Mercruiser 7.4 MPI - Correct Oil pressure readings - Help please.

[jezzb]

Hi All,

I just overhauled my engine - it's a Mercruiser 7.4 MPI from 1998 - serial 0L314***. I have new main bearings, new connecting rod bearings, new oil pump, new oil switch and skimmed crank, new pistons, new rings etc. I wish to know which oil pressure readings I should have on idling and at let's say 3400 revs (whilst under way at sea).

On the engine specifications it says that I should have between 30 and 7- psi. Should I have 70 psi as everything is new? My current reading is 40 psi - on idling or under way. After a long drive is goes down to 30 psi.

Thanks in advace for any help.
Jesmond

 

[Fun Times]

Re: Mercruiser 7.4 MPI - Correct Oil pressure readings - Help please.

I found some engine spec's for you to take a look at, This should help you out a little bit here. See page 1B-4

Oh sorry about that, I see you already had this info.:redface:
http://www.boatfix.com/merc/Servmanl/16/16B1R2.PDF

 

[Bondo]

Re: Mercruiser 7.4 MPI - Correct Oil pressure readings - Help please.

Ayuh,... The ole Rule of Thumb is 10psi per 1000rpms.....

 

[Don S]

Re: Mercruiser 7.4 MPI - Correct Oil pressure readings - Help please.

The first thing you should do is install a mechanical guage to the engine and run it to verify the actual oil pressure. You could have a faulty sender or gauge.

 

[jezzb]

Re: Mercruiser 7.4 MPI - Correct Oil pressure readings - Help please.

Thanks for all you replies.

I have forwarded all your replies to my mechanic.

I also found out that my mechanic did not change the Main Bearing cap bolts and the Cylinder head bolts. Can someone please send me some information from where I can buy theses especially the Main BEaring Cap bolts as I cannot find them as I do not know that part number. Even the part numbers and quantity needed would help. I am looking for OEM parts.

Thanks in advance
Jezz

 

[Bt Doctur]

Re: Mercruiser 7.4 MPI - Correct Oil pressure readings - Help please.

Wouldn`t worry about the bolts now that it`s running.

 

[Fireman431]

Re: Mercruiser 7.4 MPI - Correct Oil pressure readings - Help please.

I have 2 7.4L MPI's (2001) with 350 hours on them.

Engine 1) Cold - 40 PSI; Warm - 30 PSI
Engine 2) Cold - 38 PSI; Warm - 22 PSI

Both engines are as delivered from the factory. Nothing more than routine maintenance & fluid changes.

 

[Fireman431]

Re: Mercruiser 7.4 MPI - Correct Oil pressure readings - Help please.

Forgot...both engines are at 36 PSI (warm) at 3500 RPM.

 

[Don S]

Re: Mercruiser 7.4 MPI - Correct Oil pressure readings - Help please.

I also found out that my mechanic did not change the Main Bearing cap bolts and the Cylinder head bolts.

It's not requiered by GM, or Mercruiser to replace the head and main bearing bolts at rebuild. It's fine to replace them if you want to just throw money at something, but not something that is done on any kind of standard rebuild that I know of on Chevy SB and BB engines. So don't blame your mechanic for not doing it.
Any Chevy or GM dealer can get you head and main bolts if you WANT them. They are not a marine specific part.

 

[Bondo]

Re: Mercruiser 7.4 MPI - Correct Oil pressure readings - Help please.

Forgot...both engines are at 36 PSI (warm) at 3500 RPM.

Ayuh,... The ole Rule of Thumb is 10psi per 1000rpms.....

Ayuh,..... So what's the Problem,..??

 

[Fireman431]

Re: Mercruiser 7.4 MPI - Correct Oil pressure readings - Help please.

No problems with mine. The OP was wondering what his pressure should be underway and it sounded like he was looking for ~40 psi. I was just giving him a little comparison.

 

[Don S]

Re: Mercruiser 7.4 MPI - Correct Oil pressure readings - Help please.

No problems with mine. The OP was wondering what his pressure should be underway and it sounded like he was looking for ~40 psi. I was just giving him a little comparison.

Yes, but that was way back in December.

Thread closed