Fluctuating Oil Pressure

[Montroe]

Gentlemen,<br />I purchased a 1989 Sea Ray 160 with a GM 4-Cylinder motor and OMC Cobra outdrive. The boat was a barley running project boat and it appears that the motor and/or outdrive are not original. My problem is that the valves are very noisy and the oil pressure fluctuates from 40 psi (usually when cold) to 10 psi. The oil pressure is pretty stable at ~40 psi when the valve cover is removed. When on the water, the motor runs well up to 2500 RPM’s above that the boat does not move any faster and the motor sounds like it is going to throw a rod. The boat is also usually hard to start (engine turns slowly) when it is hot. The highest temperature that I have seen on land with a garden hose attached is 180 degrees, in the water this time of year it usually stays under 150 degrees. I have also noticed oil in the bilge but I have no idea where it is coming from. Compression is between 131 and 150 on all four cylinders. Thanks in advance for any assistance.

 

[Haut Medoc]

Re: Fluctuating Oil Pressure

Welcome to iboats What kind of oil in the bilge, & how much? Have you checked the timing at all? Since you are in PSL, you do both brackish & salt water, I assume.....My best friend lives right off of PSL Blvd, (by the turnpike), anyway.....Your compression #'s sound O.K., but I'm wondering if you had any submersion problems.....I'm not at all familiar with OMC at all, but there are many on this forum who are.....If you can post a serial # that would be very helpful......Tell us what routine maintenence has been performed....Again, welcome ......JK

 

[Don S]

Re: Fluctuating Oil Pressure

Sounds like you may have a lot of work to do on your "Project" boat before it's usable.<br />Have you done a tuneup and actually checked the point dwell,static timing and advance timing?<br />To check your oil pressure, just hook up a mechanical gauge temporarily on the engine to see what your actual pressure is.<br />Your noise is going to be another fun thing to describe. Are you sure it's the engine knocking or is it pinging.... or is it even the engine. Could it be coming from the back of the engine and actuall coming from the drive. The reason I ask is the Oil in the bilge. If the bellows has a hole in it, water will get into the ujoints, gimbal bearing and the drive itself. When water gets into the drive it pushes oil back out of the drive into the bellows and leaks through the gimbal bearing and into the drive. That same water will also get into the ujoints and gimbal bearing and cause them to make a lot of ugly sounds.<br />Best thing to do is pull the drive and inspect the ujoints.<br />If the boat has been sitting for a long time with water in it, that may very well be the reason for your low rpm, and not an engine problem.<br />You could also have air leaks or plugged screens and fittings in the fuel system causing the problem.<br />If the engine is actually running at 180° on the hose, you might also want to look at the impeller, it's probably shot. The engine shouldn't see more than about 140° on the hose.

 

[Montroe]

Re: Fluctuating Oil Pressure

Thanks for the input guys! JK, I live near PSL Blvd and Gatlin which is very close to your best friend. I take my boats out at Riverview park which is near PSL Blvd and Midport. As you stated, the St Lucie River is brackish water. Don, I found part of the problem this morning. The PO was running an electric fuel pump in series with the mechanical pump. He plugged the return line on the mechanical pump which was causing the motor to start and run against pressure. The oil level has not changed in the outdrive nor is it taking on water. I have a feeling that I really need to check the timing and give it a really good tune-up before I pull the motor and drive. Thanks again or the input.

 

[Don S]

Re: Fluctuating Oil Pressure

You probably don't need to pull the motor, pulling the drive is an annual maintenance type item to do for lubing the ujoints, gimbal bearing and checking the alignment.<br />With that fuel pump setup, sounds like he was trying to overcome a fuel starvation problem without fixing the problem.<br />Check the fuel tank pickup tube. There is a screen on it. If it gets plugged the first thing to go is the high rpms under load due to lack of fuel.