Correct oil pressure?

[Misty IV]

My Islander has the 4.3L MerCruiser with about 225 hours on her (new engine in 2005). My question relates to the oil pressure. When the engine is running, the oil pressure stays the same on the in-dash gauge, around 80psi. It doesn't change between idle or full throttle. I know the pressure shouldn't stay the same throughout the RPM range, should it? The engine purrs like a kitten, doesn't overheat, so I know it's getting oil. Any ideas about the steady pressure and what it should be through the RPM range? The wire is connected to the oil pressure switch on the engine and to the back of the gauge in the dash. I'm using the MerCruiser 25W-40 oil.

[W.W.IV.]

Misty,I'm driving a 97 chevy pickup with the 4.3 v6, its pushing 170k miles has all ways held 70lbs of oil pressure. I've only seen it drop to 40psi. about twice. I run 10w30 in the truck. That 25w40 your using will keep your pressure up at low RPMs 600. If you want to see the gage move switch to 5w30.My Baha had twin 305 v8s and if I dropped down to 600rpm it would lose oil pressure, I switched oil to 20w40 and it never went bellow 40lbs psi. Hope this helps.

[landingzone]

Oil pressure sounds too high. I'm not an expert, but my shop manual says 30-55 psi at 2000 RPM for that engine. Maybe your gauge isn't telling the truth.

Dick

[L&M]

With the weight oil your using and a high volume oil pump that was probably used in the rebuild. 80psi is not out of the ordinary. I would run a manual test gauge right at the engine just to verify what your dash gauge is telling you and how accurate it really is at lower rpms.

[Misty IV]

Hank, I was actually thinking about doing a pressure test at the engine after I originally posted to rule out the sending unit and/or the gauge. Good advice! I thought about changing to a different grade oil, but my manual specifically calls for the 25W-40, so feel I should stick with it, unless anyone feels it isn't necessary. The engine sees a lot of trolling time, especially when the winds come around and the kicker can't hold course anymore.

[fish-on]

Hi, i had the same problem with my islander too. Might sound crazy but when i bought the boat , the motor had a fram oil filter on it, It would idle at 60 psi, A buddy of mine at work is a boat mechanic, has been for over 20 years, We changed the oil and filter, put 25/40 in it, we put a mercruiser oil filter on, It changed instantly, 35 idle- 65 wide open. He said the reason why was because the fram filter constricts the oil flow to much, He told me not to ever run an automotive filter again! He said mercruiser filters were made not to restrict the flow like auto filters, for the purpose of trolling and keeps the engine cooler. ALSO he said the people that run the auto filters beware, The boats that run them tend to start running alittle hotter over time, and that causes oil slugde build up in the oil pan, you know whats next, plugged oil pump, blown motor.

[Misty IV]

Hi, i had the same problem with my islander too. Might sound crazy but when i bought the boat , the motor had a fram oil filter on it, It would idle at 60 psi, A buddy of mine at work is a boat mechanic, has been for over 20 years, We changed the oil and filter, put 25/40 in it, we put a mercruiser oil filter on, It changed instantly, 35 idle- 65 wide open. He said the reason why was because the fram filter constricts the oil flow to much, He told me not to ever run an automotive filter again! He said mercruiser filters were made not to restrict the flow like auto filters, for the purpose of trolling and keeps the engine cooler. ALSO he said the people that run the auto filters beware, The boats that run them tend to start running alittle hotter over time, and that causes oil slugde build up in the oil pan, you know whats next, plugged oil pump, blown motor.

I wonder if that is my problem, too. I have been using a Purolator oil filter. I've seen the MerCruiser filter and noticed it wasn't as long as the Purolator. I just changed the oil in the fall before winterizing the boat. Maybe I'll also try the Merc filter if the manual pressure test that Hank suggested I do doesn't change things. Good point, fish-on!!!

[L&M]

Very good point on Fram whether it be marine or automotive.

[fish-on]

Did your boat do it before you changed the oil?

[Misty IV]

Did your boat do it before you changed the oil?

Yes, it's always been on the high side. When the engine starts, it jumps up to about 50psi, then rises and steadies-out around the 80psi mark. I've always used the Purolator filter when I change the oil 2x each year. Wasn't until lately that I thought about the high pressure and got curious. Never had any issues with the engine or excessive usage, so didn't think much of it.

[fish-on]

You had the engine rebuilt, probably high volume oil pump, or did somebody stretch the spring in the oil pump? That will cause the high oil pressure. It looks high on the gauge but it's realy not at all in the motor. should'nt hurt anything. But i'd still do a pressure check to be sure.

[Misty IV]

You had the engine rebuilt, probably high volume oil pump, or did somebody stretch the spring in the oil pump? That will cause the high oil pressure. It looks high on the gauge but it's realy not at all in the motor. should'nt hurt anything. But i'd still do a pressure check to be sure.

When I bought the boat in 2005, it had a fresh engine and outdrive on it. The previous owner didn't winterize the engine or outdrive in 2004 and the engine block cracked, as did the outdrive case. When I bought the boat, the combo had 10 hours on it. He didn't have any paperwork on the rebuild, other than it was a Jasper engine.