1992 Mercruiser 454 low oil pressure

[mick3447]

I just bought a 1992 Sea Ray 350 Express Bridge with twin 454 Mercruisers 7.4L. On the sea trial, both engines ran great with oil pressure in 40 to 60 psi range depending on RPMs; after I bought the boat, I started it up to take it out, and the port engine low oil pressure alarm went off and the gage showed less than 5psi. I checked the sending unit, and it pegs out when grounded; the oil level was perfect but dirty. I flushed and changed the oil and filter and I am getting 40+ PSI at startup and it drops to 20 PSI once warmed up. When I rev up the RPMs the pressure increase back to 60 PSI until I get over 3000 RPMs then it drops to +/- 10 PSI. When I reduce the RPMs the pressure comes back to 40ish PSI and stays steady. Is this an oil pump failing or some other problem? There is no noise coming from the engine, only when the pressure dropped when I first had the problem the values made noise. They make a little noise now at cold startup but quite once the engine has run for a few seconds. I put a mechanical gauge on it and get the same results.

 

[alldodge]

Is this an oil pump failing or some other problem?

Howdy
Lets start off with what is the motor serial number?

My first thought is its the gauge or the sender. An issue with that is the alarm going off with low pressure, being the gauge sender and alarm sender are normally different (having S/N of motor will verify)

Get a mechanical pressure gauge or rent one from a local auto parts store. Connect it where the gauge sender is. Run motor and see if same thing happens

Check oil level again to make sure it remains constant

 

[Scott Danforth]

exactly, get a mechanical pressure gauge and verify what you have.

 

[mick3447]

Howdy
Lets start off with what is the motor serial number?

My first thought is its the gauge or the sender. An issue with that is the alarm going off with low pressure, being the gauge sender and alarm sender are normally different (having S/N of motor will verify)

Get a mechanical pressure gauge or rent one from a local auto parts store. Connect it where the gauge sender is. Run motor and see if same thing happens

Check oil level again to make sure it remains constant

There are no serial numbers on these engines, I’ve looked and my mechanic has looked. They are after market motors. I believe they are 1992 to 1994 in year but have been rebuilt, the oil pan looks different and value covers are not marine type. My mechanic has put a mechanical gauge on the motor and he is getting the same results as I described in my first post. He say that it’s either bearing clearance or the oil pump. Obviously there is a different cost for the different problem. I was hoping that someone on this forum might’ve had a similar problem and could guide me in the right direction.

 

[Scott Danforth]

1992 could be a left over Mk4 motor or a Gen-5. the 1994 would be a gen-5

if you dont have a serial number, post the casting numbers of the blocks and heads.

the fact that your oil pressure is dropping with a mechanical gauge means the motor is coming out and you are putting it on a stand and tearing into it.

 

[alldodge]

Agree, need to pull the motor