Oil pressure regulator

[cprbr]

My Mercruiser 5.7 developed an oil pressure problem. It was holding at 40 psi hot, cold, idle, or cruising. Suddenly, it idles at 20 psi, and tops at 70 psi at 3,000 rpm. I think the pressure relief valve is stuck, but i don't know where it is, or how to take it out and fix it. Any help?

I also have a heating problem that began about the same time. I got into some sea weed in Puget Sound and the motor over heated. After clearing the seaweed, the engine continued to have a heating problem, so I replaced the thermostat (160). Now it heats up to 190 and holds. Problems may be unrelated, but maybe someone else may find a coorelation. Let me know here or at my e-mail: EDIT

 

[HHIBouy]

Re: Oil pressure regulator

To my knowledge there is no pressure regulator on your engine. There is a oil pressure sender that sends info to your gauge. Pressure is developed by the oil pump inside of the engine.

Just my thoughts, but I would think that your over heating and oil pressure problems are related. I'm sure some of the gurus here will have a starting point, but my guess is you have blown some gaskets. The first that come to mind would be the head gaskets.

 

[Don S]

Re: Oil pressure regulator

Does this 5.7 Mercruiser have a year?
Is it raw water cooled or do you have a heat exchanger?

 

[zbnutcase]

Re: Oil pressure regulator

The pressure relief valve is built into the oil pump inside the pan. Have never seen one stick, but have seen the pin that holds it in fall out causing ZERO oil pressure.

 

[Bifflefan]

Re: Oil pressure regulator

Have never seen one stick, but have seen the pin that holds it in fall out causing ZERO oil pressure.

They can stick, but it is usually in an engine with 150,000 miles and still has the original oil in it.
Also if it was stuck open you would probably not have any pressure at an idle.
I would check the oil psi with a mechanical gauge and see what it says first.

As for the running hot, that depends on it you have a raw water or heat exchanger system. But it could be a worn impeller on both systems.

 

[HHIBouy]

Re: Oil pressure regulator

Well it just goes to show that even an old dog can learn new things. Did not know the pump had a pressure regulator built in it.:redface:

 

[cprbr]

Re: Oil pressure regulator

Thaks to all for your comments. Here are a few more clues:

I changed the raw water pump this season because last year I got into some sea weed, and over-heated the motor. The pump is on the motor (and a real pain to repair), and the a plastic housing was burned inside. So a new impeller and housing.

It is fresh water cooled, and I opened the exchanger, but no debris inside. My next plan is to back-flush the water intake back out the outdrive and see if there is any debris or obstruction. Then I'll start it and watch to see if it comes up to 160 degrees. It might hold there while the thermostat opens and uses the coolent from the exchanger, and then go on up, or it might just move on up to 190. Don't know, but if it doesn't stop at 160 I'll take the thermostat out and try it without it. If it heats then, it must be the exchanger.

I changed the oil filter today. I've been using Napa filters, and I bought the Mercuriser that is recommended. It's a long shot, but who know. A $10.00 fix if it helps.

Any more ideas?

 

[John_S]

Re: Oil pressure regulator

When the engine is running hot, the oil is thinner, and can cause lower oil pressure at idle. Not sure about high pressure while running, though.

 

[cprbr]

Re: Oil pressure regulator

Here's one for the book: I did all that I mentioned; flushed the heat exchanger, replaced the oil filter, checked the impeller, the whole nine yards. I even started it with the heat exchanger open, and watched the water flow through it. The exhaust risers heated to 150 degrees, so I shut it down in 30 seconds and put it back together. After it cooled, I started it and ran for about half an hour. The oil pressure stayed close to 55 pounds, hot and cold, reved and idle. The temperature went slowly up to 165 and only varied downward when I reved it up. The exhaust risers cooled to 75 degrees.

I think I'm good to go. I'll never use another NAPA oil filter on my boat. Mercrusier is all I'll put on it!!!!!

Thanks to all for your input.

Chuck