a scan tool to access this information. The other reason for concern is you should have had an audio alarm when this occured, so you need to find out why that didn't happen.

 

[180shabah]

Re: Mercruiser power loss with low oil pressure

I;m with Don on this one - immediately after the incedent there was low oil pressure indicated on the gauge, but after sitting overnight and cooling off, pressure was right back where it should be.

Check oil level before running the engine.

 

[chiefalen]

Re: Mercruiser power loss with low oil pressure

There is no water in the oil is there, raising the oil level, causing the motor to shut down.

Hope not. You don't see alot of steam coming into the carb from the manifold hose.

Hope not. Would indicate the riser or manifold is leaking into a cylinder.

Gas you wouldn't see in the oil would smell it though.

 

[newport dave]

Re: Mercruiser power loss with low oil pressure

There is no water in the oil is there, raising the oil level, causing the motor to shut down.

Hope not. You don't see alot of steam coming into the carb from the manifold hose.

Hope not. Would indicate the riser or manifold is leaking into a cylinder.

Gas you wouldn't see in the oil would smell it though.

Chiefalen,
Sorry to lash out at you, I sure you're a great guy, but must you post on EVERY thread?

The engine(s) being discussed here are computer contolled multi-port fuel injected engines. Seeing as you referenced a "carb", it's appearent that you are not aware of that and have no expierence to base any qualifed suggestions here. Your ponderings only serve to dilute and obscure information that is relevent to the original poster. Again, sorry, I'm sure you intend to help, but enough is enough.

Dave

 

[chiefalen]

Re: Mercruiser power loss with low oil pressure

Of course Newport i won't post to this thread anymore.

I am not qualified to reply to a fuel injected question.

Nor anything mechanical that has a computer in it.

In your opinion that is.

But cause it's your opinion doesn't make it a fact.

And further more, i have no desire to prove my qualifications to you, now or in the future.

And i also, request the mods to leave up his last post to the thread.

And no action be taken against him in any manner.

Thank you !

 

[KJSmitty]

Re: Mercruiser power loss with low oil pressure

Checking the dipstick showed correct level and no sign of water ingestion into the oil system. Could this be an oil pressure sensor fault and is there inbuilt protection which takes power off the engine in case of genuine oil pressure problems? Or could it be something else which cuts back power for some reason, for example a fuel control unit?

I believe your question above will be your answer. I would have the system checked/diagnosed for "faults" as Dave mentioned above.
- Can you reproduce the event/oil pressure drop if rev'd to 2500 or so in neutral?

 

[riviera man]

Re: Mercruiser power loss with low oil pressure

I believe your question above will be your answer. I would have the system checked/diagnosed for "faults" as Dave mentioned above.
- Can you reproduce the event/oil pressure drop if rev'd to 2500 or so in neutral?

Thanks everyone for their input. I ran both motors in neutral at 2700 rpm for some time and the motor did not shut down, but of course it was not under load. At that power setting, the good motor was 60 psi oil pressure and the suspect motor was 43 psi, so there is quite a difference under the higher throttle setting. I could not detect much difference when just running both at idle for comparison purposes.
I don't think its a cooling problem, for example corroded manifolds or risers, as the cyl head temp stayed perfectly normal.
I also don't think its an over full problem either, as its just at the top of the range on the dipstick and the boat has done literally hundreds of miles since the last oil fill 3 months ago.
So I feel it all comes back to a low oil pressure, whether real or a faulty guage.
So I am taking your advice and getting a diagnostic done next week and will post the results so you can compare with your posted suggestions. Thanks again.

 

[riviera man]

Re: Mercruiser power loss with low oil pressure

Well the oil pressure guage is just a little inaccurate so that was a red herring. A diagnostic showed that it is the water pressure sensor sending a false signal. The engine Guardian function shut down the motor as a precaution. Apparently it is hard to do much harm these days to a Mercruiser as it is so well protected. They have come a long way from a fresh water lakes engine to a world wide salt water engine. The water sensor failure was due to electrolysis caused by the reaction of some carbon lining in the sensor and the metal in the sensor. It is so common that the mechanic always carries spares in his van. Problem fixed. Thanks for everyones input.