new engine oil pressure

[miles917]

1988 4.3l OMC Cobra

Another issue with this lovely boat, I had a guy install a reman. engine a couple months back and haven't had a chance to break it in yet as I've had other issues which now are resolved. Thanks.

The oil pressure is reading around 50 psi at idle and quickly jumps to 70 - 80 with throttle. Can't tell you the exact rpms as that issue comes next.

Main question: is it normal for an engine to have high oil pressure during break-in?

Unless I hear yes, tomorrow I will be checking the sending unit and gauge. If those are good I will be contacting the engine builders to see if they put in the wrong oil pump.

Other than that, what else should I be looking at.

Thanks

 

[miles917]

Re: new engine oil pressure

I know its late, hopefully more OMC diehards tomorrow.

As a general rule, what is normal oil pressure? at idle? in gear?

 

[Uraijit]

Re: new engine oil pressure

Chevy engines tend to have pretty high oil pressure. 40-50 at idle is pretty much the norm. Especially before break-in is complete. I wouldn't worry too much about it.

However, during break-in, it's VERY important to check the oil level religiously. If you don't, you might soon be sharing the same story as me: http://forums.iboats.com/showpost.php?p=1776335&postcount=17

If you don't have at least couple of quarts of oil on the boat with you, go out and buy some before you put it on the water again. Don't end up like me!

 

[miles917]

Re: new engine oil pressure

Just checked the sending unit and got opposite readings that the manual states are correct. It showed no continuity without engine running and continuity with engine running. So must be bad, any idea how to get that thing off?

 

[Uraijit]

Re: new engine oil pressure

What manual are you using?

It's not a matter of "continuity". It's a matter of resistance. The lower the oil pressure, the higher the resistance. Depending on the sending unit, resistance should be either in the 220 ohm range, or the 120 ohm range when the engine is off.

As pressure rises, the resistance will fall. Depending on pressure, it may fall as low as 10 ohms or so...

 

[miles917]

Re: new engine oil pressure

I'm still loooking for a OMC manual.....with that said....its a clymers.

With the engine off, it showed resistance. Engine running, it showed no resistance. Thats opposite of what I beleive that manual was trying to show with the continuity/no continuity.

I know clymers isnt the right manual to be using but is it just dead wrong?

Thanks Uraijit, I appreciate the help

 

[miles917]

Re: new engine oil pressure

Just went and checked again. .245 on the 2K setting with no power. These things confuse me but thats 490 ohms of resistance right? And still no resistance with the engine running.

If thats ok please let me know. I still feel 80psi oil pressure is too high at any RPM but It wouldnt be the first time I was wrong.

 

[Uraijit]

Re: new engine oil pressure

You want lower resistance with the motor running.

Disconnect the wire from the sending unit, and touch the positive lead on your multimeter to the terminal. Ground the other lead to the block. With the engine off, you should have higher resistance (either the 120, or 220 range).

Then fire the engine up, and test it again. It should be much lower.

The only real way to know if the unit is accurate, is to compare the gauges, or the resistance to the actual gauge, and see how they compare.

Of course, you'll need a manual to know exactly what resistance to look for at what pressure... But I don't think you really have a problem in the first place. The numbers you're seeing on the gauge are well within a normal range. Methinks you're making this harder than it really is.

 

[miles917]

Re: new engine oil pressure

Okie Dokie, sounds good and I'll drop it. Oil pressure and sending unit are operating normal. Guess I'll have to spend my money on some beer and hit the water. Thanks!

 

[Uraijit]

Re: new engine oil pressure

I was posting when you made your other post.

Your reading is 245 ohms, which seems about right. If you're getting zero resistance at all with the engine running, the unit is bad.

But set your multimeter to a lower setting. 2k ohms is pretty high to be getting an accurate reading.

 

[miles917]

Re: new engine oil pressure

I'm getting confused. Anywho, I checked again, same resistance 245 with engine off and now 68 ohms while running. So its good right?

It was just showing 60psi oil pressure at 1000 rpm and was hitting 80 and over with just a little revving. (2000rpm-ish) If thats ok then I'll take your word for it and go boating.

Appreciate it.

 

[miles917]

Re: new engine oil pressure

Just thought I'd say you were right about the sending unit. I wouldn't let it go so I bought a pressure tester, pulled the sending unit, hooked it up and got the exact same reading I was getting on the 20 year old gauge that they conveniently put right in front of the steering wheel.

57 at 1000rpm, 70 at 2000, and 80-85 at 3000/3500 but ofcourse I won't be hitting that high for atleast 10 hours of break-in time.

Thanks again

 

[Uraijit]

Re: new engine oil pressure

No prob. Glad you've got some peace of mind.

 

[fishrdan]

Re: new engine oil pressure

That oil pressure seems real high to me. 10-20 PSI at idle and then upwards of 50 PSI at WOT is OK, but 40 PSI at idle and 80 PSI at 3000 is too much.

What type of rebuild was this, a marine specific engine or an automotive engine. Did they install a high volume / high pressure pump? Hope not...

 

[Uraijit]

Re: new engine oil pressure

That oil pressure seems real high to me. 10-20 PSI at idle and then upwards of 50 PSI at WOT is OK, but 40 PSI at idle and 80 PSI at 3000 is too much.

What type of rebuild was this, a marine specific engine or an automotive engine. Did they install a high volume / high pressure pump? Hope not...

Okay, so maybe I'm wrong with boat engines, but I've seen TONS of Chevy engines which run at those pressures in cars--especially when it's a brand-new engine. Everything's still super tight in a new engine, so oil pressure's going to be a bit highter.

What's wrong with a high volume oil pump?

If he was having a problem of too much volume, he'd be sucking his pan dry, and that would cause ZERO pressure.

 

[miles917]

Re: new engine oil pressure

I thought about the oil pump and am waiting for a call back from the builder. If it is a high volume I think I have enough clearance to pull the oil pan without pulling the engine.....i hope.

Still getting ready to take the boat out for a hour or two. I think I should be able to get away with it as I won't be hitting WOT as its breakin time.

The thing that kills me is 100+ people have read this thread and only one jumped up and said wait, that don't sound right. Anywho will see how it goes and take is slow.

Thanks

 

[fishrdan]

Re: new engine oil pressure

Run a search about high oil pressure and you will see similar responses. A high volume/high pressure oil pump in a marine engine is not a good thing, sucking the pan dry is one of the reasons. Most recommend a high quality stock (volume & pressure) oil pump.

 

[Uraijit]

Re: new engine oil pressure

Run a search about high oil pressure and you will see similar responses. A high volume/high pressure oil pump in a marine engine is not a good thing, sucking the pan dry is one of the reasons. Most recommend a high quality stock (volume & pressure) oil pump.

Of course, this assumes that a high-volume pump is used, without a high-volume pan.

Again, if he was having a problem of sucking it dry, it would be a problem of NO oil pressure, not too much pressure...

 

[fishrdan]

Re: new engine oil pressure

He has not run it for en extended period of time at WOT yet...

 

[searay3]

Re: new engine oil pressure

Not seeing where you have in your post that the engine has been run at operating temp yet. Once the engine and oil reach temp the pressure will go down. Cold oil pressure is not accurate, especially if your running like 20w50..