Mercruiser exhaust question

[finaticmw]

I have a strange one. I have a 2009 Mercruiser 5.0 mpi and it drives a bravo 3 dual prop out drive on my 25ft cruiser. It recently had a major cooling system overhaul which included the out drive being removed. Today I had it out for the first time. At speed (4000 rpm) the boat has a normal noise level that gets loader for about 8 seconds then goes back to normal for about 15 seconds the starts all over. It seems to do this no matter what engine RPM I'm running at. It almost sounds like the load on the motor increases but there is no change in speed or RPM when this happens. I checked the out drive oil reservoir that is mounted to the engine and it was basically empty. I could see the sensor at the bottom however there were no alarms. Anyone ever had this happen to them?

 

[Bondo]

I checked the out drive oil reservoir that is mounted to the engine and it was basically empty. I could see the sensor at the bottom however there were no alarms.

Ayuh,...... alarms don't always work,.... get it filled up / checked out before you run it again,....

 

[alldodge]

^^^Agree
Wouldn't be the first time someone forgot to fill the bottle, or "more" importantly the drive was not filled correctly, or you have a leak

With drive all the way down on a trailer, remove the upper vent screw, you should see greenish color gear lube come out.

 

[Lou C]

I change the oil in my brothers Merc Alpha with the bottle and what I found was you have full it till it comes out the vent, then replace vent screw and keep pumping till the gear oil reaches the lube monitor bottle. Since there could be air pockets you have to recheck it after running it the first time right after a gear oil change. After that the level shouldn’t change much…

 

[finaticmw]

Do you guys think this out drive oil issue could cause the strange exhaust sounds I reported?

 

[alldodge]

Anything is possible, but being at 4k rpm it might be the ECM cutting back power from a knock or something else

 

[tank1949]

Do you guys think this out drive oil issue could cause the strange exhaust sounds I reported?

I liked to have never secured my exhaust bellows on Alpha and Bravo 1. I am not familiar with III. Raise OD and see if noise is also coming from leakage.

 

[Stinnett21]

Do you mean you had it out for the first time after the cooling system overhaul? Describe the cooling system overhaul. What was done?

 

[finaticmw]

Do you mean you had it out for the first time after the cooling system overhaul? Describe the cooling system overhaul. What was done?

Everything was done. Three different mechanics including the dealer. It included the manifolds, risers, elbows, thermostat housing and thermostat, new raw water pump, new manifold ball valves, new cool fuel unit, every line was removed and flushed (there were several old impeller pieces in the system). He removed the out drive as there was no water coming out as normal. The cooling system works great now. He says that all the bellows and u joints were looking good.

 

[Stinnett21]

A video/audio would help.

 

[Scott06]

Everything was done. Three different mechanics including the dealer. It included the manifolds, risers, elbows, thermostat housing and thermostat, new raw water pump, new manifold ball valves, new cool fuel unit, every line was removed and flushed (there were several old impeller pieces in the system). He removed the out drive as there was no water coming out as normal. The cooling system works great now. He says that all the bellows and u joints were looking good.

Would check the flame arrestor is on tight and the exhaust bellows are not torn or off. If i recall on the mpi there are three studs or shoulder bolts that hold on the flame arrestor and cover that are kind of a pain to get off ?

 

[Stinnett21]

My MPI has the three studs and nylon lock nuts 10mm that hold it tight. They are very easy to get on/off. That's a great thought tho Scott. Hadn't thought of something like that. My only other thought is some kind of ventilation going on.

 

[finaticmw]

I reached out to my mechanic about this. He is going to go back abound what he touched to make sure all is AOK. The speedo isn't working now either. I think it's a petit tube issue since it was fine before the out drive removal. You guys mention the flame arrestor. We are talking about the air intake correct? As far as I know he didn't mess with this during the repair.

 

[04fxdwgi25]

Common overlooked item is plugging the pitot tube back into the lower drive on assembly

 

[finaticmw]

Common overlooked item is plugging the pitot tube back into the lower drive on assembly

That's what I thought. Does the drive have to come off to plug it back in? It's a Bravo 3

 

[04fxdwgi25]

No. With drive tilted up, it is easily reached at the top of leading edge of the lower unit. A yellow connector.